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Flett S, Garcia J, Cowley KC. Spinal electrical stimulation to improve sympathetic autonomic functions needed for movement and exercise after spinal cord injury: a scoping clinical review. J Neurophysiol 2022; 128:649-670. [PMID: 35894427 DOI: 10.1152/jn.00205.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Spinal cord injury (SCI) results in sensory, motor and autonomic dysfunction. Obesity, cardiovascular and metabolic diseases are highly prevalent after SCI. Although inadequate voluntary activation of skeletal muscle contributes, it is absent or inadequate activation of thoracic spinal sympathetic neural circuitry and sub-optimal activation of homeostatic (cardiovascular, temperature) and metabolic support systems that truly limits exercise capacity, particularly for those with cervical SCI. Thus, when electrical spinal cord stimulation (SCS) studies aimed at improving motor functions began mentioning effects on exercise-related autonomic functions, a potential new area of clinical application appeared. To survey this new area of potential benefit, we performed a systematic scoping review of clinical SCS studies involving these spinally mediated autonomic functions. Nineteen studies were included, 8 used transcutaneous and 11 used epidural SCS. Improvements in BP at rest or in response to orthostatic challenge were investigated most systematically, whereas reports of improved temperature regulation, whole body metabolism and peak exercise performance were mainly anecdotal. Effective stimulation locations and parameters varied between studies, suggesting multiple stimulation parameters and rostrocaudal spinal locations may influence the same sympathetic function. Brainstem and spinal neural mechanisms providing excitatory drive to sympathetic neurons that activate homeostatic and metabolic tissues that provide support for movement and exercise and their integration with locomotor neural circuitry are discussed. A unifying conceptual framework for the integrated neural control of locomotor and sympathetic function is presented which may inform future research needed to take full advantage of SCS for improving these spinally mediated autonomic functions.
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Affiliation(s)
- Sarah Flett
- Department of Physiology and Pathophysiology, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Juanita Garcia
- Department of Physiology and Pathophysiology, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Kristine C Cowley
- Department of Physiology and Pathophysiology, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
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2
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Diversified physiological sensory input connectivity questions the existence of distinct classes of spinal interneurons. iScience 2022; 25:104083. [PMID: 35372805 PMCID: PMC8971951 DOI: 10.1016/j.isci.2022.104083] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Revised: 02/14/2022] [Accepted: 03/14/2022] [Indexed: 12/21/2022] Open
Abstract
The spinal cord is engaged in all forms of motor performance but its functions are far from understood. Because network connectivity defines function, we explored the connectivity of muscular, tendon, and tactile sensory inputs among a wide population of spinal interneurons in the lower cervical segments. Using low noise intracellular whole cell recordings in the decerebrated, non-anesthetized cat in vivo, we could define mono-, di-, and trisynaptic inputs as well as the weights of each input. Whereas each neuron had a highly specific input, and each indirect input could moreover be explained by inputs in other recorded neurons, we unexpectedly also found the input connectivity of the spinal interneuron population to form a continuum. Our data hence contrasts with the currently widespread notion of distinct classes of interneurons. We argue that this suggested diversified physiological connectivity, which likely requires a major component of circuitry learning, implies a more flexible functionality.
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McMahon C, Kowalski DP, Krupka AJ, Lemay MA. Single-cell and ensemble activity of lumbar intermediate and ventral horn interneurons in the spinal air-stepping cat. J Neurophysiol 2022; 127:99-115. [PMID: 34851739 PMCID: PMC8721903 DOI: 10.1152/jn.00202.2021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Revised: 11/30/2021] [Accepted: 12/01/2021] [Indexed: 12/18/2022] Open
Abstract
We explored the relationship between population interneuronal network activation and motor output in the adult, in vivo, air-stepping, spinal cat. By simultaneously measuring the activity of large numbers of spinal interneurons, we explored ensembles of coherently firing interneurons and their relation to motor output. In addition, the networks were analyzed in relation to their spatial distribution along the lumbar enlargement for evidence of localized groups driving particular phases of the locomotor step cycle. We simultaneously recorded hindlimb EMG activity during stepping and extracellular signals from 128 channels across two polytrodes inserted within lamina V-VII of two separate lumbar segments. Results indicated that spinal interneurons participate in one of two ensembles that are highly correlated with the flexor or the extensor muscle bursts during stepping. Interestingly, less than half of the isolated single units were significantly unimodally tuned during the step cycle whereas >97% of the single units of the ensembles were significantly correlated with muscle activity. These results show the importance of population scale analysis in neural studies of behavior as there is a much greater correlation between muscle activity and ensemble firing than between muscle activity and individual neurons. Finally, we show that there is no correlation between interneurons' rostrocaudal locations within the lumbar enlargement and their preferred phase of firing or ensemble participation. These findings indicate that spinal interneurons of lamina V-VII encoding for different phases of the locomotor cycle are spread throughout the lumbar enlargement in the adult spinal cord.NEW & NOTEWORTHY We report on the ensemble organization of interneuronal activity in the spinal cord during locomotor movements and show that lumbar intermediate zone interneurons organize in two groups related to the two major phases of walking: stance and swing. Ensemble organization is also shown to better correlate with muscular output than single-cell activity, although ensemble membership does not appear to be somatotopically organized within the spinal cord.
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Affiliation(s)
- Chantal McMahon
- School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, Pennsylvania
| | - David P Kowalski
- School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, Pennsylvania
| | | | - Michel A Lemay
- Department of Bioengineering, Temple University, Philadelphia, Pennsylvania
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4
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Abstract
When animals walk overground, mechanical stimuli activate various receptors located in muscles, joints, and skin. Afferents from these mechanoreceptors project to neuronal networks controlling locomotion in the spinal cord and brain. The dynamic interactions between the control systems at different levels of the neuraxis ensure that locomotion adjusts to its environment and meets task demands. In this article, we describe and discuss the essential contribution of somatosensory feedback to locomotion. We start with a discussion of how biomechanical properties of the body affect somatosensory feedback. We follow with the different types of mechanoreceptors and somatosensory afferents and their activity during locomotion. We then describe central projections to locomotor networks and the modulation of somatosensory feedback during locomotion and its mechanisms. We then discuss experimental approaches and animal models used to investigate the control of locomotion by somatosensory feedback before providing an overview of the different functional roles of somatosensory feedback for locomotion. Lastly, we briefly describe the role of somatosensory feedback in the recovery of locomotion after neurological injury. We highlight the fact that somatosensory feedback is an essential component of a highly integrated system for locomotor control. © 2021 American Physiological Society. Compr Physiol 11:1-71, 2021.
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Affiliation(s)
- Alain Frigon
- Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Quebec, Canada
| | - Turgay Akay
- Department of Medical Neuroscience, Atlantic Mobility Action Project, Brain Repair Center, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Boris I Prilutsky
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
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5
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Merlet AN, Harnie J, Frigon A. Inhibition and Facilitation of the Spinal Locomotor Central Pattern Generator and Reflex Circuits by Somatosensory Feedback From the Lumbar and Perineal Regions After Spinal Cord Injury. Front Neurosci 2021; 15:720542. [PMID: 34393721 PMCID: PMC8355562 DOI: 10.3389/fnins.2021.720542] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2021] [Accepted: 07/08/2021] [Indexed: 02/03/2023] Open
Abstract
Somatosensory feedback from peripheral receptors dynamically interacts with networks located in the spinal cord and brain to control mammalian locomotion. Although somatosensory feedback from the limbs plays a major role in regulating locomotor output, those from other regions, such as lumbar and perineal areas also shape locomotor activity. In mammals with a complete spinal cord injury, inputs from the lumbar region powerfully inhibit hindlimb locomotion, while those from the perineal region facilitate it. Our recent work in cats with a complete spinal cord injury shows that they also have opposite effects on cutaneous reflexes from the foot. Lumbar inputs increase the gain of reflexes while those from the perineal region decrease it. The purpose of this review is to discuss how somatosensory feedback from the lumbar and perineal regions modulate the spinal locomotor central pattern generator and reflex circuits after spinal cord injury and the possible mechanisms involved. We also discuss how spinal cord injury can lead to a loss of functional specificity through the abnormal activation of functions by somatosensory feedback, such as the concurrent activation of locomotion and micturition. Lastly, we discuss the potential functions of somatosensory feedback from the lumbar and perineal regions and their potential for promoting motor recovery after spinal cord injury.
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Affiliation(s)
- Angèle N Merlet
- Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Centre de Recherche du CHUS, Université de Sherbrooke, Sherbrooke, QC, Canada
| | - Jonathan Harnie
- Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Centre de Recherche du CHUS, Université de Sherbrooke, Sherbrooke, QC, Canada
| | - Alain Frigon
- Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Centre de Recherche du CHUS, Université de Sherbrooke, Sherbrooke, QC, Canada
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6
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Klishko AN, Akyildiz A, Mehta-Desai R, Prilutsky BI. Common and distinct muscle synergies during level and slope locomotion in the cat. J Neurophysiol 2021; 126:493-515. [PMID: 34191619 DOI: 10.1152/jn.00310.2020] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Although it is well established that the motor control system is modular, the organization of muscle synergies during locomotion and their change with ground slope are not completely understood. For example, typical reciprocal flexor-extensor muscle synergies of level walking in cats break down in downslope: one-joint hip extensors are silent throughout the stride cycle, whereas hindlimb flexors demonstrate an additional stance phase-related electromyogram (EMG) burst (Smith JL, Carlson-Kuhta P, Trank TV. J Neurophysiol 79: 1702-1716, 1998). Here, we investigated muscle synergies during level, upslope (27°), and downslope (-27°) walking in adult cats to examine common and distinct features of modular organization of locomotor EMG activity. Cluster analysis of EMG burst onset-offset times of 12 hindlimb muscles revealed five flexor and extensor burst groups that were generally shared across slopes. Stance-related bursts of flexor muscles in downslope were placed in a burst group from level and upslope walking formed by the rectus femoris. Walking upslope changed swing/stance phase durations of level walking but not the cycle duration. Five muscle synergies computed using non-negative matrix factorization accounted for at least 95% of variance in EMG patterns in each slope. Five synergies were shared between level and upslope walking, whereas only three of those were shared with downslope synergies; these synergies were active during the swing phase and phase transitions. Two stance-related synergies of downslope walking were distinct; they comprised a mixture of flexors and extensors. We suggest that the modular organization of muscle activity during level and slope walking results from interactions between motion-related sensory feedback, CPG, and supraspinal inputs.NEW & NOTEWORTHY We demonstrated that the atypical EMG activities during cat downslope walking, silent one-joint hip extensors and stance-related EMG bursts in flexors, have many features shared with activities of level and upslope walking. Majority of EMG burst groups and muscle synergies were shared among these slopes, and upslope modulated the swing/stance phase duration but not cycle duration. Thus, synergistic EMG activities in all slopes might result from a shared CPG receiving somatosensory and supraspinal inputs.
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Affiliation(s)
- Alexander N Klishko
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia
| | - Adil Akyildiz
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia
| | - Ricky Mehta-Desai
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia
| | - Boris I Prilutsky
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia
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7
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Spinal Inhibitory Interneurons: Gatekeepers of Sensorimotor Pathways. Int J Mol Sci 2021; 22:ijms22052667. [PMID: 33800863 PMCID: PMC7961554 DOI: 10.3390/ijms22052667] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Revised: 02/26/2021] [Accepted: 03/04/2021] [Indexed: 12/20/2022] Open
Abstract
The ability to sense and move within an environment are complex functions necessary for the survival of nearly all species. The spinal cord is both the initial entry site for peripheral information and the final output site for motor response, placing spinal circuits as paramount in mediating sensory responses and coordinating movement. This is partly accomplished through the activation of complex spinal microcircuits that gate afferent signals to filter extraneous stimuli from various sensory modalities and determine which signals are transmitted to higher order structures in the CNS and to spinal motor pathways. A mechanistic understanding of how inhibitory interneurons are organized and employed within the spinal cord will provide potential access points for therapeutics targeting inhibitory deficits underlying various pathologies including sensory and movement disorders. Recent studies using transgenic manipulations, neurochemical profiling, and single-cell transcriptomics have identified distinct populations of inhibitory interneurons which express an array of genetic and/or neurochemical markers that constitute functional microcircuits. In this review, we provide an overview of identified neural components that make up inhibitory microcircuits within the dorsal and ventral spinal cord and highlight the importance of inhibitory control of sensorimotor pathways at the spinal level.
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8
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Merlet AN, Harnie J, Macovei M, Doelman A, Gaudreault N, Frigon A. Cutaneous inputs from perineal region facilitate spinal locomotor activity and modulate cutaneous reflexes from the foot in spinal cats. J Neurosci Res 2021; 99:1448-1473. [PMID: 33527519 DOI: 10.1002/jnr.24791] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 11/25/2020] [Accepted: 12/23/2020] [Indexed: 12/27/2022]
Abstract
It is well known that mechanically stimulating the perineal region potently facilitates hindlimb locomotion and weight support in mammals with a spinal transection (spinal mammals). However, how perineal stimulation mediates this excitatory effect is poorly understood. We evaluated the effect of mechanically stimulating (vibration or pinch) the perineal region on ipsilateral (9-14 ms onset) and contralateral (14-18 ms onset) short-latency cutaneous reflex responses evoked by electrically stimulating the superficial peroneal or distal tibial nerve in seven adult spinal cats where hindlimb movement was restrained. Cutaneous reflexes were evoked before, during, and after mechanical stimulation of the perineal region. We found that vibration or pinch of the perineal region effectively triggered rhythmic activity, ipsilateral and contralateral to nerve stimulation. When electrically stimulating nerves, adding perineal stimulation modulated rhythmic activity by decreasing cycle and burst durations and by increasing the amplitude of flexors and extensors. Perineal stimulation also disrupted the timing of the ipsilateral rhythm, which had been entrained by nerve stimulation. Mechanically stimulating the perineal region decreased ipsilateral and contralateral short-latency reflex responses evoked by cutaneous inputs, a phenomenon we observed in muscles crossing different joints and located in different limbs. The results suggest that the excitatory effect of perineal stimulation on locomotion and weight support is mediated by increasing the excitability of central pattern-generating circuitry and not by increasing excitatory inputs from cutaneous afferents of the foot. Our results are consistent with a state-dependent modulation of reflexes by spinal interneuronal circuits.
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Affiliation(s)
- Angèle N Merlet
- Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, QC, Canada
| | - Jonathan Harnie
- Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, QC, Canada
| | - Madalina Macovei
- Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, QC, Canada
| | - Adam Doelman
- Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, QC, Canada
| | - Nathaly Gaudreault
- School of Rehabilitation, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, QC, Canada.,Centre de Recherche du CHUS, Sherbrooke, QC, Canada
| | - Alain Frigon
- Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, QC, Canada.,Centre de Recherche du CHUS, Sherbrooke, QC, Canada
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9
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Domínguez-Rodríguez LE, Stecina K, García-Ramírez DL, Mena-Avila E, Milla-Cruz JJ, Martínez-Silva L, Zhang M, Hultborn H, Quevedo JN. Candidate Interneurons Mediating the Resetting of the Locomotor Rhythm by Extensor Group I Afferents in the Cat. Neuroscience 2020; 450:96-112. [PMID: 32946952 DOI: 10.1016/j.neuroscience.2020.09.017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 08/07/2020] [Accepted: 09/04/2020] [Indexed: 10/23/2022]
Abstract
Sensory information arising from limb movements controls the spinal locomotor circuitry to adapt the motor pattern to demands of the environment. Stimulation of extensor group (gr) I afferents during fictive locomotion in decerebrate cats prolongs the ongoing extension, and terminates ongoing flexion with an initiation of the subsequent extension, i. e. "resetting to extension". Moreover, instead of the classical Ib non-reciprocal inhibition, stimulation of extensor gr I afferents produces a polysynaptic excitation in extensor motoneurons with latencies (∼3.5-4.0 ms) compatible with 3 interposed interneurons. We assume that some interneurons in this pathway actually belong to the rhythm-generating layer of the locomotor Central Pattern Generator (CPG), since their activity was correlated to a resetting of the rhythm. In the present work fictive locomotion was (mostly) induced by i.v. injection of nialamide followed by l-DOPA in paralyzed cats following decerebration and spinalization at C1 level. In some experiments, we extended previous observations during fictive locomotion on the emergence and locomotor state-dependence of polysynaptic excitatory postsynaptic potentials from extensor gr I afferents to ankle extensor motoneurons. However, the main focus was to record location and properties of interneurons (n = 62) that (i) were active during the extensor phase of fictive locomotion and (ii) received short-latency excitation (mono-, di- or polysynaptic) from extensor gr I afferents. We conclude that the interneurons recorded fulfill the characteristics to belong to the neuronal pathway activated by extensor gr I afferents during locomotion, and may contribute to the 'resetting to extension' as part of the locomotor CPG.
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Affiliation(s)
| | - K Stecina
- Spinal Cord Research Centre, University of Manitoba, Winnipeg, Canada; Dept. of Neuroscience, University of Copenhagen, Denmark
| | - D L García-Ramírez
- Dept. of Physiology, Biophysics and Neuroscience, CINVESTAV del IPN, Mexico City, Mexico; Department of Neurobiology & Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
| | - E Mena-Avila
- Dept. of Physiology, Biophysics and Neuroscience, CINVESTAV del IPN, Mexico City, Mexico
| | - J J Milla-Cruz
- Dept. of Physiology, Biophysics and Neuroscience, CINVESTAV del IPN, Mexico City, Mexico
| | - L Martínez-Silva
- Dept. of Physiology, Biophysics and Neuroscience, CINVESTAV del IPN, Mexico City, Mexico; Department of Pathology and Cell Biology, Columbia University, New York, NY, USA
| | - M Zhang
- Dept. of Neuroscience, University of Copenhagen, Denmark; Inst. of Molecular Medicine, Medical Faculty, University of Southern Denmark, Odense, Denmark
| | - H Hultborn
- Dept. of Neuroscience, University of Copenhagen, Denmark.
| | - J N Quevedo
- Dept. of Physiology, Biophysics and Neuroscience, CINVESTAV del IPN, Mexico City, Mexico.
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10
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Higgin D, Krupka A, Maghsoudi OH, Klishko AN, Nichols TR, Lyle MA, Prilutsky BI, Lemay MA. Adaptation to slope in locomotor-trained spinal cats with intact and self-reinnervated lateral gastrocnemius and soleus muscles. J Neurophysiol 2020; 123:70-89. [PMID: 31693435 PMCID: PMC6985865 DOI: 10.1152/jn.00018.2019] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Revised: 11/06/2019] [Accepted: 11/06/2019] [Indexed: 11/22/2022] Open
Abstract
Sensorimotor training providing motion-dependent somatosensory feedback to spinal locomotor networks restores treadmill weight-bearing stepping on flat surfaces in spinal cats. In this study, we examined if locomotor ability on flat surfaces transfers to sloped surfaces and the contribution of length-dependent sensory feedback from lateral gastrocnemius (LG) and soleus (Sol) to locomotor recovery after spinal transection and locomotor training. We compared kinematics and muscle activity at different slopes (±10° and ±25°) in spinalized cats (n = 8) trained to walk on a flat treadmill. Half of those animals had their right hindlimb LG/Sol nerve cut and reattached before spinal transection and locomotor training, a procedure called muscle self-reinnervation that leads to elimination of autogenic monosynaptic length feedback in spinally intact animals. All spinal animals trained on a flat surface were able to walk on slopes with minimal differences in walking kinematics and muscle activity between animals with/without LG/Sol self-reinnervation. We found minimal changes in kinematics and muscle activity at lower slopes (±10°), indicating that walking patterns obtained on flat surfaces are robust enough to accommodate low slopes. Contrary to results in spinal intact animals, force responses to muscle stretch largely returned in both SELF-REINNERVATED muscles for the trained spinalized animals. Overall, our results indicate that the locomotor patterns acquired with training on a level surface transfer to walking on low slopes and that spinalization may allow the recovery of autogenic monosynaptic length feedback following muscle self-reinnervation.NEW & NOTEWORTHY Spinal locomotor networks locomotor trained on a flat surface can adapt the locomotor output to slope walking, up to ±25° of slope, even with total absence of supraspinal CONTROL. Autogenic length feedback (stretch reflex) shows signs of recovery in spinalized animals, contrary to results in spinally intact animals.
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Affiliation(s)
- Dwight Higgin
- Department of Biological Sciences, University of Delaware, Wilmington, Delaware
| | - Alexander Krupka
- Department of Natural Science, DeSales University, Center Valley, Pennsylvania
| | | | - Alexander N Klishko
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia
| | - T Richard Nichols
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia
| | - Mark A Lyle
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia
| | - Boris I Prilutsky
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia
| | - Michel A Lemay
- Department of Bioengineering, Temple University, Philadelphia, Pennsylvania
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11
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Contento VS, Dalton BH, Power GA. The Inhibitory Tendon-Evoked Reflex Is Increased in the Torque-Enhanced State Following Active Lengthening Compared to a Purely Isometric Contraction. Brain Sci 2019; 10:brainsci10010013. [PMID: 31878094 PMCID: PMC7016668 DOI: 10.3390/brainsci10010013] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Revised: 12/16/2019] [Accepted: 12/18/2019] [Indexed: 11/16/2022] Open
Abstract
Residual torque enhancement (rTE) is a history-dependent property of muscle, which results in an increase in steady-state isometric torque production following an active lengthening contraction as compared to a purely isometric (ISO) contraction at the same muscle length and level of activation. Once thought to be only an intrinsic property of muscle, recent evidence during voluntary contractions indicates a neuromechanical coupling between motor neuron excitability and the contractile state of the muscle. However, the mechanism by which this occurs has yet to be elucidated. The purpose of this study was to investigate inhibition arising from tendon-mediated feedback (e.g., Golgi tendon organ; GTO) through tendon electrical stimulation (TStim) in the ISO and rTE states during activation-matching and torque-matching tasks. Fourteen male participants (22 ± 2 years) performed 10 activation-matching contractions at 40% of their maximum tibialis anterior electromyography amplitude (5 ISO/5 rTE) and 10 torque-matching contractions at 40% of their maximum dorsiflexion torque (5 ISO/5 rTE). During both tasks, 10 TStim were delivered during the isometric steady state of all contractions, and the resulting tendon-evoked inhibitory reflexes were averaged and analyzed. Reflex amplitude increased by ~23% in the rTE state compared to the ISO state for the activation-matching task, and no differences were detected for the torque-matching task. The current data indicate an important relationship between afferent feedback in the torque-enhanced state and voluntary control of submaximal contractions. The history-dependent properties of muscle is likely to alter motor neuron excitability through modifications in tension- or torque-mediated afferent feedback arising from the tendon.
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Affiliation(s)
- Vincenzo S. Contento
- Department of Human Health and Nutritional Sciences, College of Biological Sciences, University of Guelph, Guelph, ON N1G 2W1, Canada;
| | - Brian H. Dalton
- School of Health and Exercise Science, University of British Columbia, Kelowna, BC V1V 1V7, Canada;
| | - Geoffrey A. Power
- Department of Human Health and Nutritional Sciences, College of Biological Sciences, University of Guelph, Guelph, ON N1G 2W1, Canada;
- Correspondence:
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12
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Grillner S, El Manira A. Current Principles of Motor Control, with Special Reference to Vertebrate Locomotion. Physiol Rev 2019; 100:271-320. [PMID: 31512990 DOI: 10.1152/physrev.00015.2019] [Citation(s) in RCA: 216] [Impact Index Per Article: 43.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The vertebrate control of locomotion involves all levels of the nervous system from cortex to the spinal cord. Here, we aim to cover all main aspects of this complex behavior, from the operation of the microcircuits in the spinal cord to the systems and behavioral levels and extend from mammalian locomotion to the basic undulatory movements of lamprey and fish. The cellular basis of propulsion represents the core of the control system, and it involves the spinal central pattern generator networks (CPGs) controlling the timing of different muscles, the sensory compensation for perturbations, and the brain stem command systems controlling the level of activity of the CPGs and the speed of locomotion. The forebrain and in particular the basal ganglia are involved in determining which motor programs should be recruited at a given point of time and can both initiate and stop locomotor activity. The propulsive control system needs to be integrated with the postural control system to maintain body orientation. Moreover, the locomotor movements need to be steered so that the subject approaches the goal of the locomotor episode, or avoids colliding with elements in the environment or simply escapes at high speed. These different aspects will all be covered in the review.
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Affiliation(s)
- Sten Grillner
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
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13
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Horstman GM, Housley SN, Cope TC. Dysregulation of mechanosensory circuits coordinating the actions of antagonist motor pools following peripheral nerve injury and muscle reinnervation. Exp Neurol 2019; 318:124-134. [PMID: 31039333 PMCID: PMC6588415 DOI: 10.1016/j.expneurol.2019.04.017] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2019] [Revised: 03/23/2019] [Accepted: 04/26/2019] [Indexed: 12/29/2022]
Abstract
Movement disorders observed following peripheral nerve injury and muscle reinnervation suggest discoordination in the activation of antagonist muscles. Although underlying mechanisms remain undecided, dysfunction in spinal reflex circuits is a reasonable candidate. Based on the well known role of reflex inhibition between agonist and antagonist muscles in normal animals, we hypothesized its reduction following muscle reinnervation, similar to that associated with other disorders exhibiting antagonist discoordination, e.g. spinal cord injury and dystonia. Experiments performed on acutely-decerebrated rats examined interactions of mechanosensory reflexes between ipsilateral muscles acting as mechanical antagonists at the ankle joint: ankle extensor, gastrocnemii (G) muscles (agonists) and ankle flexor, tibialis anterior (TA) muscle (antagonist). The force of agonist stretch reflex contraction was measured for its suppression or facilitation by concurrent conditioning stretch of the antagonist muscle. Data were compared between two groups of adult rats, an antagonist reinnervation group with TA muscle reinnervated and a control group with TA normally innervated. Results revealed a three-fold increase in reflex suppression in the antagonist reinnervation group, contrary to our predicted decrease. Reflex facilitation also increased, not only in strength, seven-fold, but also in its frequency of stochastic occurrence across stimulus trials. These observations suggest dysregulation in specific spinal reflex circuits as novel candidate origins of modified antagonist muscle coordination following peripheral nerve injury and muscle reinnervation.
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Affiliation(s)
- Gabrielle M Horstman
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH 45435, United States of America
| | - Stephen N Housley
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA 30332, United States of America
| | - Timothy C Cope
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH 45435, United States of America; School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA 30332, United States of America; W.H. Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Georgia Institute of Technology, Atlanta, GA 30332, United States of America.
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14
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Lockyer EJ, Benson RJ, Hynes AP, Alcock LR, Spence AJ, Button DC, Power KE. Intensity matters: effects of cadence and power output on corticospinal excitability during arm cycling are phase and muscle dependent. J Neurophysiol 2018; 120:2908-2921. [PMID: 30354778 DOI: 10.1152/jn.00358.2018] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The present study investigated the effects of cadence and power output on corticospinal excitability to the biceps (BB) and triceps brachii (TB) during arm cycling. Supraspinal and spinal excitability were assessed using transcranial magnetic stimulation (TMS) of the motor cortex and transmastoid electrical stimulation (TMES) of the corticospinal tract, respectively. Motor-evoked potentials (MEPs) elicited by TMS and cervicomedullary motor-evoked potentials (CMEPs) elicited by TMES were recorded at two positions during arm cycling corresponding to mid-elbow flexion and mid-elbow extension (i.e., 6 and 12 o'clock made relative to a clock face, respectively). Arm cycling was performed at combinations of two cadences (60 and 90 rpm) at three relative power outputs (20, 40, and 60% peak power output). At the 6 o'clock position, BB MEPs increased ~11.5% as cadence increased and up to ~57.2% as power output increased ( P < 0.05). In the TB, MEPs increased ~15.2% with cadence ( P = 0.013) but were not affected by power output, while CMEPs increased with cadence (~16.3%) and power output (up to ~19.1%, P < 0.05). At the 12 o'clock position, BB MEPs increased ~26.8% as cadence increased and up to ~96.1% as power output increased ( P < 0.05), while CMEPs decreased ~29.7% with cadence ( P = 0.013) and did not change with power output ( P = 0.851). In contrast, TB MEPs were not different with cadence or power output, while CMEPs increased ~12.8% with cadence and up to ~23.1% with power output ( P < 0.05). These data suggest that the "type" of intensity differentially modulates supraspinal and spinal excitability in a manner that is phase- and muscle dependent. NEW & NOTEWORTHY There is currently little information available on how changes in locomotor intensity influence excitability within the corticospinal pathway. This study investigated the effects of arm cycling intensity (i.e., alterations in cadence and power output) on corticospinal excitability projecting to the biceps and triceps brachii during arm cycling. We demonstrate that corticospinal excitability is modulated differentially by cadence and power output and that these modulations are dependent on the phase and the muscle examined.
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Affiliation(s)
- E J Lockyer
- Human Neurophysiology Laboratory, School of Human Kinetics and Recreation, Memorial University of Newfoundland , St. John's, Newfoundland , Canada.,Faculty of Medicine, Memorial University of Newfoundland , St. John's, Newfoundland , Canada
| | - R J Benson
- Human Neurophysiology Laboratory, School of Human Kinetics and Recreation, Memorial University of Newfoundland , St. John's, Newfoundland , Canada
| | - A P Hynes
- Human Neurophysiology Laboratory, School of Human Kinetics and Recreation, Memorial University of Newfoundland , St. John's, Newfoundland , Canada
| | - L R Alcock
- Human Neurophysiology Laboratory, School of Human Kinetics and Recreation, Memorial University of Newfoundland , St. John's, Newfoundland , Canada
| | - A J Spence
- Human Neurophysiology Laboratory, School of Human Kinetics and Recreation, Memorial University of Newfoundland , St. John's, Newfoundland , Canada
| | - D C Button
- Human Neurophysiology Laboratory, School of Human Kinetics and Recreation, Memorial University of Newfoundland , St. John's, Newfoundland , Canada.,Faculty of Medicine, Memorial University of Newfoundland , St. John's, Newfoundland , Canada
| | - K E Power
- Human Neurophysiology Laboratory, School of Human Kinetics and Recreation, Memorial University of Newfoundland , St. John's, Newfoundland , Canada.,Faculty of Medicine, Memorial University of Newfoundland , St. John's, Newfoundland , Canada
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15
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Duysens J, Forner-Cordero A. Walking with perturbations: a guide for biped humans and robots. BIOINSPIRATION & BIOMIMETICS 2018; 13:061001. [PMID: 30109860 DOI: 10.1088/1748-3190/aada54] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
This paper provides an update on the neural control of bipedal walking in relation to bioinspired models and robots. It is argued that most current models or robots are based on the construct of a symmetrical central pattern generator (CPG). However, new evidence suggests that CPG functioning is basically asymmetrical with its flexor half linked more tightly to the rhythm generator. The stability of bipedal gait, which is an important problem for robots and biological systems, is also addressed. While it is not possible to determine how biological biped systems guarantee stability, robot solutions can be useful to propose new hypotheses for biology. In the second part of this review, the focus is on gait perturbations, which is an important topic in robotics in view of the frequent falls of robots when faced with perturbations. From the human physiology it is known that the initial reaction often consists of a brief interruption followed by an adequate response. For instance, the successful recovery from a trip is achieved using some basic reactions (termed elevating and lowering strategies), that depend on the phase of the step cycle of the trip occurrence. Reactions to stepping unexpectedly in a hole depend on comparing expected and real feedback. Implementation of these ideas in models and robotics starts to emerge, with the most advanced robots being able to learn how to fall safely and how to deal with complicated disturbances such as provided by walking on a split-belt.
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Affiliation(s)
- Jacques Duysens
- Biomechatronics Lab., Mechatronics Department, Escola Politécnica da Universidade de São Paulo, Av. Prof. Mello Moraes, 2231, Cidade Universitária 05508-030, São Paulo-SP, Brasil. Department of Kinesiology, FaBeR, Katholieke Universiteit Leuven, Leuven, Belgium
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16
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Mayer WP, Murray AJ, Brenner-Morton S, Jessell TM, Tourtellotte WG, Akay T. Role of muscle spindle feedback in regulating muscle activity strength during walking at different speed in mice. J Neurophysiol 2018; 120:2484-2497. [PMID: 30133381 DOI: 10.1152/jn.00250.2018] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Terrestrial animals increase their walking speed by increasing the activity of the extensor muscles. However, the mechanism underlying how this speed-dependent amplitude modulation is achieved remains obscure. Previous studies have shown that group Ib afferent feedback from Golgi tendon organs that signal force is one of the major regulators of the strength of muscle activity during walking in cats and humans. In contrast, the contribution of group Ia/II afferent feedback from muscle spindle stretch receptors that signal angular displacement of leg joints is unclear. Some studies indicate that group II afferent feedback may be important for amplitude regulation in humans, but the role of muscle spindle feedback in regulation of muscle activity strength in quadrupedal animals is very poorly understood. To examine the role of feedback from muscle spindles, we combined in vivo electrophysiology and motion analysis with mouse genetics and gene delivery with adeno-associated virus. We provide evidence that proprioceptive sensory feedback from muscle spindles is important for the regulation of the muscle activity strength and speed-dependent amplitude modulation. Furthermore, our data suggest that feedback from the muscle spindles of the ankle extensor muscles, the triceps surae, is the main source for this mechanism. In contrast, muscle spindle feedback from the knee extensor muscles, the quadriceps femoris, has no influence on speed-dependent amplitude modulation. We provide evidence that proprioceptive feedback from ankle extensor muscles is critical for regulating muscle activity strength as gait speed increases. NEW & NOTEWORTHY Animals upregulate the activity of extensor muscles to increase their walking speed, but the mechanism behind this is not known. We show that this speed-dependent amplitude modulation requires proprioceptive sensory feedback from muscle spindles of ankle extensor muscle. In the absence of muscle spindle feedback, animals cannot walk at higher speeds as they can when muscle spindle feedback is present.
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Affiliation(s)
- William P Mayer
- Atlantic Mobility Action Project, Brain Repair Center, Department of Medical Neuroscience, Dalhousie University , Halifax, Nova Scotia , Canada.,Department of Morphology, Federal University of Espirito Santo , Vitoria , Brazil
| | - Andrew J Murray
- Sainsbury Wellcome Center for Neural Circuits and Behaviour, University College London , London , United Kingdom
| | - Susan Brenner-Morton
- Howard Hughes Medical Institute, Department of Neuroscience, Columbia University , New York, New York
| | - Thomas M Jessell
- Howard Hughes Medical Institute, Department of Neuroscience, Columbia University , New York, New York
| | - Warren G Tourtellotte
- Department of Pathology and Laboratory Medicine, Cedar Sinai Medical Center, West Hollywood, California
| | - Turgay Akay
- Atlantic Mobility Action Project, Brain Repair Center, Department of Medical Neuroscience, Dalhousie University , Halifax, Nova Scotia , Canada
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17
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Sypkes CT, Kozlowski BJ, Grant J, Bent LR, McNeil CJ, Power GA. The influence of residual force enhancement on spinal and supraspinal excitability. PeerJ 2018; 6:e5421. [PMID: 30083481 PMCID: PMC6078065 DOI: 10.7717/peerj.5421] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2018] [Accepted: 07/21/2018] [Indexed: 11/20/2022] Open
Abstract
Background Following active muscle lengthening, there is an increase in steady-state isometric force as compared with a purely isometric contraction at the same muscle length and level of activation. This fundamental property of skeletal muscle is known as residual force enhancement (RFE). While the basic mechanisms contributing to this increase in steady-state isometric force have been well documented, changes in central nervous system (CNS) excitability for submaximal contractions during RFE are unclear. The purpose of this study was to investigate spinal and supraspinal excitability in the RFE isometric steady-state following active lengthening of the ankle dorsiflexor muscles. Methods A total of 11 male participants (20–28 years) performed dorsiflexions at a constant level of electromyographic activity (40% of maximum). Half of the contractions were purely isometric (8 s at an ankle angle of 130°), and the other half were during the RFE isometric steady-state following active lengthening (2 s isometric at 90°, a 1 s lengthening phase at 40°/s, and 5 s at 130°). Motor evoked potentials (MEPs), cervicomedullary motor evoked potentials (CMEPs), and compound muscle action potentials (M-waves) were recorded from the tibialis anterior during the purely isometric contraction and RFE isometric steady-state. Results Compared to the purely isometric condition, following active lengthening, there was 10% RFE (p < 0.05), with a 17% decrease in normalized CMEP amplitude (CMEP/Mmax) (p < 0.05) and no change in normalized MEP amplitude (MEP/CMEP) (p > 0.05). Discussion These results indicate that spinal excitability is reduced during submaximal voluntary contractions in the RFE state with no change in supraspinal excitability. These findings may have further implications to everyday life offering insight into how the CNS optimizes control of skeletal muscle following submaximal active muscle lengthening.
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Affiliation(s)
- Caleb T Sypkes
- Department of Human Health and Nutritional Sciences, College of Biological Sciences, University of Guelph, Guelph, ON, Canada
| | - Benjamin J Kozlowski
- Department of Human Health and Nutritional Sciences, College of Biological Sciences, University of Guelph, Guelph, ON, Canada
| | - Jordan Grant
- Department of Human Health and Nutritional Sciences, College of Biological Sciences, University of Guelph, Guelph, ON, Canada
| | - Leah R Bent
- Department of Human Health and Nutritional Sciences, College of Biological Sciences, University of Guelph, Guelph, ON, Canada
| | - Chris J McNeil
- School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada
| | - Geoffrey A Power
- Department of Human Health and Nutritional Sciences, College of Biological Sciences, University of Guelph, Guelph, ON, Canada
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18
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Harkema SJ, Rejc E, Angeli CA. Neuromodulation of the Spinal Cord for Movement Restoration. Neuromodulation 2018. [DOI: 10.1016/b978-0-12-805353-9.00098-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Côté MP, Murray M, Lemay MA. Rehabilitation Strategies after Spinal Cord Injury: Inquiry into the Mechanisms of Success and Failure. J Neurotrauma 2016; 34:1841-1857. [PMID: 27762657 DOI: 10.1089/neu.2016.4577] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
Abstract
Body-weight supported locomotor training (BWST) promotes recovery of load-bearing stepping in lower mammals, but its efficacy in individuals with a spinal cord injury (SCI) is limited and highly dependent on injury severity. While animal models with complete spinal transections recover stepping with step-training, motor complete SCI individuals do not, despite similarly intensive training. In this review, we examine the significant differences between humans and animal models that may explain this discrepancy in the results obtained with BWST. We also summarize the known effects of SCI and locomotor training on the muscular, motoneuronal, interneuronal, and supraspinal systems in human and non-human models of SCI and address the potential causes for failure to translate to the clinic. The evidence points to a deficiency in neuronal activation as the mechanism of failure, rather than muscular insufficiency. While motoneuronal and interneuronal systems cannot be directly probed in humans, the changes brought upon by step-training in SCI animal models suggest a beneficial re-organization of the systems' responsiveness to descending and afferent feedback that support locomotor recovery. The literature on partial lesions in humans and animal models clearly demonstrate a greater dependency on supraspinal input to the lumbar cord in humans than in non-human mammals for locomotion. Recent results with epidural stimulation that activates the lumbar interneuronal networks and/or increases the overall excitability of the locomotor centers suggest that these centers are much more dependent on the supraspinal tonic drive in humans. Sensory feedback shapes the locomotor output in animal models but does not appear to be sufficient to drive it in humans.
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Affiliation(s)
- Marie-Pascale Côté
- 1 Department of Neurobiology and Anatomy, Drexel University College of Medicine , Philadelphia, Pennsylvania
| | - Marion Murray
- 1 Department of Neurobiology and Anatomy, Drexel University College of Medicine , Philadelphia, Pennsylvania
| | - Michel A Lemay
- 2 Department of Bioengineering, Temple University , Philadelphia, Pennsylvania
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20
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Smith AC, Knikou M. A Review on Locomotor Training after Spinal Cord Injury: Reorganization of Spinal Neuronal Circuits and Recovery of Motor Function. Neural Plast 2016; 2016:1216258. [PMID: 27293901 PMCID: PMC4879237 DOI: 10.1155/2016/1216258] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Accepted: 04/20/2016] [Indexed: 01/01/2023] Open
Abstract
Locomotor training is a classic rehabilitation approach utilized with the aim of improving sensorimotor function and walking ability in people with spinal cord injury (SCI). Recent studies have provided strong evidence that locomotor training of persons with clinically complete, motor complete, or motor incomplete SCI induces functional reorganization of spinal neuronal networks at multisegmental levels at rest and during assisted stepping. This neuronal reorganization coincides with improvements in motor function and decreased muscle cocontractions. In this review, we will discuss the manner in which spinal neuronal circuits are impaired and the evidence surrounding plasticity of neuronal activity after locomotor training in people with SCI. We conclude that we need to better understand the physiological changes underlying locomotor training, use physiological signals to probe recovery over the course of training, and utilize established and contemporary interventions simultaneously in larger scale research studies. Furthermore, the focus of our research questions needs to change from feasibility and efficacy to the following: what are the physiological mechanisms that make it work and for whom? The aforementioned will enable the scientific and clinical community to develop more effective rehabilitation protocols maximizing sensorimotor function recovery in people with SCI.
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Affiliation(s)
- Andrew C. Smith
- Interdepartmental Neuroscience Program, Northwestern University, Chicago, IL 60611, USA
| | - Maria Knikou
- The Graduate Center, City University of New York, New York, NY 10016, USA
- Department of Physical Therapy, College of Staten Island, City University of New York, Staten Island, NY 10314, USA
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21
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Abstract
Human studies in the past three decades have provided us with an emerging understanding of how cortical and spinal networks collaborate to ensure the vast repertoire of human behaviors. Humans have direct cortical connections to spinal motoneurons, which bypass spinal interneurons and exert a direct (willful) muscle control with the aid of a context-dependent integration of somatosensory and visual information at cortical level. However, spinal networks also play an important role. Sensory feedback through spinal circuitries is integrated with central motor commands and contributes importantly to the muscle activity underlying voluntary movements. Regulation of spinal interneurons is used to switch between motor states such as locomotion (reciprocal innervation) and stance (coactivation pattern). Cortical regulation of presynaptic inhibition of sensory afferents may focus the central motor command by opening or closing sensory feedback pathways. In the future, human studies of spinal motor control, in close collaboration with animal studies on the molecular biology of the spinal cord, will continue to document the neural basis for human behavior.
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Affiliation(s)
- Jens Bo Nielsen
- Department of Neuroscience and Pharmacology and Department of Nutrition, Exercise and Sports, University of Copenhagen, DK-2200 Copenhagen N, Denmark;
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22
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A Neuromechanical Model of Spinal Control of Locomotion. NEUROMECHANICAL MODELING OF POSTURE AND LOCOMOTION 2016. [DOI: 10.1007/978-1-4939-3267-2_2] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Buschmann T, Ewald A, von Twickel A, Büschges A. Controlling legs for locomotion-insights from robotics and neurobiology. BIOINSPIRATION & BIOMIMETICS 2015; 10:041001. [PMID: 26119450 DOI: 10.1088/1748-3190/10/4/041001] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Walking is the most common terrestrial form of locomotion in animals. Its great versatility and flexibility has led to many attempts at building walking machines with similar capabilities. The control of walking is an active research area both in neurobiology and robotics, with a large and growing body of work. This paper gives an overview of the current knowledge on the control of legged locomotion in animals and machines and attempts to give walking control researchers from biology and robotics an overview of the current knowledge in both fields. We try to summarize the knowledge on the neurobiological basis of walking control in animals, emphasizing common principles seen in different species. In a section on walking robots, we review common approaches to walking controller design with a slight emphasis on biped walking control. We show where parallels between robotic and neurobiological walking controllers exist and how robotics and biology may benefit from each other. Finally, we discuss where research in the two fields diverges and suggest ways to bridge these gaps.
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Affiliation(s)
- Thomas Buschmann
- Technische Universität München, Institute of Applied Mechanics, Boltzmannstrasse 15, D-85747 Garching, Germany
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24
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Bui TV, Brownstone RM. Sensory-evoked perturbations of locomotor activity by sparse sensory input: a computational study. J Neurophysiol 2015; 113:2824-39. [PMID: 25673740 DOI: 10.1152/jn.00866.2014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Accepted: 02/06/2015] [Indexed: 11/22/2022] Open
Abstract
Sensory inputs from muscle, cutaneous, and joint afferents project to the spinal cord, where they are able to affect ongoing locomotor activity. Activation of sensory input can initiate or prolong bouts of locomotor activity depending on the identity of the sensory afferent activated and the timing of the activation within the locomotor cycle. However, the mechanisms by which afferent activity modifies locomotor rhythm and the distribution of sensory afferents to the spinal locomotor networks have not been determined. Considering the many sources of sensory inputs to the spinal cord, determining this distribution would provide insights into how sensory inputs are integrated to adjust ongoing locomotor activity. We asked whether a sparsely distributed set of sensory inputs could modify ongoing locomotor activity. To address this question, several computational models of locomotor central pattern generators (CPGs) that were mechanistically diverse and generated locomotor-like rhythmic activity were developed. We show that sensory inputs restricted to a small subset of the network neurons can perturb locomotor activity in the same manner as seen experimentally. Furthermore, we show that an architecture with sparse sensory input improves the capacity to gate sensory information by selectively modulating sensory channels. These data demonstrate that sensory input to rhythm-generating networks need not be extensively distributed.
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Affiliation(s)
- Tuan V Bui
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada; Centre for Neural Dynamics, University of Ottawa, Ottawa, Ontario, Canada;
| | - Robert M Brownstone
- Department of Surgery (Neurosurgery), Dalhousie University, Halifax, Nova Scotia, Canada; and Department of Medical Neuroscience, Dalhousie University, Halifax, Nova Scotia, Canada
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25
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Knikou M, Smith AC, Mummidisetty CK. Locomotor training improves reciprocal and nonreciprocal inhibitory control of soleus motoneurons in human spinal cord injury. J Neurophysiol 2015; 113:2447-60. [PMID: 25609110 DOI: 10.1152/jn.00872.2014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Accepted: 01/20/2015] [Indexed: 12/19/2022] Open
Abstract
Pathologic reorganization of spinal networks and activity-dependent plasticity are common neuronal adaptations after spinal cord injury (SCI) in humans. In this work, we examined changes of reciprocal Ia and nonreciprocal Ib inhibition after locomotor training in 16 people with chronic SCI. The soleus H-reflex depression following common peroneal nerve (CPN) and medial gastrocnemius (MG) nerve stimulation at short conditioning-test (C-T) intervals was assessed before and after training in the seated position and during stepping. The conditioned H reflexes were normalized to the unconditioned H reflex recorded during seated. During stepping, both H reflexes were normalized to the maximal M wave evoked at each bin of the step cycle. In the seated position, locomotor training replaced reciprocal facilitation with reciprocal inhibition in all subjects, and Ib facilitation was replaced by Ib inhibition in 13 out of 14 subjects. During stepping, reciprocal inhibition was decreased at early stance and increased at midswing in American Spinal Injury Association Impairment Scale C (AIS C) and was decreased at midstance and midswing phases in AIS D after training. Ib inhibition was decreased at early swing and increased at late swing in AIS C and was decreased at early stance phase in AIS D after training. The results of this study support that locomotor training alters postsynaptic actions of Ia and Ib inhibitory interneurons on soleus motoneurons at rest and during stepping and that such changes occur in cases with limited or absent supraspinal inputs.
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Affiliation(s)
- Maria Knikou
- Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois; Department of Physical Medicine and Rehabilitation, Northwestern University Feinberg Medical School, Chicago, Illinois; Graduate Center/The City University of New York, New York, New York; and Department of Physical Therapy, College of Staten Island, Staten Island, New York
| | - Andrew C Smith
- Northwestern University Interdepartmental Neuroscience Program, Chicago, Illinois
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26
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Tresch UA, Perreault EJ, Honeycutt CF. Startle evoked movement is delayed in older adults: implications for brainstem processing in the elderly. Physiol Rep 2014; 2:2/6/e12025. [PMID: 24907294 PMCID: PMC4208637 DOI: 10.14814/phy2.12025] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Little attention has been given to how age affects the neural processing of movement within the brainstem. Since the brainstem plays a critical role in motor control throughout the whole body, having a clear understanding of deficits in brainstem function could provide important insights into movement deficits in older adults. A unique property of the startle reflex is its ability to involuntarily elicit planned movements, a phenomenon referred to as startReact. The noninvasive startReact response has previously been used to probe both brainstem utilization and motor planning. Our objective was to evaluate deficits in startReact hand extension movements in older adults. We hypothesized that startReact hand extension will be intact but delayed. Electromyography was recorded from the sternocleidomastoid (SCM) muscle to detect startle and the extensor digitorum communis (EDC) to quantify movement onset in both young (24 ± 1) and older adults (70 ± 11). Subjects were exposed to a startling loud sound when prepared to extend their hand. Trials were split into those where a startle did (SCM+) and did not (SCM−) occur. We found that startReact was intact but delayed in older adults. SCM+ onset latencies were faster than SCM− trials in both the populations, however, SCM+ onset latencies were slower in older adults compared to young (Δ = 8 msec). We conclude that the observed age‐related delay in the startReact response most likely arises from central processing delays within the brainstem. Our objective was to utilize the noninvasive startReact phenomenon, which is mediated through the brainstem, to gain insight into brainstem processing in older adults. We found that startReact hand extension was intact but delayed in older adults. The observed age‐related delay in the startReact response most likely arises from central processing delays within the brainstem. Our result that the startReact response is delayed in older individuals highlights that movements (e.g., posture, locomotion) and reflexes (e.g., long‐latency stretch reflexes) that are coordinated by the brainstem may have similar deficits in older adults.
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Affiliation(s)
| | - Eric J Perreault
- Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois Department of Biomedical Engineering, Northwestern University, Evanston, Illinois Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, Illinois
| | - Claire F Honeycutt
- Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois
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Abstract
Epidural electrical stimulation (EES) of lumbosacral segments can restore a range of movements after spinal cord injury. However, the mechanisms and neural structures through which EES facilitates movement execution remain unclear. Here, we designed a computational model and performed in vivo experiments to investigate the type of fibers, neurons, and circuits recruited in response to EES. We first developed a realistic finite element computer model of rat lumbosacral segments to identify the currents generated by EES. To evaluate the impact of these currents on sensorimotor circuits, we coupled this model with an anatomically realistic axon-cable model of motoneurons, interneurons, and myelinated afferent fibers for antagonistic ankle muscles. Comparisons between computer simulations and experiments revealed the ability of the model to predict EES-evoked motor responses over multiple intensities and locations. Analysis of the recruited neural structures revealed the lack of direct influence of EES on motoneurons and interneurons. Simulations and pharmacological experiments demonstrated that EES engages spinal circuits trans-synaptically through the recruitment of myelinated afferent fibers. The model also predicted the capacity of spatially distinct EES to modulate side-specific limb movements and, to a lesser extent, extension versus flexion. These predictions were confirmed during standing and walking enabled by EES in spinal rats. These combined results provide a mechanistic framework for the design of spinal neuroprosthetic systems to improve standing and walking after neurological disorders.
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28
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Stecina K, Fedirchuk B, Hultborn H. Information to cerebellum on spinal motor networks mediated by the dorsal spinocerebellar tract. J Physiol 2013; 591:5433-43. [PMID: 23613538 DOI: 10.1113/jphysiol.2012.249110] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The main objective of this review is to re-examine the type of information transmitted by the dorsal and ventral spinocerebellar tracts (DSCT and VSCT respectively) during rhythmic motor actions such as locomotion. Based on experiments in the 1960s and 1970s, the DSCT was viewed as a relay of peripheral sensory input to the cerebellum in general, and during rhythmic movements such as locomotion and scratch. In contrast, the VSCT was seen as conveying a copy of the output of spinal neuronal circuitry, including those circuits generating rhythmic motor activity (the spinal central pattern generator, CPG). Emerging anatomical and electrophysiological information on the putative subpopulations of DSCT and VSCT neurons suggest differentiated functions for some of the subpopulations. Multiple lines of evidence support the notion that sensory input is not the only source driving DSCT neurons and, overall, there is a greater similarity between DSCT and VSCT activity than previously acknowledged. Indeed the majority of DSCT cells can be driven by spinal CPGs for locomotion and scratch without phasic sensory input. It thus seems natural to propose the possibility that CPG input to some of these neurons may contribute to distinguishing sensory inputs that are a consequence of the active locomotion from those resulting from perturbations in the external world.
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Affiliation(s)
- Katinka Stecina
- K. Stecina: University of Copenhagen, Department of Neuroscience and Pharmacology, The Panum Institute, 33.3, Blegdamsvej 3, Copenhagen 2200, Denmark.
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Sonner PM, Ladle DR. Early postnatal development of GABAergic presynaptic inhibition of Ia proprioceptive afferent connections in mouse spinal cord. J Neurophysiol 2013; 109:2118-28. [PMID: 23343895 DOI: 10.1152/jn.00783.2012] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Sensory feedback is critical for normal locomotion and adaptation to external perturbations during movement. Feedback provided by group Ia afferents influences motor output both directly through monosynaptic connections and indirectly through spinal interneuronal circuits. For example, the circuit responsible for reciprocal inhibition, which acts to prevent co-contraction of antagonist flexor and extensor muscles, is driven by Ia afferent feedback. Additionally, circuits mediating presynaptic inhibition can limit Ia afferent synaptic transmission onto central neuronal targets in a task-specific manner. These circuits can also be activated by stimulation of proprioceptive afferents. Rodent locomotion rapidly matures during postnatal development; therefore, we assayed the functional status of reciprocal and presynaptic inhibitory circuits of mice at birth and compared responses with observations made after 1 wk of postnatal development. Using extracellular physiological techniques from isolated and hemisected spinal cord preparations, we demonstrate that Ia afferent-evoked reciprocal inhibition is as effective at blocking antagonist motor neuron activation at birth as at 1 wk postnatally. In contrast, at birth conditioning stimulation of muscle nerve afferents failed to evoke presynaptic inhibition sufficient to block functional transmission at synapses between Ia afferents and motor neurons, even though dorsal root potentials could be evoked by stimulating the neighboring dorsal root. Presynaptic inhibition at this synapse was readily observed, however, at the end of the first postnatal week. These results indicate Ia afferent feedback from the periphery to central spinal circuits is only weakly gated at birth, which may provide enhanced sensitivity to peripheral feedback during early postnatal experiences.
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Affiliation(s)
- Patrick M Sonner
- Department of Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, Ohio, USA
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Fedirchuk B, Stecina K, Kristensen KK, Zhang M, Meehan CF, Bennett DJ, Hultborn H. Rhythmic activity of feline dorsal and ventral spinocerebellar tract neurons during fictive motor actions. J Neurophysiol 2012; 109:375-88. [PMID: 23100134 DOI: 10.1152/jn.00649.2012] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Neurons of the dorsal spinocerebellar tracts (DSCT) have been described to be rhythmically active during walking on a treadmill in decerebrate cats, but this activity ceased following deafferentation of the hindlimb. This observation supported the hypothesis that DSCT neurons primarily relay the activity of hindlimb afferents during locomotion, but lack input from the spinal central pattern generator. The ventral spinocerebellar tract (VSCT) neurons, on the other hand, were found to be active during actual locomotion (on a treadmill) even after deafferentation, as well as during fictive locomotion (without phasic afferent feedback). In this study, we compared the activity of DSCT and VSCT neurons during fictive rhythmic motor behaviors. We used decerebrate cat preparations in which fictive motor tasks can be evoked while the animal is paralyzed and there is no rhythmic sensory input from hindlimb nerves. Spinocerebellar tract cells with cell bodies located in the lumbar segments were identified by electrophysiological techniques and examined by extra- and intracellular microelectrode recordings. During fictive locomotion, 57/81 DSCT and 30/30 VSCT neurons showed phasic, cycle-related activity. During fictive scratch, 19/29 DSCT neurons showed activity related to the scratch cycle. We provide evidence for the first time that locomotor and scratch drive potentials are present not only in VSCT, but also in the majority of DSCT neurons. These results demonstrate that both spinocerebellar tracts receive input from the central pattern generator circuitry, often sufficient to elicit firing in the absence of sensory input.
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Affiliation(s)
- Brent Fedirchuk
- University of Manitoba, Department of Physiology, Winnipeg, Manitoba, Canada
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Honeycutt CF, Perreault EJ. Planning of ballistic movement following stroke: insights from the startle reflex. PLoS One 2012; 7:e43097. [PMID: 22952634 PMCID: PMC3431358 DOI: 10.1371/journal.pone.0043097] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2012] [Accepted: 07/17/2012] [Indexed: 11/18/2022] Open
Abstract
Following stroke, reaching movements are slow, segmented, and variable. It is unclear if these deficits result from a poorly constructed movement plan or an inability to voluntarily execute an appropriate plan. The acoustic startle reflex provides a means to initiate a motor plan involuntarily. In the presence of a movement plan, startling acoustic stimulus triggers non-voluntary early execution of planned movement, a phenomenon known as the startReact response. In unimpaired individuals, the startReact response is identical to a voluntarily initiated movement, except that it is elicited 30–40 ms. As the startReact response is thought to be mediated by brainstem pathways, we hypothesized that the startReact response is intact in stroke subjects. If startReact is intact, it may be possible to elicit more task-appropriate patterns of muscle activation than can be elicited voluntarily. We found that startReact responses were intact following stroke. Responses were initiated as rapidly as those in unimpaired subjects, and with muscle coordination patterns resembling those seen during unimpaired volitional movements. Results were striking for elbow flexion movements, which demonstrated no significant differences between the startReact responses elicited in our stroke and unimpaired subject groups. The results during planned extension movements were less straightforward for stroke subjects, since the startReact response exhibited task inappropriate activity in the flexors. This inappropriate activity diminished over time. This adaptation suggests that the inappropriate activity was transient in nature and not related to the underlying movement plan. We hypothesize that the task-inappropriate flexor activity during extension results from an inability to suppress the classic startle reflex, which primarily influences flexor muscles and adapts rapidly with successive stimuli. These results indicate that stroke subjects are capable of planning ballistic elbow movements, and that when these planned movements are involuntarily executed they can be as rapid and appropriate as those in unimpaired individuals.
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Affiliation(s)
- Claire Fletcher Honeycutt
- Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois, United States of America.
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Hatz K, Mombaur K, Donelan JM. Control of ankle extensor muscle activity in walking cats. J Neurophysiol 2012; 108:2785-93. [PMID: 22933727 DOI: 10.1152/jn.00944.2011] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Our objective was to gain insight into the relative importance of feedforward control and different proprioceptive feedback pathways to ongoing ankle extensor activity during walking in the conscious cat. We asked whether the modulation of stance phase muscle activity is due primarily to proprioceptive feedback and whether the same proprioceptive gains and feedforward commands can automatically generate the muscle activity required for changes in walking slope. To test these hypotheses, we analyzed previously collected muscle activity and mechanics data from cats with an isolated medial gastrocnemius muscle walking along a sloped pegway. Models of proprioceptor dynamics predicted afferent activity from the measured muscle mechanics. We modeled muscle activity as the weighted sum of the activity predicted from the different proprioceptive pathways and a simple model of central drive. We determined the unknown model parameters using optimization procedures that minimized the error between the predicted and measured muscle activity. We found that the modulation of muscle activity within the stance phase and across walking slopes is indeed well described by neural control that employs constant central drive and constant proprioceptive feedback gains. Furthermore, it is force feedback from Ib afferents that is primarily responsible for modulating muscle activity; group II afferent feedback makes a small contribution to tonic activity, and Ia afferent feedback makes no contribution. Force feedback combined with tonic central drive appears to provide a simple control mechanism for automatically compensating for changes in terrain without requiring different commands from the brain or even modification of central nervous system gains.
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Affiliation(s)
- Kathrin Hatz
- Interdisciplinary Center for Scientific Computing, Heidelberg University, Heidelberg, Germany
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Inhibition of motoneurons during the cutaneous silent period in the spinal cord of the turtle. Exp Brain Res 2012; 220:23-8. [PMID: 22580573 DOI: 10.1007/s00221-012-3111-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Accepted: 04/26/2012] [Indexed: 02/04/2023]
Abstract
The transient suppression of motor activity in the spinal cord after a cutaneous stimulus is termed the cutaneous silent period (CSP). It is not known if CSP is due to suppression of the premotor network or direct inhibition of motoneurons. This issue was examined by intracellular recordings from motoneurons in the isolated carapace-spinal cord preparation from adult turtles during rhythmic scratch-like reflex. Electrical stimulation of cutaneous nerves induced CSP-like suppression of motor nerve firing during rhythmic network activity. The stimulus that generated the CSP-like suppression of motor activity evokes a polysynaptic compound synaptic potential in motoneurons and suppressed their firing. This compound synaptic potential was hyperpolarizing near threshold for action potentials and was associated with a substantial increase in conductance during the CSP in the motor pool. These results show that direct postsynaptic inhibition of motoneurons contributes to the CSP.
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Hellekes K, Blincow E, Hoffmann J, Büschges A. Control of reflex reversal in stick insect walking: effects of intersegmental signals, changes in direction, and optomotor-induced turning. J Neurophysiol 2012; 107:239-49. [DOI: 10.1152/jn.00718.2011] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In many animals, the effects of sensory feedback on motor output change during locomotion. These changes can occur as reflex reversals in which sense organs that activate muscles to counter perturbations in posture control instead reinforce movements in walking. The mechanisms underlying these changes are only partially understood. As such, it is unclear whether reflex reversals are modulated when locomotion is adapted, such as during changes in walking direction or in turning movements. We investigated these questions in the stick insect Carausius morosus, where sensory signals from the femoral chordotonal organ are known to produce resistance reflexes at rest but assistive movements during walking. We studied how intersegmental signals from neighboring legs affect the generation of reflex reversals in a semi-intact preparation that allows free leg movement during walking. We found that reflex reversal was enhanced by stepping activity of the ipsilateral neighboring rostral leg, whereas stepping of contralateral legs had no effect. Furthermore, we found that the occurrence of reflex reversals was task-specific: in the front legs of animals with five legs walking, reflex reversal was generated only during forward and not backward walking. Similarly, during optomotor-induced curved walking, reflex reversal occurred only in the middle leg on the inside of the turn and not in the contralateral leg on the outside of the turn. Thus our results show for the first time that the nervous system modulates reflexes in individual legs in the adaptation of walking to specific tasks.
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Affiliation(s)
- Katja Hellekes
- Department of Animal Physiology, Zoological Institute, Biocenter Cologne, University of Cologne, Cologne, Germany
| | - Eric Blincow
- Department of Animal Physiology, Zoological Institute, Biocenter Cologne, University of Cologne, Cologne, Germany
| | - Julia Hoffmann
- Department of Animal Physiology, Zoological Institute, Biocenter Cologne, University of Cologne, Cologne, Germany
| | - Ansgar Büschges
- Department of Animal Physiology, Zoological Institute, Biocenter Cologne, University of Cologne, Cologne, Germany
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Van Doornik J, Azevedo Coste C, Ushiba J, Sinkjaer T. Positive afferent feedback to the human soleus muscle during quiet standing. Muscle Nerve 2011; 43:726-32. [PMID: 21462208 DOI: 10.1002/mus.21952] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/20/2010] [Indexed: 11/06/2022]
Abstract
INTRODUCTION In this study we investigated the mechanisms responsible for soleus muscle contraction during quiet standing. METHODS Subjects stood on a platform that was randomly moved forward or downward or rotated around the ankle. RESULTS Downward perturbation caused a short-latency drop in averaged rectified soleus electromyography (SOL EMG). SOL drop increased monotonically with downward acceleration amplitude. Ischemia above the knee abolished or diminished this drop. Ischemia above the ankle had no diminishing effect. Vibration of the Achilles tendon had a diminishing effect on the amplitude of SOL responses. CONCLUSIONS The short-latency drop in SOL observed for downward perturbation might be due to a decrease in positive afferent feedback due to the sudden decrease in body weight. This implies the existence of an ongoing afferent feedback loop toward the SOL motoneuron pool from force-sensitive receptors. Both Ia and Ib afferents probably play a role in the responses observed.
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Affiliation(s)
- Johan Van Doornik
- Center for Sensory Motor Interaction, Aalborg University, Aalborg, Denmark
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36
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Lewek MD. The influence of body weight support on ankle mechanics during treadmill walking. J Biomech 2010; 44:128-33. [PMID: 20855074 DOI: 10.1016/j.jbiomech.2010.08.037] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2010] [Revised: 07/16/2010] [Accepted: 08/29/2010] [Indexed: 10/19/2022]
Abstract
The use of body weight support (BWS) systems during locomotor retraining has become routine in clinical settings. BWS alters load receptor feedback, however, and may alter the biomechanical role of the ankle plantarflexors, influencing gait. The purpose of this study was to characterize the biomechanical adaptations that occur as a result of a change in limb load (controlled indirectly through BWS) and gait speed during treadmill locomotion. Fifteen unimpaired participants underwent gait analysis with surface electromyography while walking on an instrumented dual-belt treadmill at seven different speeds (ranging from 0.4 to 1.6m/s) and three BWS conditions (ranging from 0% to 40% BWS). While walking, spatiotemporal measures, anterior/posterior ground reaction forces, and ankle kinetics and muscle activity were measured and compared between conditions. At slower gait speeds, propulsive forces and ankle kinetics were unaffected by changing BWS; however, at gait speeds ≥ approximately 0.8m/s, an increase in BWS yielded reduced propulsive forces and diminished ankle plantarflexor moments and powers. Muscle activity remained unaltered by changing BWS across all gait speeds. The use of BWS could provide the advantage of faster walking speeds with the same push-off forces as required of a slower speed. While the use of BWS at slower speeds does not appear to detrimentally affect gait, it may be important to reduce BWS as participants progress with training, to encourage maximal push-off forces. The reduction in plantarflexor kinetics at higher speeds suggests that the use of BWS in higher functioning individuals may impair the ability to relearn walking.
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Affiliation(s)
- Michael D Lewek
- Department of Allied Health Sciences, Division of Physical Therapy, University of North Carolina, Chapel Hill, 3043 Bondurant Hall, CB#7135, NC 27599-7135, USA.
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Liu TT, Bannatyne BA, Jankowska E, Maxwell DJ. Properties of axon terminals contacting intermediate zone excitatory and inhibitory premotor interneurons with monosynaptic input from group I and II muscle afferents. J Physiol 2010; 588:4217-33. [PMID: 20837640 DOI: 10.1113/jphysiol.2010.192211] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The intermediate zone of the spinal grey matter contains premotor interneurons mediating reflex actions of group I and II muscle afferents. However, limited information is available on how activity of inhibitory versus excitatory interneurons in this population are modulated and how they contribute to motor networks. There were three aims of this study: (1) to characterize excitatory axonal contacts on interneurons; (2) to determine if contact patterns on excitatory and inhibitory interneurons are different; (3) to determine if there are differences in presynaptic inhibitory control of excitatory and inhibitory interneurons. We used intracellular labelling of electrophysiologically identified cells along with immunochemistry to characterise contacts formed by axons that contain vesicular glutamate transporters (VGLUT1 and VGLUT2) and contacts formed by VGLUT1 terminals which in turn were contacted by GABAergic terminals on cells that were characterised according to their transmitter phenotype. All 17 cells investigated were associated with numerous VGLUT1 contacts originating from primary afferents, and similar contact densities were found on excitatory and inhibitory cells, but VGLUT2-immunoreactive terminals originating from intraspinal neurons were less frequent, or were practically absent, especially on excitatory cells. Similar numbers of VGLUT1 contacts with associated GABAergic terminals were found on excitatory and inhibitory cells indicating a similar extent of presynaptic GABAergic control. However, scarce VGLUT2 terminals on intermediate zone excitatory premotor interneurons with input from muscle afferents suggest that they are not significantly excited by other spinal neurons but are under direct excitatory control of supraspinal neurons and, principally inhibitory, control of spinal neurons.
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Affiliation(s)
- Ting Ting Liu
- Spinal Cord Group, Institute of Neuroscience and Psychology, College of Medicine, Veterinary Medicine and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK
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Jankowska E, Edgley SA. Functional subdivision of feline spinal interneurons in reflex pathways from group Ib and II muscle afferents; an update. Eur J Neurosci 2010; 32:881-93. [PMID: 20722720 DOI: 10.1111/j.1460-9568.2010.07354.x] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
A first step towards understanding the operation of a neural network is identification of the populations of neurons that contribute to it. Our aim here is to reassess the basis for subdivision of adult mammalian spinal interneurons that mediate reflex actions from tendon organs (group Ib afferents) and muscle spindle secondary endings (group II afferents) into separate populations. Re-examining the existing experimental data, we find no compelling reasons to consider intermediate zone interneurons with input from group Ib afferents to be distinct from those co-excited by group II afferents. Similar patterns of distributed input have been found in subpopulations that project ipsilaterally, contralaterally or bilaterally, and in both excitatory and inhibitory interneurons; differences in input from group I and II afferents to individual interneurons showed intra- rather than inter-population variation. Patterns of reflex actions evoked from group Ib and II afferents and task-dependent changes in these actions, e.g. during locomotion, may likewise be compatible with mediation by premotor interneurons integrating information from both group I and II afferents. Pathological changes after injuries of the central nervous system in humans and the lineage of different subclasses of embryonic interneurons may therefore be analyzed without need to consider subdivision of adult intermediate zone interneurons into subpopulations with group Ib or group II input. We propose renaming these neurons 'group I/II interneurons'.
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Affiliation(s)
- Elzbieta Jankowska
- Department of Physiology and Neuroscience, Sahlgrenska Academy, University of Gothenburg, 405 30 Göteborg, Sweden.
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Gordon KE, Wu M, Kahn JH, Schmit BD. Feedback and feedforward locomotor adaptations to ankle-foot load in people with incomplete spinal cord injury. J Neurophysiol 2010; 104:1325-38. [PMID: 20573970 DOI: 10.1152/jn.00604.2009] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Humans with spinal cord injury (SCI) modulate locomotor output in response to limb load. Understanding the neural control mechanisms responsible for locomotor adaptation could provide a framework for selecting effective interventions. We quantified feedback and feedforward locomotor adaptations to limb load modulations in people with incomplete SCI. While subjects airstepped (stepping performed with kinematic assistance and 100% bodyweight support), a powered-orthosis created a dorisflexor torque during the "stance phase" of select steps producing highly controlled ankle-load perturbations. When given repetitive, stance phase ankle-load, the increase in hip extension work, 0.27 J/kg above baseline (no ankle-load airstepping), was greater than the response to ankle-load applied during a single step, 0.14 J/kg (P = 0.029). This finding suggests that, at the hip, subjects produced both feedforward and feedback locomotor modulations. We estimate that, at the hip, the locomotor response to repetitive ankle-load was modulated almost equally by ongoing feedback and feedforward adaptations. The majority of subjects also showed after-effects in hip kinetic patterns that lasted 3 min in response to repetitive loading, providing additional evidence of feedforward locomotor adaptations. The magnitude of the after-effect was proportional to the response to repetitive ankle-foot load (R(2) = 0.92). In contrast, increases in soleus EMG amplitude were not different during repetitive and single-step ankle-load exposure, suggesting that ankle locomotor modulations were predominately feedback-based. Although subjects made both feedback and feedforward locomotor adaptations to changes in ankle-load, between-subject variations suggest that walking function may be related to the ability to make feedforward adaptations.
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Affiliation(s)
- Keith E Gordon
- Sensory Motor Performance Program, Rehabilitation Inst. of Chicago, 345 E. Superior St., Rm. 1406, Chicago, IL 60611, USA.
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Genetically defined inhibitory neurons in the mouse spinal cord dorsal horn: a possible source of rhythmic inhibition of motoneurons during fictive locomotion. J Neurosci 2010; 30:1137-48. [PMID: 20089922 DOI: 10.1523/jneurosci.1401-09.2010] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
To ensure alternation of flexor and extensor muscles during locomotion, the spinal locomotor network provides rhythmic inhibition to motoneurons. The source of this inhibition in mammals is incompletely defined. We have identified a population of GABAergic interneurons located in medial laminae V/VI that express green fluorescent protein (GFP) in glutamic acid decarboxylase-65::GFP transgenic mice. Immunohistochemical studies revealed GFP+ terminals in apposition to motoneuronal somata, neurons in Clarke's column, and in laminae V/VI where they apposed GFP+ interneurons, thus forming putative reciprocal connections. Whole-cell patch-clamp recordings from GFP+ interneurons in spinal cord slices revealed a range of electrophysiological profiles, including sag and postinhibitory rebound potentials. Most neurons fired tonically in response to depolarizing current injection. Calcium transients demonstrated by two-photon excitation microscopy in the hemisected spinal cord were recorded in response to low-threshold dorsal root stimulation, indicating these neurons receive primary afferent input. Following a locomotor task, the number of GFP+ neurons expressing Fos increased, indicating that these neurons are active during locomotion. During fictive locomotion induced in the hemisected spinal cord, two-photon excitation imaging demonstrated rhythmic calcium activity in these interneurons, which correlated with the termination of ventral root bursts. We suggest that these dorsomedial GABAergic interneurons are involved in spinal locomotor networks, and may provide direct rhythmic inhibitory input to motoneurons during locomotion.
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Frigon A, Sirois J, Gossard JP. Effects of ankle and hip muscle afferent inputs on rhythm generation during fictive locomotion. J Neurophysiol 2010; 103:1591-605. [PMID: 20089809 DOI: 10.1152/jn.01028.2009] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hip position and loading of limb extensors are major sensory cues for the initiation and duration of different phases during walking. Although these inputs have pathways projecting to the locomotor rhythm generator, their effects may vary in different parts of the locomotor cycle. In the present study, the plantaris (Pl), sartorius (Sart), rectus femoris (RF), and caudal gluteal (cGlu) nerves were stimulated at group I and/or group II strength during spontaneous fictive locomotion in 16 adult decerebrate cats. These nerves supply muscles that extend the ankle (Pl), flex the hip (Sart, RF), or extend the hip (cGlu). Stimuli were given at six epochs of the locomotor cycle to evaluate when they access the rhythm generator. Group I afferents from Pl nerve always reset the locomotor rhythm; stimulation during extension prolonged cycle period and extension phase duration, while stimulation during flexion terminated flexion and initiated extension. On the other hand, stimulating RF and cGlu nerves only produced significant effects on the rhythm in precise epochs, particularly during mid-flexion and/or mid- to late extension. Stimulating the Sart nerve produced complex effects on the rhythm that were not distributed evenly to all extensor motor pools. The most consistent effect was reduced flexion phase duration with stimulation during flexion, particularly at group II strength, and prolongation of the extension phase but only in late extension. That hip muscle afferents reset the rhythm in only specific epochs of the locomotor cycle suggests that the rhythm generator operates with several subdivisions to determine phase and cycle durations.
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Affiliation(s)
- Alain Frigon
- Groupe de Recherche sur le Système Nerveux Central des Fonds de la Recherche en Santé du Québec, Département de Physiologie, Université de Montréal, Montréal, Québec, Canada
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Brownstone RM, Bui TV. Spinal interneurons providing input to the final common path during locomotion. PROGRESS IN BRAIN RESEARCH 2010; 187:81-95. [PMID: 21111202 DOI: 10.1016/b978-0-444-53613-6.00006-x] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
As the nexus between the nervous system and the skeletomuscular system, motoneurons effect all behavior. As such, motoneuron activity must be well regulated so as to generate appropriately timed and graded muscular contractions. Accordingly, motoneurons receive a large number of both excitatory and inhibitory synaptic inputs from various peripheral and central sources. Many of these synaptic contacts arise from spinal interneurons, some of which belong to spinal networks responsible for the generation of locomotor activity. Although the complete definition of these networks remains elusive, it is known that the neural machinery necessary to generate the basic rhythm and pattern of locomotion is contained within the spinal cord. One approach to gaining insights into spinal locomotor networks is to describe those spinal interneurons that directly control the activity of motoneurons, so-called last-order interneurons. In this chapter, we briefly survey the different populations of last-order interneurons that have been identified using anatomical, physiological, and genetic methodologies. We discuss the possible roles of these identified last-order interneurons in generating locomotor activity, and in the process, identify particular criteria that may be useful in identifying putative last-order interneurons belonging to spinal locomotor networks.
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Affiliation(s)
- Robert M Brownstone
- Department of Surgery (Neurosurgery), Dalhousie University, Halifax, Nova Scotia, Canada
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43
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Honeycutt CF, Gottschall JS, Nichols TR. Electromyographic responses from the hindlimb muscles of the decerebrate cat to horizontal support surface perturbations. J Neurophysiol 2009; 101:2751-61. [PMID: 19321638 DOI: 10.1152/jn.91040.2008] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The sensory and neural mechanisms underlying postural control have received much attention in recent decades but remain poorly understood. Our objectives were 1) to establish the decerebrate cat as an appropriate model for further research into the sensory mechanisms of postural control and 2) to observe what elements of the postural response can be generated by the brain stem and spinal cord. Ten animals were decerebrated using a modified premammillary technique, which consists of a premammillary decerebration that is modified with a vertical transection near the subthalamic nucleus to eliminate spontaneous locomotion. Horizontal support surface perturbations were applied to all four limbs and electromyographic recordings were collected from 14 muscles of the right hindlimb. Muscle activation was quantified with tuning curves, which compared increases and decreases in muscle activity to background and graphed the difference against perturbation direction. Parallels were drawn between these tuning curves, which were further quantified with a principal direction and breadth (range of directions of muscle activation), and data collected by other researchers from the intact animal. We found a strong similarity in the direction and breadth of the tuning curves generated in the decerebrate and intact cat. These results support our hypothesis that directionally specific tuning of muscles in response to support surface perturbations does not require the cortex, further indicating a strong role for the brain stem and spinal cord circuits in mediating directionally appropriate muscle activation patterns.
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Affiliation(s)
- Claire F Honeycutt
- Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332-0356, USA
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The implications of force feedback for the lambda model. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2009; 629:663-79. [PMID: 19227527 DOI: 10.1007/978-0-387-77064-2_36] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
Abstract
It is argued here that length and force feedback play important but distinct roles in motor coordination. Length feedback compensates for several nonlinear properties of muscle and therefore simplifies its behavior, but in addition promotes the nonlinear relationship between force and stiffness that is essential to the mechanism for modulating joint stiffness. Excitatory force feedback is also primarily autogenic. Under conditions of level treadmill stepping in cat walking, positive force feedback is restricted in the distal hindlimb to a few and perhaps only one ankle extensor, the gastrocnemius muscle group. Based on the anatomy of this group, positive force feedback provides a stiff linkage that reinforces proportional coordination between ankle and knee joints. In terms of the lambda model, excitatory force feedback can reinforce muscular force generation and stiffness, but should have no significant effect on activation threshold. Inhibitory force feedback projects mainly to muscles that span different joints and axes of rotation than the parent muscle. This heterogenic force feedback is thought to promote interjoint coordination and thought to influence stiffness of the joints and limbs. During locomotion, the inhibitory influences appear to be focused on the distal musculature. Since the inhibitory force feedback is heterogenic, it also influences the threshold for activation of relevant musculature. Threshold is therefore not entirely a control variable and independent of feedback. It is proposed that the actuators for movement consist of systems of muscles or motor units that are linked by feedback and that receive control signals from elsewhere in the nervous system.
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Donelan JM, McVea DA, Pearson KG. Force Regulation of Ankle Extensor Muscle Activity in Freely Walking Cats. J Neurophysiol 2009; 101:360-71. [DOI: 10.1152/jn.90918.2008] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To gain insight into the relative importance of force feedback to ongoing ankle extensor activity during walking in the conscious cat, we isolated the medial gastrocnemius muscle (MG) by denervating the other ankle extensors and measured the magnitude of its activity at different muscle lengths, velocities, and forces accomplished by having the animals walk up and down a sloped pegway. Mathematical models of proprioceptor dynamics predicted afferent activity and revealed that the changes in muscle activity under our experimental conditions were strongly correlated with Ib activity and not consistently associated with changes in Ia or group II activity. This allowed us to determine the gains within the force feedback pathway using a simple model of the neuromuscular system and the measured relationship between MG activity and force. Loop gain increased with muscle length due to the intrinsic force–length property of muscle. The gain of the pathway that converts muscle force to motoneuron depolarization was independent of length. To better test for a causal relationship between modulation of force feedback and changes in muscle activity, a second set of experiments was performed in which the MG muscle was perturbed during ground contact of the hind foot by dropping or lifting the peg underfoot. Collectively, these investigations support a causal role for force feedback and indicate that about 30% of the total muscle activity is due to force feedback during level walking. Force feedback's role increases during upslope walking and decreases during downslope walking, providing a simple mechanism for compensating for changes in terrain.
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Bannatyne BA, Liu TT, Hammar I, Stecina K, Jankowska E, Maxwell DJ. Excitatory and inhibitory intermediate zone interneurons in pathways from feline group I and II afferents: differences in axonal projections and input. J Physiol 2008; 587:379-99. [PMID: 19047211 DOI: 10.1113/jphysiol.2008.159129] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The aim of the present study was to compare properties of excitatory and inhibitory spinal intermediate zone interneurons in pathways from group I and II muscle afferents in the cat. Interneurons were labelled intracellularly and their transmitter phenotypes were defined by using immunocytochemistry. In total 14 glutamatergic, 22 glycinergic and 2 GABAergic/glycinergic interneurons were retrieved. All interneurons were located in laminae V-VII of the L3-L7 segments. No consistent differences were found in the location, the soma sizes or the extent of the dendritic trees of excitatory and inhibitory interneurons. However, major differences were found in their axonal projections; excitatory interneurons projected either ipsilaterally, bilaterally or contralaterally, while inhibitory interneurons projected exclusively ipsilaterally. Terminal projections of glycinergic and glutamatergic cells were found within motor nuclei as well as other regions of the grey matter which include the intermediate region, laminae VII and VIII. Cells containing GABA/glycine had more restricted projections, principally within the intermediate zone where they formed appositions with glutamatergic axon terminals and unidentified cells and therefore are likely to be involved in presynaptic as well as postsynaptic inhibition. The majority of excitatory and inhibitory interneurons were found to be coexcited by group I and II afferents (monosynaptically) and by reticulospinal neurons (mono- or disynaptically) and to integrate information from several muscles. Taken together the morphological and electrophysiological data show that individual excitatory and inhibitory intermediate zone interneurons may operate in a highly differentiated way and thereby contribute to a variety of motor synergies.
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Affiliation(s)
- B A Bannatyne
- Spinal Cord Group, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, UK.
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Duysens J, Beerepoot V, Veltink P, Weerdesteyn V, Smits-Engelsman B. Proprioceptive perturbations of stability during gait. Neurophysiol Clin 2008; 38:399-410. [DOI: 10.1016/j.neucli.2008.09.010] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2008] [Accepted: 09/22/2008] [Indexed: 11/25/2022] Open
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Ross KT, Nichols TR. Heterogenic feedback between hindlimb extensors in the spontaneously locomoting premammillary cat. J Neurophysiol 2008; 101:184-97. [PMID: 19005003 DOI: 10.1152/jn.90338.2008] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Electrophysiological studies in anesthetized animals have revealed that pathways carrying force information from Golgi tendon organs in antigravity muscles mediate widespread inhibition among other antigravity muscles in the feline hindlimb. More recent evidence in paralyzed or nonparalyzed decerebrate cats has shown that some inhibitory pathways are suppressed and separate excitatory pathways from Golgi tendon organ afferents are opened on the transition from steady force production to locomotor activity. To obtain additional insight into the functions of these pathways during locomotion, we investigated the distribution of force-dependent inhibition and excitation during spontaneous locomotion and during constant force exertion in the premammillary decerebrate cat. We used four servo-controlled stretching devices to apply controlled stretches in various combinations to the gastrocnemius muscles (G), plantaris muscle (PLAN), flexor hallucis longus muscle (FHL), and quadriceps muscles (QUADS) during treadmill stepping and the crossed-extension reflex (XER). We recorded the force responses from the same muscles and were therefore able to evaluate autogenic (intramuscular) and heterogenic (intermuscular) reflexes among this set of muscles. In previous studies using the intercollicular decerebrate cat, heterogenic inhibition among QUADS, G, FHL, and PLAN was bidirectional. During treadmill stepping, heterogenic feedback from QUADS onto G and G onto PLAN and FHL remained inhibitory and was force-dependent. However, heterogenic inhibition from PLAN and FHL onto G, and from G onto QUADS, was weaker than during the XER. We propose that pathways mediating heterogenic inhibition may remain inhibitory under some forms of locomotion on a level surface but that the strengths of these pathways change to result in a proximal to distal gradient of inhibition. The potential contributions of heterogenic inhibition to interjoint coordination and limb stability are discussed.
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Affiliation(s)
- Kyla T Ross
- Department of Biomedical Engineering, Georgia Institute of Technology, 313 Ferst Dr., Atlanta, GA 30332, USA.
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Dorofeev IY, Avelev VD, Shcherbakova NA, Gerasimenko YP. The role of cutaneous afferents in controlling locomotion evoked by epidural stimulation of the spinal cord in decerebrate cats. ACTA ACUST UNITED AC 2008; 38:695-701. [PMID: 18720012 DOI: 10.1007/s11055-008-9034-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2007] [Revised: 05/16/2007] [Indexed: 11/26/2022]
Abstract
The effects of the cutaneous input on the formation of the locomotor pattern in conditions of epidural stimulation of the spinal cord in decerebrate cats were studied. Locomotor activity was induced by rhythmic stimulation of the dorsal surface of spinal cord segments L4-L5 at a frequency of 3-5 Hz. Electromyograms (EMG) recorded from the antagonist muscles quadriceps, semitendinosus, tibialis anterior, and gastrocnemius lateralis were recorded, along with the kinematics of stepping movements during locomotion on a moving treadmill and reflex responses to single stimuli. Changes in the pattern of reactions observed before and after exclusion of cutaneous receptors (infiltration of lidocaine solution at the base of the paw or irrigation of the paw pads with chlorothane solution) were assessed. This treatment led to impairment of the locomotor cycle: the paw was placed with the rear surface downward and was dragged along in the swing phase, and the duration of the stance phase decreased. Exclusion of cutaneous afferents suppressed the polysynaptic activity of the extensor muscles and the distal flexor muscle of the ipsilateral hindlimb during locomotion evoked by epidural stimulation of the spinal cord. The effects of exclusion of cutaneous afferents on the monosynaptic component of the EMG response were insignificant.
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Affiliation(s)
- I Yu Dorofeev
- I. P. Pavlov Institute of Physiology, Russian Academy of Sciences, 6 Makarov Bank, 199034 St. Petersburg, Russia
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Plasticity of interneuronal networks of the functionally isolated human spinal cord. ACTA ACUST UNITED AC 2007; 57:255-64. [PMID: 18042493 DOI: 10.1016/j.brainresrev.2007.07.012] [Citation(s) in RCA: 128] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2007] [Accepted: 07/19/2007] [Indexed: 11/20/2022]
Abstract
The loss of walking after human spinal cord injury has been attributed to the dominance of supraspinal over spinal mechanisms. The evidence for central pattern generation in humans is limited due to the inability to conclusively isolate the circuitry from descending and afferent input. However, studying individuals following spinal cord injury with no detectable influence on spinal networks from supraspinal centers can provide insight to their interaction with afferent input. The focus of this article is on the interaction of sensory input with human spinal networks in the generation of locomotor patterns. The functionally isolated human spinal cord has the capacity to generate locomotor patterns with appropriate afferent input. Locomotor Training is a rehabilitative strategy that has evolved from animal and humans studies focused on the neural plasticity of the spinal cord and has been successful for many people with acute and chronic incomplete spinal cord injury. However, even those individuals with clinically complete spinal cord injury that generate appropriate locomotor patterns during stepping with assistance on a treadmill with body weight support cannot sustain overground walking. This suggests that although a significant control of locomotion can occur at the level of spinal interneuronal networks the level of sustainable excitability of these circuits is still compromised. Future studies should focus on approaches to increase the central state of excitability and may include neural repair strategies, pharmacological interventions or epidural stimulation in combination with Locomotor Training.
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