Disynaptic reciprocal inhibition of ankle extensors in spastic patients

Short- and long-latency contributions to reciprocal inhibition during various levels of muscle contraction of individuals with cerebral palsy

Deficits in reciprocal inhibition likely contribute to excessive antagonist muscle cocontraction during voluntary movements of individuals with cerebral palsy. This study examined neural contributions to reciprocal inhibition of the soleus motoneurons of individuals with spastic, diplegic cerebral palsy and nondisabled individuals during various levels of voluntary tibialis anterior contraction. A condition-test H-reflex paradigm examined short- and long-latency contributions to reciprocal inhibition of soleus neural pools during changing levels of voluntary tibialis anterior contraction. Electrically induced short- and long-latency inhibition was similar between healthy, neurologically intact control subjects and subjects with cerebral palsy during rest. With increasing levels of tibialis anterior contraction, control subjects experienced increasing levels of soleus motoneuron inhibition, especially of long-latency inhibitory responses. In contrast, there was no evidence of modulation of short- or long-latency inhibition with increasing levels of tibialis anterior contraction among subjects with cerebral palsy. Deficits in long-latency (presynaptic) inhibition appear to contribute prominently to voluntary movement impairment of individuals with cerebral palsy.

Spinal reflexes, mechanisms and concepts: From Eccles to Lundberg and beyond

This review focuses on investigations by Sir John Eccles and co-workers in Canberra, AUS in the 1950s, in which they used intracellular recordings to unravel the organization of neuronal networks in the cat spinal cord. Five classical spinal reflexes are emphasized: recurrent inhibition of motoneurons via motor axon collaterals and Renshaw cells, pathways from muscle spindles and Golgi tendon organs, presynaptic inhibition, and the flexor reflex. To set the scene for these major achievements I first provide a brief account of the understanding of the spinal cord in "reflex" and "voluntary" motor activities from the beginning of the 20th century. Next, subsequent work is reviewed on the convergence on spinal interneurons from segmental sensory afferents and descending motor pathways, much of which was performed and inspired by Anders Lundberg's group in Gothenburg, SWE. This work was the keystone for new hypotheses on the role of spinal circuits in normal motor control. Such hypotheses were later tested under more natural conditions; either by recording directly from interneurons in reduced animal preparations or by use of indirect non-invasive techniques in humans performing normal movements. Some of this latter work is also reviewed. These developments would not have been possible without the preceding work on spinal reflexes by Eccles and Lundberg. Finally, there is discussion of how Eccles' work on spinal reflexes remains central (1) as new techniques are introduced on direct recording from interneurons in behaving animals; (2) in experiments on plastic neuronal changes in relation to motor learning and neurorehabilitation; (3) in experiments on transgenic animals uncovering aspects of human pathophysiology; and (4) in evaluating the function of genetically identified classes of neurons in studies on the development of the spinal cord.

Functional plasticity following spinal cord lesions

Spinal cord injury results in marked modification and reorganization of several reflex pathways caudal to the injury. The sudden loss or disruption of descending input engenders substantial changes at the level of primary afferents, interneurons, and motoneurons thus dramatically influencing sensorimotor interactions in the spinal cord. As a general rule reflexes are initially depressed following spinal cord injury due to severe reductions in motoneuron excitability but recover and in some instances become exaggerated. It is thought that modified inhibitory connections and/or altered transmission in some of these reflex pathways after spinal injury as well as the recovery and enhancement of membrane properties in motoneurons underlie several symptoms such as spasticity and may explain some characteristics of spinal locomotion observed in spinally transected animals. Indeed, after partial or complete spinal lesions at the last thoracic vertebra cats recover locomotion when the hindlimbs are placed on a treadmill. Although some deficits in spinal locomotion are related to lesion of specific descending motor pathways, other characteristics can also be explained by changes in the excitability of reflex pathways mentioned above. Consequently it may be the case that to reestablish a stable walking pattern that modified afferent inflow to the spinal cord incurred after injury must be normalized to enable a more normal re-expression of locomotor rhythm generating networks. Indeed, recent evidence demonstrates that step training, which has extensively been shown to facilitate and ameliorate locomotor recovery in spinal animals, directly influences transmission in simple reflex pathways after complete spinal lesions.

Effects of neuromuscular electrical stimulation treatment of cerebral palsy on potential impairment mechanisms: a pilot study

PURPOSE

This pilot study examined the effects of neuromuscular electrical stimulation (NMES) therapy on upper limb impairment in children with cerebral palsy, specifically addressing spasticity, heightened passive resistance to wrist rotation, coactivation, and weakness.

METHODS

Eight subjects, aged five to 15 years, with spastic hemiparesis subsequent to brain injury, participated in three months of NMES therapy, targeting the wrist flexor and extensor muscles. Maximum voluntary wrist extension range of motion against gravity, spasticity, passive torque, maximum voluntary isometric torque, and coactivation were recorded prior to, during, and at the conclusion of the therapy.

RESULTS

Seven of the eight subjects demonstrated a significant (>15 degrees) improvement in wrist extension range of motion against gravity following the NMES treatment, with an average gain of 38 degrees. Differences in spasticity (0.01 +/- 0.14 N-m, p = 0.80) and passive torque (0.03 +/- 0.11 N-m, p = 0.52) were not significant for these subjects. Isometric wrist extension torque, however, did increase significantly (p < 0.01), accompanied by a reduction in flexor coactivation (p < 0.01).

CONCLUSIONS

Evidence suggests that the NMES treatment protocol affected wrist extension by improving the strength of the wrist extensor muscles, possibly through decreased flexor coactivation. Further studies are required, however, to determine whether electrical stimulation itself or other facets of the therapy paradigm played the key role in improvement.

Short-term effects of functional electrical stimulation on spinal excitatory and inhibitory reflexes in ankle extensor and flexor muscles

The purpose of this study was to investigate short-term effects of walking with functional electrical stimulation (FES) on inhibitory and excitatory spinal reflexes in healthy subjects. The FES was applied to the common peroneal (CP) nerve during the swing phase of the step cycle when the ankle flexors are active. We have previously shown that corticospinal excitability for the tibialis anterior (TA) muscle increased after 30 min of FES-assisted walking. An increase of corticospinal excitability could be due to the changes in spinal and/or cortical excitability. Thus, we wished to examine whether a short-term application of FES would increase spinal motoneuronal excitability. Changes could also result from effects on inhibitory as well as excitatory pathways, but to our knowledge no studies have investigated short-term effects of FES on spinal inhibitory pathways. Therefore, we measured reciprocal and presynaptic inhibition, as well as reflex excitability, before and after FES-assisted walking. As controls, effects of FES-like stimulation at rest and walking without stimulation were tested in separate sessions. The TA H-reflex amplitude did not increase after FES in any of the conditions tested, so we have no evidence that FES increases spinal excitability for the TA. The soleus H-reflex decreased slightly (10%) after FES-assisted walking, and remained decreased for at least 30 min. However, the control experiment indicated that this decrease was associated with walking and not with stimulation. Thirty minutes of FES did not produce any significant effects on spinal inhibitory pathways examined in the present study. In conclusion, the soleus H-reflex showed a small but consistent decrease and no spinal circuits examined showed an increase, as was observed in the corticospinal excitability. Thus, we suggest that a short-term application of FES increases the excitability of the cortex or its connections to the spinal cord more effectively than that of spinal pathways.

The evidence for nitric oxide synthase immunopositivity in the monosynaptic Ia-motoneuron pathway of the dog

In this study, nitric oxide synthase immunohistochemistry supported by nicotinamide adenine dinucleotide phosphate diaphorase histochemistry was used to demonstrate the nitric oxide synthase immunoreactivity in the monosynaptic Ia-motoneuron pathway exemplified by structural components of the afferent limb of the soleus H-reflex in the dog. A noticeable number of medium-sized intensely nitric oxide synthase immunoreactive somata (1000-2000 microm(2) square area) and large intraganglionic nitric oxide synthase immunoreactive fibers, presumed to be Ia axons, was found in the L7 and S1 dorsal root ganglia. The existence of nitric oxide synthase immunoreactive fibers (6-8 microm in diameter, not counting the myelin sheath) was confirmed in L7 and S1 dorsal roots and in the medial bundle of both dorsal roots before entering the dorsal root entry zone. By virtue of the funicular organization of nitric oxide synthase immunoreactive fibers in the dorsal funiculus, the largest nitric oxide synthase immunoreactive fibers represent stem Ia axons located in the deep portion of the dorsal funiculus close to the dorsomedial margin of the dorsal horn. Upon entering the gray matter of L7 and S1 segments and passing through the medial half of the dorsal horn, tapered nitric oxide synthase immunoreactive collaterals of the stem Ia fibers pass through the deep layers of the dorsal horn and intermediate zone, and terminate in the group of homonymous motoneurons in L7 and S1 segments innervating the gastrocnemius-soleus muscles. Terminal fibers issued in the ventral horn intensely nitric oxide synthase immunoreactive terminals with long axis ranging from 0.7 to >or=15.1 microm presumed to be Ia bNOS-IR boutons. This finding is unique in that it focuses directly on nitric oxide synthase immunopositivity in the signalling transmitted by proprioceptive Ia fibers. Nitric oxide synthase immunoreactive boutons were found in the neuropil of Clarke's column of L4 segment, varying greatly in size from 0.7 to >or=15.1 microm in length x 0.7 to 4.8 microm wide. Subsequent to identification of the afferent nitric oxide synthase immunoreactive limb of the monosynaptic Ia-motoneuron pathway on control sections, intramuscular injections of the retrograde tracer Fluorogold into the gastrocnemius-soleus muscles, combined with nitric oxide synthase immunohistochemistry of L7 and S1 dorsal root ganglia, confirmed the existence of a number of medium-sized nitric oxide synthase immunoreactive somata (1000-2000 microm(2) square area) in the dorsolateral part of both dorsal root ganglia, presumed to be proprioceptive Ia neurons. Concurrently, large nitric oxide synthase immunoreactive fibers were detected at the input and output side of both dorsal root ganglia. S1 and S2 dorsal rhizotomy caused a marked depletion of nitric oxide synthase immunoreactivity in the medial bundle of S1 and S2 dorsal roots and in the dorsal funiculus of S1, S2 and lower lumbar segments. In addition, anterograde degeneration of large nitric oxide synthase immunoreactive Ia fibers in the dorsal funiculus of L7-S2 segments produces direct evidence that the afferent limb of the soleus H-reflex is nitric oxide synthase immunoreactive and presents new immunohistochemical characteristics of the monosynaptic Ia-motoneuron pathway, unseparably coupled with the performance of the stretch reflex.

Locomotor Training Approaches for Individuals with Spinal Cord Injury

BACKGROUND AND PURPOSE

Body weight supported (BWS) locomotor training improves overground walking ability in individuals with motor-incomplete spinal cord injury (SCI). While there are various approaches available for locomotor training, there is no consensus regarding which of these is optimal. The purpose of this ongoing investigation is to compare outcomes associated with these different training approaches.

SUBJECTS AND METHODS

Twenty-seven subjects with chronic motor-incomplete SCI have completed training and initial and final testing at the time of this preliminary report. Subjects were randomly assigned to 1 of 4 different BWS assisted-stepping groups, including: (1) treadmill training with manual assistance (TM), (2) treadmill training with stimulation (TS), (3) overground training with stimulation (OG), or (4) treadmill training with robotic assistance (LR). Prior to and following participation we assessed walking-related outcome measures including overground walking speed, training speed, step length, and step symmetry.

RESULTS

Data pooled across all subject groups showed a significant effect of training on walking speed. While the differences between groups were not statistically significant, there was a trend toward greater improvement in the TS and OG groups. Post hoc subgroup analysis of outcomes from subjects with slower initial walking speed (< 0.1 m/s; n = 15) compared to those with faster initial walking speeds (> or = 0.1 m/s; n = 12) identified meaningful differences in outcomes with walking speed increasing by 85% in the slower group and by only 9% in the faster group. Step length of both stronger and weaker limb increased in all groups with the exception of those in the LR group. Step symmetry was increased in the TM and LR groups.

DISCUSSION AND CONCLUSION

These results represent preliminary findings of changes in walking-related function associated with different forms of BWS locomotor training for individuals with chronic, motor-incomplete SCI. Early data indicates that locomotor outcomes in these individuals appear to be comparable across training approaches. For the individuals in this study sample, those with the greatest deficits in walking function benefitted the most from locomotor training.

The effect of penile vibratory stimulation on male fertility potential, spasticity and neurogenic detrusor overactivity in spinal cord lesioned individuals

PURPOSE

Present the possibility for treatment of male infertility, spasticity, and neurogenic detrusor overactivity in spinal cord lesioned (SCL) individuals with penile vibratory stimulation (PVS).

METHOD

Obtaining reflex-ejaculation by PVS, by using a vibrator developed for this purpose. The stimulation was performed with a vibrating disc of hard plastic placed against the frenulum of the penis (amplitude > or = 2.5 mm). The vibration continued until antegrade ejaculation or for a maximum of 3 minutes followed by a pause of 1 minute before the cycle was repeated, maximally 4 times.

RESULTS

>80% SCL men are able to obtain ejaculation with PVS. Pregnancy rates obtained with home PVS and intra-vaginal insemination was 22-62% (4 studies), and with PVS or electroejaculation and intrauterine insemination/in-vitro fertilization/intracytoplasmatic sperm injection 39-64% (9 studies). PVS was demonstrated to decrease spasticity significantly when measured by the modified Ashworth scale. In addition, a decrease of the number of spontaneous EMG events which probably indicate spasms was observed. Increase in bladder capacity at leakpoint following 4 weeks of frequent ejaculation with PVS treatment was likewise demonstrated.

CONCLUSION

PVS has proved its importance for SCL male fertility, in the years to come its place in treatment of spasticity and neurogenic detrusor overactivity has to be established.

Pathophysiology of spastic paresis. II: Emergence of muscle overactivity

In the subacute and chronic stages of spastic paresis, stretch-sensitive (spastic) muscle overactivity emerges as a third fundamental mechanism of motor impairment, along with paresis and soft tissue contracture. Part II of this review primarily addresses the pathophysiology of the various forms of spastic overactivity. It is argued that muscle contracture is one of the factors that cause excessive responsiveness to stretch, which in turn aggravates contracture. Excessive responsiveness to stretch also impedes voluntary motor neuron recruitment, a concept termed stretch-sensitive paresis. None of the three mechanisms of impairment (paresis, contracture, and spastic overactivity) is symmetrically distributed between agonists and antagonists, which generates torque imbalance around joints and limb deformities. Thus, each may be best treated focally on an individual muscle-by-muscle basis. Intensive motor training of the less overactive muscles should disrupt the cycle of paresis-disuse-paresis, and concomitant use of aggressive stretch and focal weakening agents in their more overactive and shortened antagonists should break the cycle of overactivity-contracture-overactivity.

Reflex reciprocal facilitation of antagonist muscles in spinal cord injury

STUDY DESIGN

Electromyographic study in complete and incomplete spinal cord injury (SCI).

OBJECTIVE

To examine the changes in the pattern of reciprocal inhibition between agonist and antagonist muscles in SCI.

SETTINGS

Sensory Motor Performance Program, Rehabilitation Institute of Chicago, IL, USA.

METHODS

Tendon taps were delivered manually with an instrumented hammer to the tendons of the tibialis anterior and soleus muscle in positions of full-ankle dorsiflexion and plantarflexion in eight subjects with complete SCI and eight subjects with incomplete SCI. Electromyographic activity (EMG) was recorded from ankle dorsiflexor and plantarflexor muscles. Tapping force was also recorded by a force sensor mounted to the tendon hammer, indicating the stimulus onset. Measures of reflex EMG magnitude and reflex latency were obtained for both agonist and antagonist muscles. The ratio of antagonist to agonist EMG was computed based on normalized EMG.

RESULTS

Substantial reflex responses occurred in both the stretched muscle and in its antagonist. The reflex in antagonist, which we term 'reciprocal facilitation (RF)', was most evident in subjects with incomplete SCI. The magnitude of RF was consistently greater than reflex responses in agonist muscles under all test conditions. The latency of the RF was comparable to that of monosynaptic reflex response.

CONCLUSIONS

Following SCI, reciprocal organization of segmental reflexes at the ankle is often partially or completely suppressed, allowing reflex activation in antagonist muscles to be manifested. Possible mechanisms underlying these changes in neural organization are discussed.

SPONSORSHIP

This study was supported by Spinal Cord Research Foundation, the Paralyzed Veterans of America.

Excitability of Spinal Inhibitory Circuits in Patients with Spasticity

The excitability of Ia inhibition and D1 inhibition after stimulation of the common peroneal nerve to the soleus motoneuron pool was investigated in 37 spastic patients at rest and onset of voluntary ankle dorsiflexion. Ia inhibition was determined as the short-latency depression of the soleus H-reflex and D1 inhibition as the long-latency depression. There was no significant difference in Ia inhibition between the paraplegic and control groups, however Ia inhibition in the hemiplegic group was significantly decreased. D1 inhibition was reduced in the paraplegic and hemiplegic groups compared with controls. Although inhibition of the soleus H-reflex appeared at the onset of voluntary dorsiflexion in control subjects, it was not observed in the patients. Although the excitability of the Ia inhibitory pathway at rest in the patients did not differ from that in control subjects, facilitation of the Ia inhibitory pathway at the onset of movement was decreased in the patients. Ia inhibition and D1 inhibition were evaluated in two paraplegic patients who were treated with local anesthesia and surgery, respectively. The excitability of both inhibitory pathways at rest was unchanged despite improvement of reciprocal movement in one patient, and was enhanced despite reduction in muscle strength in the other patient. The excitability of spinal inhibitory pathways at rest was not always reflected by motor function in spastic patients.

Kinetic and kinematic workspaces of the index finger following stroke

The objective of this study was to explore motor impairment of the index finger following stroke. More specifically, the kinetics and kinematics of the index finger were analysed throughout its workspace. Twenty-four stroke survivors with chronic hemiparesis of the hand participated in the trials, along with six age-matched controls. Hand impairment was classified according to the clinical Chedoke-McMaster Stage of Hand scale. Subjects were instructed to generate fingertip force in six orthogonal directions at five different positions within the workspace. Split-plot analysis of variance revealed that clinical impairment level had a significant effect on measured force (P < 0.001), with the weakness in stroke survivors being directionally dependent (P < 0.01). Electromyographic recordings revealed altered muscle activation patterns in the more impaired subjects. Unlike the control subjects, these subjects exhibited peak muscle excitation of flexor digitorum superficialis, extensor digitorum communis and first dorsal interosseous during the generation of fingertip flexion forces. Subjects also attempted to reach locations scattered throughout the theoretical workspace of the index finger. Quantification of the active kinematic workspace demonstrated a relationship between impairment level and the percentage of the theoretical workspace that could be attained (P < 0.001). The stroke survivors exhibited a high correlation between mean force production and active workspace (R = 0.90). Thus, our data suggest that altered muscle activation patterns contribute to directionally dependent weakness following stroke. Both the modulation of muscle excitation with force direction and the independence of muscle activation seem to be reduced. These alterations translate into a significantly reduced active range of motion for the fingers.

Galvanic evoked vestibulospinal and vestibulocollic reflexes in stroke

OBJECTIVE

Following stroke, the startle reflex, mediated via the reticulospinal tract, is often facilitated. Vestibulospinal reflexes are another bulbospinal reflex, abnormalities of which may contribute to impaired body posture and stance following stroke. We recorded galvanic evoked vestibulospinal and vestibulocollic reflexes to assess whether these showed similar changes to those for startle following stroke affecting the pons and above.

METHODS

Twenty-four stroke subjects (aged 40-82) were studied in the vestibulospinal part of the study, 21 stroke subjects (aged 40-81 years) were studied in the vestibulocollic part, including 18 studied in both. Transmastoid galvanic (DC) current was used to stimulate the vestibular nerve. Vestibulocollic responses were recorded from the sternocleidomastoid muscles and vestibulospinal responses from over soleus in standing subjects.

RESULTS

Vestibulocollic reflex amplitudes and latencies showed no significant differences between the two sides. Similarly short latency (SL) and medium latency (ML) vestibulospinal reflexes did not differ significantly in frequency, latency or amplitude between the affected and unaffected legs.

CONCLUSIONS

Vestibular reflexes are not facilitated by stroke at or above the pontine level. The exaggeration of startle by stroke may be specific to this reflex.

Antispastic effect of penile vibration in men with spinal cord lesion11No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the author(s) or on any organization with which the author(s) is/are associated

OBJECTIVE

To evaluate the possible antispastic effect of penile vibratory stimulation (PVS) in men with spinal cord lesion (SCL).

DESIGN

Unblinded, before-after trial.

SETTING

Ambulatory care.

PARTICIPANTS

Nine men with SCLs from C2 to T8 were randomly allocated into 2 groups.

INTERVENTION

Twenty-four hours of electromyographic recordings from the quadriceps and tibialis anterior muscles were taken, followed by PVS or no treatment and another 24 hours of electromyographic recordings. The presence of electromyographic activity of an amplitude 4 times the baseline, with a duration of more than 5 seconds, was taken to signify a spasm. The number of spasms per hour was calculated before and after PVS and no treatment. Spasticity was evaluated by the Modified Ashworth Scale (MAS).

MAIN OUTCOME MEASURE

Reduction in spasticity and spasms.

RESULTS

The electromyographic data showed a significant reduction in the frequency of leg spasms up to 3 hours (P<.05). Significantly decreased spasticity, as evaluated by MAS, was found immediately after vibration (P<.01).

CONCLUSIONS

PVS may be useful as an antispastic therapy.

Biomechanic characteristics of patients with spastic and dystonic hypertonia in cerebral palsy11No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors(s) or upon any organization with which the author(s) is/are associated

OBJECTIVE

To determine what biomechanic characteristics of knee joint motion and walking show potential to quantitatively differentiate spasticity and dystonia in cerebral palsy (CP).

DESIGN

Descriptive measurement study.

SETTING

University hospital.

PARTICIPANTS

Seventeen pediatric and adult patients with CP.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

We measured the resistance of the knee joint at different velocities and positions, maximum muscle activation during external motion, amplitude of knee tendon reflexes, maximum isometric flexion and extension torques, velocity of walking, and knee kinematics during the gait cycle. Patients were classified into 2 groups (dystonia or spasticity) if at least 2 of 3 physicians agreed that a prominent component of dystonia was present.

RESULTS

Patients with dystonia had a greater degree of co-contraction and an increased resistance to external motion at slow velocities. The tendon reflexes were almost normal in patients with dystonia, whereas they were increased in patients with spasticity. Muscle strength was more impaired in patients with dystonia, probably as a result of greater muscle co-contraction. They also walked slower, with smaller knee ranges of motion, during the stance phase of walking.

CONCLUSIONS

The measurement of resistance and of muscle activation during passive motion and tendon reflexes shows potential to differentiate dystonia from spasticity in CP patients with a mixed form of hypertonia. More studies are needed to confirm these results.

Physiological effects of botulinum toxin in spasticity

There is considerable evidence that injection of botulinum toxin (BTX) into muscles with spastic overactivity reduces resistance to passive movement in joints supplied by the injected muscles. The demonstration of improvement in active performance of the paretic limbs has been only anecdotal to date, and represents the most difficult challenge in research on BTX therapy in spastic paralysis. Data are reviewed that indicate several neurophysiological actions of BTX, other than the blocking of acetylcholine release at the neuromuscular ending: effects on the central nervous system, including retrograde axonal transport, reduced motoneuronal excitability, action on central synapses such as decreased Renshaw inhibition and increased presynaptic inhibition; action on gamma motoneuronal endings; action on most active terminals; spread of BTX to neighboring muscles; spread of BTX effects to remote muscles. Several of these neurophysiological actions are likely to contribute to improvement in active movements, as they may antagonize the primary mechanisms of functional impairment in patients with spastic paralysis: weakness, spastic cocontraction, spastic dystonia, and muscle shortening. We review the evidence for reduction of spastic cocontraction in both the injected muscle and its antagonist, and for improvement of antagonist weakness after BTX injection. The capacity of intramuscular BTX to reduce spastic dystonia and lengthen shortened muscles is also discussed based on prior literature. When injected into the more overactive of a pair of spastic antagonists around a joint, BTX should affect all the main mechanisms impairing active function around the joint.

Shoulder muscle activity in Parkinson's disease during multijoint arm movements across a range of speeds

Bradykinesia is one of the primary symptoms of Parkinson disease and leads to significant functional limitations for patients. Single joint movement studies, that have investigated the mechanism of bradykinesia, suggest that several features of muscle activity are disrupted, including modulation of burst amplitude and duration, and the number of bursts. It has been proposed that it is the blending of these different burst deficits that collectively defines bradykinesia. This study adds two new approaches to the study of bradykinesia. First, we examined the features of shoulder muscle activities during multijoint arm movement in bradykinetic and control subjects, such that previously reported single joint hypotheses could be tested for generalized arm movement. Second, we directly manipulated speed while keeping distance constant for a large range of speeds. In this manner, we could compare individual trials of muscle activity between controls and subjects with Parkinson's disease (PD) for movements matched for both speed and movement duration. Our results showed that while a multiple burst pattern of shoulder muscles was a common strategy for all subjects (young, elderly controls and PD), subjects with PD showed several burst abnormalities, including deficits in initial agonist burst amplitude and duration at both fast and slow speeds. Subjects with PD also (1) failed to produce a one-burst pattern at fast speeds and, instead, produced a predominance of multiple burst patterns and (2) showed a relationship between the number of burst deficits and the severity of disease. These results extend the findings of single joint studies to multi-joint and similarly indicate that a combination of burst modulation abnormalities correlate with bradykinesia and disease severity.

Quantitative evaluation of reflex and voluntary activity in children with spasticity

OBJECTIVE

To determine whether increased reflexes are related to functional impairment in children with spasticity.

DESIGN

Descriptive measurement study.

SETTING

Rehabilitation department in Poland.

PARTICIPANTS

Sixteen able-bodied children and 29 children with spasticity.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Measurement of modulation function of knee tendon reflexes by isometric knee extension, maximum isometric knee flexion, and extension torques, and scoring of ambulation in patients.

RESULTS

In able-bodied children, the reflex modulation function increased with voluntary knee extension, reached maximum at 5% to 20% of voluntary extension, and then decreased. The reflex modulation function in patients fell into 2 major categories. In the majority of affected limbs, the modulation function was inverse, with maximum reflex response at relaxation, and decreased with an increase of voluntary extension. In the remaining limbs, the shape of the reflex modulation function was normal, although other parameters changed. Isometric torques decreased more in flexion (65%) than in extension (39%). A torque decrease was a result of cocontraction more often during knee flexion (65%) than in knee extension (24%). The larger the reflexes, the more flexion torque decreased and ambulation deteriorated. This pattern occurred in patients with inverse modulation function but not in those with normal modulation function. The reciprocal inhibition from knee flexors to extensors could be affected in patients with inverse modulation function and cocontraction during flexion, whereas other mechanisms occurred in other patients.

CONCLUSIONS

The experimental design has potential as a quantitative measure of abnormal control in children with spasticity and can lead to more precise treatment selection criteria.

Patterned sensory stimulation induces plasticity in reciprocal ia inhibition in humans

Training of spinal cord circuits using sensorimotor stimulation has been proposed as a strategy to improve movement after spinal injury. How sensory stimulation may lead to long-lasting changes is not well understood. We studied whether sensory stimulation might induce changes in the strength of a specific spinal interneuronal circuit: spinally mediated reciprocal Ia inhibition. In healthy humans, the strength of reciprocal inhibition between ankle flexor and extensor muscles was assessed before and after 30 min of peroneal nerve stimulation at motor threshold intensity. Three stimulation protocols were assessed: patterned nerve stimulation (10 pulses at 100 Hz every 1.5 sec), uniform nerve stimulation (one pulse every 150 msec), and combined stimulation of the peroneal nerve and the motor cortex with transcranial magnetic stimulation. Short-latency reciprocal inhibition from ankle flexor to extensor muscles was measured by conditioning the soleus H-reflex with stimulation of the common peroneal nerve. The strength of the reciprocal inhibition was measured at baseline and for 20 min after each stimulation session. Patterned stimulation, with or without motor cortex stimulation, enhanced reciprocal inhibition for at least 5 min afterward. The uniform pattern of stimulation was ineffective. These results demonstrate the presence of short-term plasticity within spinal inhibitory circuits. We conclude that the pattern of sensory input is a crucial factor for inducing changes in the spinal circuit for reciprocal inhibition in humans. These findings may have implications for the use of repetitive patterned sensory stimulation in rehabilitative efforts to improve walking ability in patients with spinal injury.

Modulatory effects of alpha1-,alpha2-, and beta -receptor agonists on feline spinal interneurons with monosynaptic input from group I muscle afferents

Previous studies have shown that monoamines may modulate operation of spinal neuronal networks by depressing or facilitating responses of the involved neurons. Recently, activation of interneurons mediating reciprocal inhibition from muscle spindle (Ia) afferents and nonreciprocal inhibition from muscle spindle and tendon organ (Ia/Ib) afferents in the cat was found to be facilitated by noradrenaline (NA). However, which subclass membrane receptors are involved in mediating this facilitation was not established; the aim of the present experiments was to investigate this. Individual Ia- and Ia/Ib-inhibitory interneurons were identified in the cat lumbar spinal cord, and NA agonists were applied close to these neurons by ionophoresis. The agonists included the alpha1-receptor agonist phenylephrine, the alpha2-receptor agonists clonidine and tizanidine, and the beta-receptor agonist isoproterenol. Effects were measured by comparing changes in the number of extracellularly recorded spike potentials evoked by electrical stimulation of muscle nerves and changes in the latency of these potentials before, during, and after application of the tested compounds. Results show that the facilitatory effect of phenylephrine is as strong as that of NA, whereas the facilitatory effect of isoproterenol is weaker. Clonidine depressed activity of both Ia- and Ia/Ib-inhibitory interneurons, whereas tizanidine had no effect. These findings lead to the conclusion that beneficial antispastic effects of clonidine and tizanidine in humans are unlikely to be associated with an enhancement of the actions of Ia- and Ia/Ib-inhibitory interneurons, and the findings also support previous proposals that these compounds exert their antispastic actions via effects on other neuronal populations.

Spinal interneurones; how can studies in animals contribute to the understanding of spinal interneuronal systems in man?

The first part of this review deals with arguments that the essential properties and organization of spinal interneuronal systems in the cat and in man are similar. The second part is concerned with the possibility that some interneuronal systems may be responsible for motor disturbances caused by spinal cord injuries and that these interneurones may be defined. This possibility is discussed with respect to the hyperexcitability of alpha-motoneurones and the exaggeration of stretch reflexes in spastic patients. To this end, what is known about cat spinal interneurones and about the neuronal basis and pharmacological treatment of spasticity, is put together. Interneurones in di- and trisynaptic reflex pathways from group II muscle afferents are singled out, since they are depressed by the alpha(2) noradrenaline receptor agonists clonidine and tizanidine, which is a critical feature of interneurones expected to contribute to exaggerated stretch reflexes which are reduced by alpha(2) noradrenaline receptor agonists. Recent observations that reflex excitation of extensor motoneurones from group II afferents is enhanced in spastic patients and that the pathologically strong reflex actions of group II afferents are reduced by clonidine and tizanidine support this proposal. On the other hand, a lack of effect of clonidine and tizanidine upon other types of excitatory or inhibitory interneurones argues against any major contribution of such interneurones to the abnormally strong responses of alpha-motoneurones to muscle stretch.

Reciprocal Ia inhibition in patients with asymmetric spinal spasticity

OBJECTIVES

Previous studies on reciprocal Ia inhibition in spinal spasticity were contradictory, probably due to differences in the etiology, severity, and the course of recovery from the disease. The purpose of the present study was to establish a correlation between Ia inhibition and clinical abnormalities in spasticity following a spinal cord injury (SCI).

METHODS

We studied reciprocal Ia inhibition in bilateral soleus muscles in five SCI patients with marked asymmetry of spasticity and functional recovery for the right and left legs. Reciprocal Ia inhibition was determined from the short latency suppression of the soleus H-reflex by conditioning stimulation of the peroneal nerve.

RESULTS

In all the patients, Ia inhibition was asymmetric. Ia inhibition in the legs with good recovery and less spasticity was pronounced, but Ia inhibition in the more spastic legs was small or absent. Facilitation was seen only on the sides with poor recovery in two patients. In the healthy subjects the amount of Ia inhibition varied, but no side-to-side difference was found.

CONCLUSIONS

These results suggest that reciprocal Ia inhibition varies according to the functional recovery. Pronounced Ia inhibition may be related to good functional recovery in patients with SCI.

Combined use of body weight support, functional electric stimulation, and treadmill training to improve walking ability in individuals with chronic incomplete spinal cord injury

OBJECTIVE

To assess the effect of an intervention combining body weight support (BWS), functional electric stimulation (FES), and treadmill training on overground walking speed (OGWS), treadmill walking speed, speed and distance, and lower extremity motor scores (LEMS).

DESIGN

Before and after comparison.

SETTING

Miami Project to Cure Paralysis.

PARTICIPANTS

Nineteen subjects with American Spinal Injury Association class C injury who were at least 1 year postinjury and had asymmetrical lower extremity function.

INTERVENTION

Subjects trained 1.5 hours per day, 3 days per week, for 3 months. The training consisted of body weight-supported treadmill walking assisted by electric stimulation. Stimulation was applied to common peroneal nerve of the weaker lower extremity (LE) and timed to assist with the swing phase of the step cycle.

MAIN OUTCOME MEASURES

OGWS in the absence of both BWS and FES; LEMS, and treadmill training parameters of speed and distance.

RESULTS

Over the course of training, there was a significant increase in OGWS (from.12 +/- 0.8m/s to .21 +/- .15m/s, p = .0008), treadmill walking speed (from .23 +/- .12m/s to.49 +/- .20m/s, p = .00003), and treadmill walking distance (from 93 +/- 84m to 243 +/- 139m, p = .000001). The median LEMS increased significantly for both the stimulated and nonstimulated leg (from 8 to 11 in the FES-assisted leg, from 15 to 18 in the nonassisted leg, p < .005 for each).

CONCLUSIONS

All subjects showed improvement in OGWS and overall LE strength. Further research is required to delineate the essential elements of these particular training strategies.

Impairment of voluntary control of finger motion following stroke: role of inappropriate muscle coactivation

Subjects with chronic hemiplegia following stroke attempted to perform voluntary isometric, isokinetic, and free contractions of the extensor muscles of the metacarpophalangeal (MCP) joints. We recorded torque, metacarpophalangeal joint angle and velocity, and electromyographic (EMG) activity of the extrinsic extensors and flexors and the first dorsal interosseous (FDI). We found that voluntary MCP joint extension in hemiparetic subjects was greatly impaired in comparison with control subjects: only two of the 11 stroke subjects were able to generate even 0.21 N-m of isometric extension torque, only two could produce positive finger extension with no load, and none could develop an isokinetic concentric extension. Deficits seemed to result from a combination of coactivation of the finger flexor and extensor muscles and decreased voluntary excitation of the extensors, as normalized flexor and FDI EMG activity were greater for stroke than for control subjects (P < 0.001), but normalized extensor activity was reduced (P < 0.001).

Relation between abnormal patterns of muscle activation and response to common peroneal nerve stimulation in hemiplegia

OBJECTIVE

To investigate the relation between response to common peroneal nerve stimulation, timed to the swing phase of walking, and abnormal ankle movement and muscle activation patterns.

METHOD

Eighteen patients who took part had a drop foot and had had a stroke at least 6 months before the study Twelve age matched normal subjects were also studied. Response to stimulation was measured by changes in the speed and effort of walking when the stimulator was used. Speed was measured over 10 m and effort by the physiological cost index. Abnormal ankle movement and muscle activation were measured in a rig by ability to follow a tracking signal moving sinusoidally at either 1 or 2 Hz, resistance to passive movement, and EMG activity during both passive and active movements. Indices were derived to define EMG response to passive stretch, coactivation, and ability to activate muscles appropriately during active movement

RESULTS

Different mechanisms underlying the drop foot were seen. Results showed that patients who had poor control of ankle movement and spasticity, demonstrated by stretch reflex and coactivation, were more likely to respond well to stimulation. Those with mechanical resistance to passive movement and with normal muscle activation responded less well.

CONCLUSIONS

The results support the hypothesis that stimulation of the common peroneal nerve to elicit a contraction of the anterior tibial muscles also inhibits the antagonist calf muscles. The technique used may be useful in directing physiotherapy by indicating the underlying cause of the drop foot.

The effect of baclofen on the transmission in spinal pathways in spastic multiple sclerosis patients

OBJECTIVES

To measure the effect of baclofen on the transmission in different spinal pathways to soleus motoneurones in spastic multiple sclerosis patients.

METHODS

Baclofen was administered orally in 14 and intrathecally in 8 patients. H(max)/M(max), presynaptic inhibition by biceps femoris tendon tap of femoral nerve stimulation, depression of the soleus H-reflex following previous activation of the Ia afferents from the soleus muscle (i.e. postactivation depression), disynaptic reciprocal Ia inhibition of the soleus H-reflex and the number of backpropagating action potentials in primary afferents, which may be a sign of presynaptic inhibition, were examined.

RESULTS

Baclofen depressed the soleus H(max)/M(max) ratio significantly following oral and intrathecal baclofen. None of the two tests of presynaptic inhibition, or the postactivation depression or the disynaptic reciprocal Ia inhibition of the soleus H-reflex were affected by baclofen administration. Also the action potentials of the primary afferents were unchanged during baclofen administration.

CONCLUSIONS

The antispastic effect of baclofen is not caused by an effect on the transmitter release from Ia afferents or on disynaptic reciprocal Ia inhibition. One possible explanation of the depression of the H-reflex by baclofen is suggested to be a direct depression of motoneuronal excitability.

Inhibition of the triceps surae stretch reflex by stimulation of the deep peroneal nerve in persons with spastic stroke

OBJECTIVE

To reduce the triceps surae stretch reflex by electrical stimulation of the deep peroneal nerve.

DESIGN

Intervention study.

SETTING

Research institution.

PARTICIPANTS

Sample of convenience of 10 spastic stroke individuals.

INTERVENTION

After the deep peroneal nerve was stimulated between 0.9 and 4 times tibialis anterior motor threshold, the triceps surae was stretched to elicit a reflex.

MAIN OUTCOME MEASURE

The triceps surae stretch reflex was quantified by the amplitude of the reflex electromyography (EMG) in soleus and medial gastrocnemius muscles and mean ankle moment. Paired t test and the Wilcoxon signed rank test (p < .05) were used to evaluate the effect of conditioning stimulation.

RESULTS

The soleus stretch reflex EMG was reduced significantly (p < .001) by stimulating the deep peroneal nerve to 25%+/-6% (standard error) of the unconditioned value (relaxed triceps surae). The optimal interval between stimulation and stretch was 141+/-15 msec. The velocity threshold increased significantly (p = .006) from a median value of 8 degrees per second to 33 degrees per second and the area under the stretch velocity/stretch reflex relation decreased significantly (p < .001) (soleus EMG).

CONCLUSIONS

The stretch reflex of relaxed triceps surae in persons with spastic stroke can be extensively reduced by stimulating the deep peroneal nerve at several times motor threshold of the tibialis anterior.

Gait abnormalities in minimally impaired multiple sclerosis patients

Subclinical evidence of gait abnormalities were identified in a group of seven patients with multiple sclerosis, EDSS scored 0 - 2, without functional limitations. A movement analysis technique was used to identify gait parameters indicative of impaired motor function during walking. Abnormalities related primarily to time-distance parameters (reduced speed of progression, shorter strides, prolonged double support phase) and muscular function (premature recruitment of gastrocnemius and late relaxation of tibialis anterior during stance phase) were identified regardless the severity of the clinical score. The gait analysis procedure was able to provide the clinician with evidence of motor abnormalities prior to functional disturbance observable by a trained physician. These minimal dysfunctions may have resulted from reflex mechanisms impaired by delayed transmission through long loop pathways or else as a result of a nonspecific protective gait strategy to improve balance control. The technique described in this study may be useful to identify earlier starting points for follow-up and physiotherapy.

What functions do reflexes serve during human locomotion?

Studies on the reflex modulation of vertebrate locomotion have been conducted in many different laboratories and with many different preparations: for example, lamprey swimming, bird flight, quadrupedal walking in cats and bipedal walking in humans. Emerging concepts are that reflexes are task-, phase- and context-dependent. To function usefully in a behaviour such as locomotion wherein initial conditions change from step to step, reflexes would have to show modulation. Papers are reviewed in which the study of different reflexes have been conducted during different behaviours, with an emphasis on experiments in humans. A framework is developed in which the modulation and flexibility of reflexes are demonstrated. Alterations in cutaneous, and muscle (stretch and load receptor) reflexes between sitting, standing and walking are discussed. Studies in which both electrical, mechanical and 'natural' receptor activation have been conducted during walking are reviewed. Reflexes are shown to have important regulatory functions during human locomotion. A framework for discussion of reflex function throughout the step cycle is developed. The function of a given reflex pathway changes dynamically throughout the locomotor cycle. While all reflexes act in concert to a certain extent, generally cutaneous reflexes act to alter swing limb trajectory to avoid stumbling and falling. Stretch reflexes act to stabilize limb trajectory and assist force production during stance. Load receptor reflexes are shown to have an effect on both stance phase body weight support and step cycle timing. After neurotrauma or in disease, reflexes no longer function as during normal locomotion, but still have the potential to be clinically exploited in gait modification regimens.

Impaired modulation of quadriceps tendon jerk reflex during spastic gait: differences between spinal and cerebral lesions

In healthy subjects, functionally appropriate modulation of short latency leg muscle reflexes occurs during gait. This modulation has been ascribed, in part, to changes in presynaptic inhibition of Ia afferents. The changes in modulation of quadriceps tendon jerk reflexes during gait of healthy subjects were compared with those of hemi- or paraparetic spastic patients. The spasticity was due to unilateral cerebral infarction or traumatic spinal cord injury, respectively. The modulation of the quadriceps femoris tendon jerk reflex at 16 phases of the step cycle was studied. The reflex responses obtained during treadmill walking were compared with control values obtained during gait-mimicking standing postures with corresponding levels of voluntary muscle contraction and knee angles. In healthy subjects the size of the reflexes was profoundly modulated and was generally depressed throughout the step cycle. In patients with spinal lesion the reflex depression during gait was almost removed and was associated with weak or no modulation during the step cycle. In patients with cerebral lesion there was less depression of the reflex size associated with a reduced reflex modulation on the affected side compared with healthy subjects. On the 'unaffected' side of these patients reflex modulation was similar to that of healthy subjects, but the reflex size during gait was not significantly different from standing control values. These observations suggest that the mechanisms responsible for the depression of reflex size and the modulation normally seen during gait in healthy subjects are impaired to different extents in spasticity of spinal or cerebral origin, possibly due to the unilateral preservation of fibre tracts in hemiparesis.

Walking after spinal cord injury: evaluation, treatment, and functional recovery

OBJECTIVE

To present some recent developments and concepts emerging from both animal and human studies aimed at enhancing recovery of walking after spinal cord injury (SCI).

DATA SOURCES

Researchers in the field of restoration of walking after SCI, as well as references extracted from searches in the Medline computerized database.

STUDY SELECTION

Studies that reported outcome measures of walking for spinal cord injured persons with an incomplete motor function loss or cats with either a complete or incomplete spinal section.

DATA EXTRACTION

Data were extracted and validity was assessed by the authors.

DATA SYNTHESIS

This review shows that a multitude of interventions--mechanical, electrical, or pharmacologic--can increase the walking abilities of persons with SCI who have incomplete motor function loss.

CONCLUSIONS

A comprehensive evaluation of walking behavior requires tasks involving the different control variables. This comprehensive evaluation can be used to characterize the process of recovery of walking as well as the effectiveness of various treatments.

H-reflex modulations during voluntary and automatic movements following upper motor neuron damage

OBJECTIVES

It is not known whether similar mechanisms account for the impairments of voluntary movement and automatic postural responses of individuals with spasticity secondary to damage to the sensorimotor cortex and its projections (i.e. upper motor neuron syndrome (UMN)).

METHODS

The present study examined changes in soleus H-reflexes preceding and during voluntary tibialis anterior (TA) muscle contraction of standing subjects and during balance platform induced postural perturbations that elicited similar TA muscle contractions. Twenty-two subjects (12 non-disabled; 4 with spastic-type cerebral palsy; 6 with adult-onset cerebral vascular accident) participated in the study. Data were analyzed using ANOVAs and Tukey HSD post-hoc comparison tests to assess the timing and magnitude of soleus H-reflex amplitude changes relative to the onset of TA muscle activation.

RESULTS

Results indicated that, regardless of the level of TA activation, soleus H-reflexes of subjects with UMN involvement did not demonstrate inhibition either. during voluntary movements or during automatic postural perturbations.

CONCLUSIONS

These findings indicate that postural reflexes, as well as volitional movements, are impaired following UMN damage and that deficits in neural pathways subserving reciprocal inhibition contribute to the impairments.

Long-lasting depression of soleus motoneurons excitability following repetitive magnetic stimuli of the spinal cord in multiple sclerosis patients

The effect of repetitive magnetic stimulation at the spinal level on the soleus H-reflex amplitude was evaluated in II MS patients with lower limb spasticity and in nine healthy subjects. In MS patients stimulation with a train of 16 stimuli at 25 Hz induced a decrease in amplitude to 61.2 +/- 25.7% of the unconditioned H-reflex amplitude at interstimulus interval (ISI) of 10-1000 ms (P < 0.01). The amount of decrease in H-reflex amplitude was highly dependent on the stimulation intensity and the placement of the coil, and to a lesser extent influenced by the stimulation frequency. No decrease in motor evoked potentials (MEPs) evoked by transcranial magnetic stimulation was seen following trains of 16 stimuli at mid-thoracic in contrast to the post-stimulation depression in H-reflex amplitude which could imply that mechanisms acting at presynaptic level were involved. In response to repetitive magnetic stimuli for 5 min, a long-lasting decrease in H-reflex amplitude to a level of about 70% of the pre-stimulation H-reflex amplitude occurred in MS patients (P < 0.01). A similar although not significant decrease was observed in healthy subjects. We propose that long-lasting depression of the soleus H-reflex amplitude after repetitive magnetic stimuli is due to long-term depression of the synaptic transmission.

Evident difference in the excitability of the motoneuron pool between normal subjects and patients with spasticity assessed by a new method using H-reflex and M-response

The excitability of the motoneuron (MN) pool in the resting state was compared between normal control subjects and patients with spasticity resulting from HTLV-I-associated myelopathy, using a new parameter, Hslp/Mslp, and the conventional parameters Hmax/Mmax and Hth/Mth. Differences in the excitability of the MN pool between these two groups reached a high degree of statistical significance only when assessed with the new parameter. This suggests the methodological advantage of the Hslp/Mslp over both Hmax/Mmax and Hth/Mth for evaluation of the excitability of the MN pool in the resting state.

Central control of disynaptic reciprocal inhibition in humans

The disynaptic pathway from muscle spindle Ia afferents to motoneurones of the antagonist muscle is one of the best studied pathways in the spinal cord. Early animal studies--mainly in the cat--have provided a detailed knowledge of the pathway itself and of the integration of segmental and supraspinal convergence at the interneuronal level. Although this knowledge was used to formulate hypotheses on the function of the pathway during natural movements, the reduced animal preparation limited the possibilities of testing these ideas. However, such information has more recently been obtained from human subjects by using indirect electrophysiological techniques. In most of these experiments the disynaptic Ia inhibition was demonstrated as a short-latency depression of a monosynaptic test reflex (H-reflex) following a conditioning stimulation of the antagonist nerve. Changes in the size of this depression during voluntary tasks were then taken as evidence of a central regulation of the pathway. It has for example been demonstrated in this way that the brain regulates the Ia inhibitory interneurones in parallel with their corresponding motoneurones during extension-flexion movements, but not during co-contraction of antagonistic muscles. The importance of the central control of the pathway has also been emphasized by the finding of a disordered regulation of its activity in patients with lesions of the brain. This may possibly contribute to the inappropriate co-contraction of antagonistic muscles observed in some of these patients. It seems reasonable to expect that this kind of experiment in the future may contribute significantly to the knowledge of the central control of spinal motor mechanisms.