Regional cerebral blood flow changes in human brain related to ipsilateral and contralateral complex hand movements--a PET study

Ipsilateral deficits in 1-handed shoe tying after left or right hemisphere stroke

Poole JL, Sadek J, Haaland KY. Ipsilateral deficits in 1-handed shoe tying after left or right hemisphere stroke.

OBJECTIVE

To examine 1-handed shoe tying performance and whether cognitive deficits more associated with left or right hemisphere damage differentially affect it after unilateral stroke.

DESIGN

Observational cohort comparing ipsilesional shoe tying, spatial and language skills, and limb praxis.

SETTING

Primary care Veterans Affairs and private medical center.

INTERVENTIONS

Not applicable.

PARTICIPANTS

Volunteer right-handed sample of adults with left or right hemisphere damage and healthy demographically matched adults.

MAIN OUTCOME MEASURE

The number of correct trials and the total time to complete 10 trials tying a shoe using the 1-handed method.

RESULTS

Both stroke groups had fewer correct trials and were significantly slower tying the shoe than the control group. Spatial skills predicted accuracy and speed after right hemisphere damage. After left hemisphere damage, accuracy was predicted by spatial skills and limb praxis, while speed was predicted by limb praxis only.

CONCLUSIONS

Ipsilesional shoe tying is similarly impaired after left or right hemisphere damage, but for different reasons. Spatial deficits had a greater influence after right hemisphere damage, and limb apraxia had a greater influence after left hemisphere damage. Language deficits did not affect performance, indicating that aphasia does not preclude using this therapy approach. These results suggest that rehabilitation professionals should consider assessment of limb apraxia and ipsilesional skill training in the performance of everyday tasks.

Motor imagery influences the execution of repetitive finger opposition movements

Motor imagery (MI) is the ability to imagine performing a movement without executing it. In literature, there have been numerous reports on the influence of MI on motor practice and the beneficial effects of "mental practice" on the physical performance has been suggested to rely to the close temporal association between motor rehearsal and actual performance. In the present study, we aimed to evaluate whether the addition of a period of motor imagery between two motor practice trials could modify movement execution in a repetitive finger opposition motor task performed at maximal speed and whether the effect of motor imagery on motor practice is dependant on the complexity of movement. We observed that the addition of motor imagery to the sole motor practice was able to influence the performance of repetitive finger opposition movements inducing an increase of the velocity of movement greater than that observed with the motor practice alone. Further the addition of motor imagery was able to induce a modification in the motor strategy in terms of duration of the main phases of movements. This was more evident when subjects executed a finger sequential task with respect to a simple finger tapping task. We assume that mental rehearsal facilitates the brain network involved in sensorimotor control, particularly acting on those neural structures involved in the motor program.

Functional asymmetry in the cerebellum: a brief review

Recent discoveries on the way in which the cerebellum carries out higher non-motor functions, have stimulated a proliferation of researches into functional integration and neural mechanisms in the cerebellum. Cerebellar functional asymmetry is a special characteristic of cerebellar functional organization and the cerebro-cerebellar circuitry that underlies task performance. Multi-level neuroimaging studies demonstrate that cerebellar functional asymmetry has a rather complex pattern, and may be correlated with practice or certain disorders. In this review, we summarize some new and important advances in the understanding of functional laterality of the cerebellum in primary motor and higher cognitive functions, and highlight the differences in the patterns of cerebellar functional asymmetry in the various functional domains. We propose that cerebellar functional asymmetry may be associated with the pattern of connectivity between a large number of widely distributed brain areas and between special cerebellar functional regions. It is suggested that cerebro-cerebellar circuits in particular play an important role in cerebellar functional asymmetry. Finally, we propose that multi-scale connectivity analyses and careful studies of high-level cerebellar functional asymmetry would make an important contribution to the understanding of the human cerebellum and cerebral neural networks.

Cortical control of unilateral simple movement in healthy aging

Normal aging is associated with several modifications in the cerebral motor system that reflect into an increased and more bilateral activation in elderly subjects. Twelve young and nine elderly healthy right-handed subjects performed a self-initiated brisk right thumb extension while recorded with 32-channel EEG. The aging effect over cortical generators of bereithshaftspotential, reconstructed using cortical current density (CCD) method and a realistic volume conductor, was evaluated in five different periods and in both mesial and lateral motor-related areas. Over-activation occurred mainly at movement initiation in those areas related to simple movements (caudal mesial areas and both sensorimotor cortices) and in contralateral sensorimotor cortex during the post-movement phase. In those areas, the elderly group recruited a larger neuronal population than the young one in the presence of a significantly longer movement. This more likely suggests their reduced selectivity in activating the motor cortex than a compensatory mechanism to produce an optimum performance. Movement duration resulted negatively correlated with pre-SMA activity, suggesting its involvement in movement termination.

Leg preference and interlateral performance asymmetry in soccer player children

Strength of leg preference and interlateral asymmetry in kinematics of kicking a ball for power were assessed in 6- to 10-year-old right-footed soccer player children. Leg preference was evaluated separately for three task categories: balance stabilization, soccer related mobilization, and general mobilization. The results showed that while both categories of mobilization tasks were featured by a consistent preference for the right leg, in stabilization tasks we observed lower scores and greater interindividual variability of leg preference. No effect of age was detected on leg preference. Analysis of peak foot velocity revealed similar increment of performance of the right and left legs from the ages 6-8 to 10 years. This finding supports the notion of stable magnitude of interlateral asymmetries of performance during motor development.

Gaze and hand position effects on finger-movement-related human brain activation

Humans commonly use their hands to move and to interact with their environment by processing visual and proprioceptive information to determine the location of a goal-object and the initial hand position. It remains elusive, however, how the human brain fully uses this sensory information to generate accurate movements. In monkeys, it appears that frontal and parietal areas use and combine gaze and hand signals to generate movements, whereas in humans, prior work has separately assessed how the brain uses these two signals. Here we investigated whether and how the human brain integrates gaze orientation and hand position during simple visually triggered finger tapping. We hypothesized that parietal, frontal, and subcortical regions involved in movement production would also exhibit modulation of movement-related activation as a function of gaze and hand positions. We used functional MRI to measure brain activation while healthy young adults performed a visually cued finger movement and fixed gaze at each of three locations and held the arm in two different configurations. We found several areas that exhibited activation related to a mixture of these hand and gaze positions; these included the sensory-motor cortex, supramarginal gyrus, superior parietal lobule, superior frontal gyrus, anterior cingulate, and left cerebellum. We also found regions within the left insula, left cuneus, left midcingulate gyrus, left putamen, and right tempo-occipital junction with activation driven only by gaze orientation. Finally, clusters with hand position effects were found in the cerebellum bilaterally. Our results indicate that these areas integrate at least two signals to perform visual-motor actions and that these could be used to subserve sensory-motor transformations.

Unique cortical physiology associated with ipsilateral hand movements and neuroprosthetic implications

BACKGROUND AND PURPOSE

Brain computer interfaces (BCIs) offer little direct benefit to patients with hemispheric stroke because current platforms rely on signals derived from the contralateral motor cortex (the same region injured by the stroke). For BCIs to assist hemiparetic patients, the implant must use unaffected cortex ipsilateral to the affected limb. This requires the identification of distinct electrophysiological features from the motor cortex associated with ipsilateral hand movements.

METHODS

In this study we studied 6 patients undergoing temporary placement of intracranial electrode arrays. Electrocorticographic (ECoG) signals were recorded while the subjects engaged in specific ipsilateral or contralateral hand motor tasks. Spectral changes were identified with regards to frequency, location, and timing.

RESULTS

Ipsilateral hand movements were associated with electrophysiological changes that occur in lower frequency spectra, at distinct anatomic locations, and earlier than changes associated with contralateral hand movements. In a subset of 3 patients, features specific to ipsilateral and contralateral hand movements were used to control a cursor on a screen in real time. In ipsilateral derived control this was optimal with lower frequency spectra.

CONCLUSIONS

There are distinctive cortical electrophysiological features associated with ipsilateral movements which can be used for device control. These findings have implications for patients with hemispheric stroke because they offer a potential methodology for which a single hemisphere can be used to enhance the function of a stroke induced hemiparesis.

A regulation role of the prefrontal cortex in the fist-edge-palm task: evidence from functional connectivity analysis

The Fist-Edge-Palm (FEP) task is a motor sequencing task that is widely used in neurological examination. Deficits in this task are believed to reflect impairment in the frontal lobe regions. However, two recent functional brain imaging studies of the FEP task using conventional subtraction analysis failed to demonstrate FEP-induced activation in the prefrontal cortex (PFC), which contradicts existing neuropsychological literature. In this study, psychophysiological interaction (PPI) analysis was used to reanalyze our previous neuroimaging dataset from 10 healthy subjects in order to evaluate the changes of functional connectivity between the sensorimotor cortex and the prefrontal regions during the performances of the FEP task relative to simple motor control tasks. The PPI analysis revealed significantly increased functional connectivity between bilateral sensorimotor cortex and the right inferior and middle frontal cortex during the performance of the FEP task compared with the control tasks. However, regional signal changes showed no significant activation differences in these prefrontal regions. These results provide evidence supporting the involvement of the frontal lobe in the performance of the FEP task, and suggest a role of regulation, rather than direct participation, of the prefrontal cortex in the execution of complex motor sequence tasks such as the FEP task.

Gaze influences finger movement-related and visual-related activation across the human brain

The brain uses gaze orientation to organize myriad spatial tasks including hand movements. However, the neural correlates of gaze signals and their interaction with brain systems for arm movement control remain unresolved. Many studies have shown that gaze orientation modifies neuronal spike discharge in monkeys and activation in humans related to reaching and finger movements in parietal and frontal areas. To continue earlier studies that addressed interaction of horizontal gaze and hand movements in humans (Baker et al. 1999), we assessed how horizontal and vertical gaze deviations modified finger-related activation, hypothesizing that areas throughout the brain would exhibit movement-related activation that depended on gaze angle. The results indicated finger movement-related activation related to combinations of horizontal, vertical, and diagonal gaze deviations. We extended our prior findings to observation of these gaze-dependent effects in visual cortex, parietal cortex, motor, supplementary motor area, putamen, and cerebellum. Most significantly, we found a modulation bias for increased activation toward rightward, upper-right and vertically upward gaze deviations. Our results indicate that gaze modulation of finger movement-related regions in the human brain is spatially organized and could subserve sensorimotor transformations.

1-Hz repetitive TMS over ipsilateral motor cortex influences the performance of sequential finger movements of different complexity

To elucidate the role of ipsilateral motor cortex (M1) in the control of unilateral finger movements (UFMs) in humans we used a conditioning protocol of 1-Hz repetitive transcranial magnetic stimulation (1-Hz rTMS) over M1 in 11 right-handed healthy subjects. We analysed the effects of conditioning rTMS on UFMs of different complexity (simple vs sequential finger movements), and performed with a different modality (internally vs externally paced movements). UFMs were monitored with a sensor-engineered glove, and a quantitative evaluation of the following parameters was performed: touch duration (TD); inter-tapping interval (ITI); timing error (TE); and number of errors (NE). 1-Hz rTMS over ipsilateral M1 was able to affect the performance of a sequence of finger opposition movements in a metronome-paced condition, significantly increasing TD and reducing ITI without TE changes. The effects on motor behaviour had a different magnitude as a function of the sequence complexity. Further, we found a different effect of the ipsilateral 1-Hz rTMS on externally paced movements with respect to an internally paced condition. All these findings indicate that ipsilateral M1 plays an important role in the execution of sequential UFMs. Interestingly, NE did not change in any experimental condition, suggesting that ipsilateral M1 influences only the temporal and not the spatial accuracy of UFMs. Finally, the duration (up to 30 min) of 1-Hz rTMS effects on ipsilateral M1 can indicate its direct action on the mechanisms of cortical plasticity, suggesting that rTMS can be used to modulate the communication between the two hemispheres in rehabilitative protocols.

Bilateral representation in the deep cerebellar nuclei

The cerebellum is normally assumed to represent ipsilateral movements. We tested this by making microelectrode penetrations into the deep cerebellar nuclei (mainly nucleus interpositus) of monkeys trained to perform a reach and grasp task with either hand. Following weak single electrical stimuli, many sites produced clear bilateral facilitation of multiple forelimb muscles. The short onset latencies, which were similar for each side, suggested that at least some of the muscle responses were mediated by descending tracts originating in the brainstem, rather than via the cerebral cortex. Additionally, cerebellar neurones modulated their discharge with both ipsilateral and contralateral movements. This was so, even when we carefully excluded contralateral trials with evidence of electromyogram modulation on the ipsilateral side. We conclude that the deep cerebellar nuclei have a bilateral movement representation, and relatively direct, powerful access to limb muscles on both sides of the body. This places the cerebellum in an ideal position to coordinate bilateral movements.

Transcranial cortex stimulation and fMRI: electrophysiological correlates of dual-pulse BOLD signal modulation

Are the local hemodynamic changes in BOLD-fMRI correlated to increased or decreased neuronal activity or both? We combined transcranial electrical cortex stimulation (TES) with simultaneous fMRI and electromyographic (EMG) recording to study the influence of inhibitory and excitatory neuronal activity on the concomitant BOLD signal change. Unilateral or bilateral TES was applied with a postero-anterior orientation. This activates pyramidal cells transsynaptically and allows for the induction of cortical inhibition and excitation of the pyramidal cell, respectively. In this project interhemispheric inhibition (IHI) served as an in vivo model to investigate electrophysiologically well defined inhibitory and excitatory effects.

METHODOLOGY

Included event-related fMRI, which triggered TES; online recording of the EMG response monitored the inhibitory and excitatory influences on discharging corticospinal neurons.

RESULTS

Revealed that a single suprathreshold stimulus induced a positive BOLD response both in the ipsilateral as well as in the contralateral primary motor cortex (M1). The contralateral co-activation of the homotopic M1 should be a functional correlate of transcallosal connections. If a contralateral conditioning stimulus preceded the test stimulus by 10 ms (IHI), the subsequent ipsilateral BOLD signal was significantly reduced. We find that cortical inhibitory processes are accompanied by attenuation of the local neurovascular signal.

Shift of manual preference in right-handers following unimanual practice

The effect of unimanual practice of the non-preferred hand on manual asymmetry and manual preference for sequential finger movements was evaluated in right-handers before, immediately after, and 30 days following practice. The results demonstrate that unimanual practice induced a persistent shift of manual preference for the experimental task in most participants, but no significant correlation between manual asymmetry and manual preference was detected. These findings are explained by proposing that manual preference is influenced by a task-specific confidence developed from the recent history of differential use of the limbs, in interaction with a generalized confidence on a single hand for performance of motor skills.

Different contributions of the corpus callosum and cerebellum to motor coordination in monkey

We investigated the different contribution of the corpus callosum (CC) and cerebellum to motor control in two macaque monkeys trained to perform a precision grip task with one or both hands. Recordings were made from antidromically identified CC cells and nearby unidentified neurons (UIDs) in the hand representation of the supplementary motor area (SMA) and compared with cells from the deep cerebellar nuclei (DCN). All cells showed their greatest modulation in activity (rate change locked to particular task event) during the movement epochs of the task (CC, 21.3 +/- 22.2; UIDs, 36.2 +/- 30.1 spike/s for contralateral trials; DCN, 63 +/- 56.4 for ipsilateral trials; mean +/- SD). Surprisingly, CC cells fired at very low basal rates compared with UIDs (3.9 +/- 4.9 vs. 10 +/- 9.1 spike/s) or DCN neurons (50.8 +/- 23.8 spike/s). However, SMA cells had the greatest rate modulation to baseline ratio (CC: 12.1 +/- 13.7; UID: 5.3 +/- 5.4; DCN: 1.7 +/- 2.0). This would allow them to code the timing of a behavioral event with better fidelity than DCN cells. A multivariate regression analysis between cell firing and EMG measured cells' representation of moment-by-moment modulations in muscle activity. CC neurons coded these real-time behavioral parameters significantly less well than the other cells types, using both linear and nonlinear models. Basal firing rate substantially constrains cell function. CC cells with low basal rates have restricted dynamic range for coding continuous parameters, but efficiently code the time of discrete behavioral events. DCN neurons with higher basal rates are better suited to control continuously variable parameters of movement.

Ipsilesional motor deficits following stroke reflect hemispheric specializations for movement control

Recent reports of functional impairment in the 'unaffected' limb of stroke patients have suggested that these deficits vary with the side of lesion. This not only supports the idea that the ipsilateral hemisphere contributes to arm movements, but also implies that such contributions are lateralized. We have previously suggested that the left and right hemispheres are specialized for controlling different features of movement. In reaching movements, the non-dominant arm appears better adapted for achieving accurate final positions and the dominant arm for specifying initial trajectory features, such as movement direction and peak acceleration. The purpose of this study was to determine whether different features of control could characterize ipsilesional motor deficits following stroke. Healthy control subjects and patients with either left- or right-hemisphere damage performed targeted single-joint elbow movements of different amplitudes in their ipsilateral hemispace. We predicted that left-hemisphere damage would produce deficits in specification of initial trajectory features, while right-hemisphere damage would produce deficits in final position accuracy. Consistent with our predictions, patients with left, but not right, hemisphere damage showed reduced modulation of acceleration amplitude. However, patients with right, but not left, hemisphere damage showed significantly larger errors in final position, which corresponded to reduced modulation of acceleration duration. Neither patient group differed from controls in terms of movement speed. Instead, the mechanisms by which speed was specified, through modulation of acceleration amplitude and modulation of acceleration duration, appeared to be differentially affected by left- and right-hemisphere damage. These findings support the idea that each hemisphere contributes differentially to the control of initial trajectory and final position, and that ipsilesional deficits following stroke reflect this lateralization in control.

Hyperbaric oxygen and cerebral physiology

Hyperbaric oxygen (HBO) therapy is defined by the Undersea and Hyperbaric Medical Society (UHMS) as a treatment in which a patient intermittingly breathes 100% oxygen under a pressure that is greater than the pressure at sea level [a pressure greater than 1 atmosphere absolute (ATA)]. HBO has been shown to be a potent means to increase the oxygen content of blood and has been advocated for the treatment of various ailments, including air embolism, carbon monoxide poisoning, wound healing and ischemic stroke. However, definitive established mechanisms of action are still lacking. This has led to uncertainty among clinicians, who have understandingly become hesitant in regard to using HBO therapy, even in situations where it could prove beneficial. Therefore, this review will summarize the literature regarding the effects of HBO on brain oxygenation, cerebral blood flow and intracranial pressure in both the healthy and injured brains, as well as discuss how changes in these three factors can impart protection.

Effects of intermanual transfer induced by repetitive precision grip on input–output properties of untrained contralateral limb muscles

Although there were many reports relating to intermanual transfer of behavioral motor tasks in humans, it is still not well-known whether the transfer phenomenon between the trained and untrained hand is accompanied by corresponding changes in motor system. In the present study we applied transcranial magnetic stimulation to investigate the practice effects of unilateral fingertip precision grip on corticospinal excitability, regarding both the trained and untrained hand muscles. The results showed that after practice fingertip grip force became steady and safety margin dramatically decreased not only in the trained hand, but also in the untrained hand. Regarding MEP and background EMG (B.EMG) activities, the regression slope of MEP/B.EMG ratio in the first dorsal interosseous (FDI) muscle became significantly steeper after practice in both hands, but in the thenar (TH) muscle there were no clear modulations. These results indicated that through practice qualitative or functional changes of corticospinal systems related to the reorganization for a fingertip precision grip prominently reflect only on FDI muscle which plays a dominant role in the task. More importantly, such effects were simultaneously seen in the untrained hand correspondent to the trained hand, i.e., changes of input-output property in M1 occur not only in the trained hand, but also in the untrained hand. Based on the present results, we suggest that training-induced neural adaptations of the central nervous system may include improvement of its predicting fingertip grip force for self-lifting of the object in the untrained hand.

Global activation of primary motor cortex during voluntary movements in man

Unilateral voluntary movements are accompanied by robust activation of contralateral primary motor cortex (M1) in a somatotopic fashion. Occasionally, coactivation of M1 (M1-CoA) ipsilateral to the movement was described. In a study with brain tumor patients, we consistently observed additional somatotopic M1-CoAs and hypothesized that they might represent a basic feature of movement execution. To test this hypothesis, we used BOLD functional magnetic resonance imaging in healthy subjects and show that unilateral voluntary movements of the fingers or toes go along not only with contralateral M1 activation, but also with ipsilateral M1-CoA of the respective homotopic representation and bilateral M1-CoA of different heterotopic representations not directly involved in the executed movement. Moreover, bilateral M1-CoA of heterotopic representations was observed in tongue movements. All M1-CoAs respected the correct somatotopy; however, their Euclidean coordinates were shifted and resembled to those obtained for imagined movements rather than for actual movements. BOLD signal intensities and correlations to the applied hemodynamic reference function were lower in M1-CoAs as compared to the M1 activations driving the movement but did not differ between homo- and heterotopic M1-CoAs. Thus, we propose that specific unilateral voluntary movements are accompanied by a global activation of primary motor areas, reflecting an overall increase in neuronal activity and unraveling the fundamental principle of distributed processing in M1. Executive motor function may rely on a balance of inhibitory and excitatory neuronal activity, where actual movement would result from a shift towards excitation.

Interlimb transfer of visuomotor rotations depends on handedness

We previously reported that opposite arm adaptation to visuomotor rotations improved the initial direction of right arm movements in right-handers, whereas it only improved the final position accuracy of their left arm movements. We now investigate the pattern of interlimb transfer following adaptation to 30 degrees visuomotor rotations in left-handers to determine whether the direction of transfer depends on handedness. Our results indicate unambiguous transfer across the arms. In terms of final position accuracy, the direction of transfer is opposite to that observed in right-handers, such that transfer only occurred from the left to the right arm movements. Directional accuracy also showed the opposite pattern of transfer to that of right-handers: initial movement direction, calculated at peak tangential acceleration, transferred only from right to left arms. When movement direction was measured later in the movement, at peak tangential velocity, asymmetrical transfer also occurred, such that greater transfer occurred from right to left arms. However, a small, but significant influence of opposite arm adaptation also occurred for the left arm, which might reflect differences in the use of the nondominant arm between left- and right-handers. Overall, our results indicate that left-handers show a mirror-imaged pattern of interlimb transfer in visuomotor adaptation to that previously reported for right-handers. This pattern of transfer is consistent with the hypothesis that asymmetry in interlimb transfer is dependent on differential specialization of the dominant and nondominant hemisphere/limb systems for trajectory and positional control, respectively.

Increased cognitive load during simple and complex motor tasks in acute stage after stroke

The aim of this study was to assess the activation of primary motor cortex, prefrontal cortex and parietal cortex during simple and complex motor tasks performed with the hemiparetic and non-hemiparetic hand.

METHODS

Seven patients after stroke in the left brain hemisphere were included in the study. Functional magnetic resonance imaging (fMRI) was performed in the first and third week, and in three patients also three months after the stroke.

RESULTS

Performance of both the simple and the complex tasks with the hemiparetic or non-hemiparetic hand resulted in activations of the motor cortex, prefrontal cortex and parietal cortex in majority of the consecutive fMRI sessions. Three months after the stroke fMRI data revealed reduced activation of primary motor cortex and parietal cortex in the contralesional hemisphere during the performance of the simple task by the hemiparetic hand. During the complex task, the reduction of activation was less prominent.

CONCLUSIONS

Results of the present study suggest that in mildly impaired stroke patients a bilateral activation of prefrontal and parietal cortex may participate in the recovery process from stroke. The potential for measurement of cortical rehabilitation is discussed.

Extensive training of elementary finger tapping movements changes the pattern of motor cortex excitability

There is evidence of a strong capacity for functional and structural reorganization in the human motor system. However, past research has focused mainly on complex movement sequences over rather short training durations. In this study we investigated changes in corticospinal excitability associated with longer training of elementary, maximum-speed tapping movements. All participating subjects were consistent right-handers and were trained using either the right (experiment 1) or the left thumb (experiment 2). Transcranial magnetic stimulation was applied to obtain motor evoked potentials (MEPs) from the abductor pollicis brevis (APB) muscle of the right and the left hand before and after training. As a result of training, a significant increase was observed in tapping speed accompanied by increased MEPs, recorded from the trained APB muscle, following contralateral M1 stimulation. In the case of subdominant-hand training we additionally demonstrate increased MEP amplitudes evoked at the right APB (untrained hand) in the first training week. Enhanced corticospinal excitability associated with practice of elementary movements may constitute a necessary precursor for inducing plastic changes within the motor system. The involvement of the ipsilateral left M1 likely reflects the predominant role of the left M1 in the general control (modification) of simple motor parameters in right-handed subjects.

Complex Motor Function in Humans: Validating and Extending the Postulates of Alexandr R. Luria

OBJECTIVE

We used functional brain imaging to reevaluate Luria's postulates and to elaborate the neural circuitry underlying performance of complex motor tasks.

BACKGROUND

The anatomic organization and physiologic functioning of the normal human motor system have great significance for understanding motor dysfunction and remediation in neurology. Working with victims of penetrating head injuries, noted Russian neuropsychologist Aleksandr R. Luria designed several tests of fine motor control to understand their difficulties with complex voluntary movements. This led to his postulates that such function involves the premotor cortices and their interaction with the parietal lobe.

METHOD

Six healthy young adults performed the hand imitation, fist-scissors-gun, and piano key tasks during blood oxygen level-dependent functional magnetic resonance imaging at 3 T.

RESULTS

All 3 tasks revealed activation of both premotor and parietal cortices. Furthermore, while hand Imitation relied more on the ventral premotor area and right parietal lobe, fist-scissors-gun and piano key relied more on the supplementary motor cortex.

CONCLUSIONS

We postulate that differences in task-dependent activations across these tasks relate to degrees of sequential movement, pacing, and imitation. These results uphold Luria's original hypotheses, and extend that work by providing a further characterization of the motor areas involved in complex motor behaviors.

Prism adaptation in schizophrenia

The prism adaptation test examines procedural learning (PL) in which performance facilitation occurs with practice on tasks without the need for conscious awareness. Dynamic interactions between frontostriatal cortices, basal ganglia, and the cerebellum have been shown to play key roles in PL. Disruptions within these neural networks have also been implicated in schizophrenia, and such disruptions may manifest as impairment in prism adaptation test performance in schizophrenia patients. This study examined prism adaptation in a sample of patients diagnosed with schizophrenia (N=91) and healthy normal controls (N=58). Quantitative indices of performance during prism adaptation conditions with and without visual feedback were studied. Schizophrenia patients were significantly more impaired in adapting to prism distortion and demonstrated poorer quality of PL. Patients did not differ from healthy controls on aftereffects when the prisms were removed, but they had significantly greater difficulties in reorientation. Deficits in prism adaptation among schizophrenia patients may be due to abnormalities in motor programming arising from the disruptions within the neural networks that subserve PL.

The neural basis of motor sequencing: an fMRI study of healthy subjects

The present study used functional MRI to clarify the brain regions activated during a series of motor sequencing tasks in healthy volunteers. Ten subjects were scanned while performing three soft signs tasks ranging from simple (PT: palm tapping), moderate (PS: pronation/supination) to complex movements (FEP: fist-edge-palm). The FEP task induced significant activations within the cortical networks including bilateral sensorimotor, SMA, left parietal, and right cerebellum, but no activation in the prefrontal area. Moreover, the percentage signal changes within the left sensorimotor, left thalamus and right cerebellum showed an increase in activation with task complexity. The present findings challenge the traditional belief that FEP was a task for frontal lobe function but suggest that successful performance of more complex neurological soft sign tasks like FEP requires the participation of more brain areas than simple motor sequencing and coordination task like PS and PT. These also provide the empirical data on the neural basis of neurological soft signs for further study in other clinical group like schizophrenia in the near future.

Interregional long-range and short-range synchrony: a basis for complex sensorimotor processing

Communication of distant brain areas provides the basis for integration of complex information in order to adapt to changes in the environment, to process this information, and to generate appropriate behavioral responses necessary for successful behavior in daily life. How is interregional communication realized in the brain? Perceptions and actions are likely to be represented in the brain by large numbers of distributed neurons firing in synchrony. This synchronous activity of distributed neuronal networks can be noninvasively evaluated by multichannel surface electroencephalography (EEG) and the event-related analysis of synchronous EEG signals in the frequency domain. In this chapter we will discuss the role of interregional synchronous activity and its relevance as a mechanism for implementation of successful human complex behavior exemplified within studies of complex finger movements, context-dependent control of complex motor behavior, bimanual motor tasks, visuo-tactile integration, and recovery of motor functions after stroke. These studies provide evidence that synchronous interregional neuronal activity, determined by event-related synchronization (ERS) and desynchronization (ERD), task-related power increases (TRPI) and decreases (TRPD), and event- and task-related coherence (ERCoh, TRCoh) analysis, is one important mechanism for cortical implementation of successful human complex behavior and adaptation to changes in daily life. These results are discussed in the light of recent findings in animal models, substantiating the view of the relevance of interregional synchronous activity for information coding and control of behavior.

Reduction of the hand representation in the ipsilateral primary motor cortex following unilateral section of the corticospinal tract at cervical level in monkeys

BACKGROUND

After sub-total hemi-section of cervical cord at level C7/C8 in monkeys, the ipsilesional hand exhibited a paralysis for a couple of weeks, followed by incomplete recovery of manual dexterity, reaching a plateau after 40-50 days. Recently, we demonstrated that the level of the plateau was related to the size of the lesion and that progressive plastic changes of the motor map in the contralesional motor cortex, particularly the hand representation, took place following a comparable time course. The goal of the present study was to assess, in three macaque monkeys, whether the hand representation in the ipsilesional primary motor cortex (M1) was also affected by the cervical hemi-section.

RESULTS

Unexpectedly, based on the minor contribution of the ipsilesional hemisphere to the transected corticospinal (CS) tract, a considerable reduction of the hand representation was also observed in the ipsilesional M1. Mapping control experiments ruled out the possibility that changes of motor maps are due to variability of the intracortical microstimulation mapping technique. The extent of the size reduction of the hand area was nearly as large as in the contralesional hemisphere in two of the three monkeys. In the third monkey, it represented a reduction by a factor of half the change observed in the contralesional hemisphere. Although the hand representation was modified in the ipsilesional hemisphere, such changes were not correlated with a contribution of this hemisphere to the incomplete recovery of the manual dexterity for the hand affected by the lesion, as demonstrated by reversible inactivation experiments (in contrast to the contralesional hemisphere). Moreover, despite the size reduction of M1 hand area in the ipsilesional hemisphere, no deficit of manual dexterity for the hand opposite to the cervical hemi-section was detected.

CONCLUSION

After cervical hemi-section, the ipsilesional motor cortex exhibited substantial reduction of the hand representation, whose extent did not match the small number of axotomized CS neurons. We hypothesized that the paradoxical reduction of hand representation in the ipsilesional hemisphere is secondary to the changes taking place in the contralesional hemisphere, possibly corresponding to postural adjustments and/or re-establishing a balance between the two hemispheres.

Grasping with the left and right hand: a kinematic study

The goal of the present study was to compare prehension movements of the dominant and the non-dominant hand. Twenty right-handed volunteers (age 20-30 years) reached forward to grasp a cylindrical object, which was lifted and then placed into a target position in a retraction-insertion movement. The movements were performed at three different velocities (normal, deliberately fast, or slowly) both, under visual control, and in a no-vision condition. Analysis of the kinematic data revealed that the speed of hand transport influenced pre-shaping of both hands in a similar way. In the visual condition, the grip aperture increased about linearly with peak transport velocity, while it increased non-linearly with shorter movement duration. Comparison of the regression parameters showed that these relationships were nearly identical for both hands. The dominant hand was faster in inserting the object into the target position. Otherwise, no significant inter-manual differences were found. During prehension without visual control, the fingers opened more and movement duration was prolonged. Except for a larger grip aperture of the dominant hand at the end of the acceleration phase, the kinematic data of both hands were again comparable. This invariance was in contrast to performance in fine motor skills such as a pegboard test and drawing movements, where there was a clear advantage of the dominant hand. The similar pre-shaping of both hands during prehension is discussed with regard to a common motor representation of grasping.

Gating of SEPs by contraction of the contralateral homologous muscle during the preparatory period of self-initiated plantar flexion

To investigate the centrifugal change in somatosensory information processing caused by contraction of the contralateral homologous muscle, we recorded the somatosensory-evoked potentials (SEPs) during the preparatory period of a self-initiated plantar flexion. The SEPs following stimulation of the right tibial nerve at the popliteal fossa were recorded in nine healthy subjects. Self-initiated plantar flexion of the left ankle was performed once every 5 to 7 s. The electrical stimulation was delivered continuously, and the subjects were instructed to concentrate on the movement and not to pay attention to the electrical stimulation. Based on the components of movement-related cortical potential, Bereitschaftspotential (BP) and Negative slope (NS), the preparatory period was divided into four sub-periods (NS, BP-1, BP-2, and Pre-BP). To obtain pre-movement SEPs, the signals following stimulation in each sub-period were averaged. SEPs were attenuated in the preparatory period, especially in the NS sub-period. The amplitude of N40 component was significantly attenuated compared with that in the stationary state and other sub-periods. The amplitude of P53 and N70 was smaller in the NS sub-period than other pre-movement sub-periods. Since there was no centripetal effect on SEPs in the preparatory period, these findings suggested that the activity of motor-related areas modulated the somatosensory information from the contralateral non-movement limb (centrifugal gating). It was assumed that an inhibition on the somatosensory inputs from contralateral limb was caused by the projection via either the corpus callosum or ipsilateral cortico-cortical projections.

Role of the cerebellum in implicit motor skill learning: a PET study

To depict neural substrates of implicit motor learning, regional cerebral blood flow was measured using positron emission tomography (PET) in 13 volunteers in the rest condition and during performance of a unimanual two-ball rotation task. Subjects rotated two balls in a single hand; a slow rotation (0.5 Hz) was followed by two sessions requiring as rapid rotation as possible. The process was repeated four times by a single hand (Block 1) and then by the opposite hand (Block 2). One group of volunteers began with the right hand (n = 7), and the other with the left (n = 6). Performance was assessed by both quickness and efficiency of movements. The former was assessed with the maximum number of rotation per unit time, and the latter with the electromyographic activity under constant speed of the movement. Both showed learning transfer from the right hand to the left hand. Activation of cerebrum and cerebellum varied according to hand. Activation common to both hands occurred in the bilateral dorsal premotor cortex and parasagittal cerebellum, right inferior frontal gyms, left lateral cerebellum and thalamus, supplementary motor area, and cerebellar vermis. The left lateral cerebellum showed the most prominent activation on the first trial of the novel task, and hence may be related the early phase of learning, or "what to do" learning. Left parasagittal cerebellum activity diminished with training both in first and second blocks, correlating inversely with task performance. This region may therefore be involved in later learning or "how to do" learning. The activity of these regions was less prominent with prior training than without it. Thus the left cerebellar hemisphere may be related to learning transfer across hands.

Temporal dynamics of ipsilateral and contralateral motor activity during voluntary finger movement

The role of motor activity ipsilateral to movement remains a matter of debate, due in part to discrepancies among studies in the localization of this activity, when observed, and uncertainty about its time course. The present study used magnetoencephalography (MEG) to investigate the spatial localization and temporal dynamics of contralateral and ipsilateral motor activity during the preparation of unilateral finger movements. Eight right-handed normal subjects carried out self-paced finger-lifting movements with either their dominant or nondominant hand during MEG recordings. The Multi-Start Spatial Temporal multi-dipole method was used to analyze MEG responses recorded during the movement preparation and early execution stage (-800 msec to +30 msec) of movement. Three sources were localized consistently, including a source in the contralateral primary motor area (M1) and in the supplementary motor area (SMA). A third source ipsilateral to movement was located significantly anterior, inferior, and lateral to M1, in the premotor area (PMA) (Brodmann area [BA] 6). Peak latency of the SMA and the ipsilateral PMA sources significantly preceded the peak latency of the contralateral M1 source by 60 msec and 52 msec, respectively. Peak dipole strengths of both the SMA and ipsilateral PMA sources were significantly weaker than was the contralateral M1 source, but did not differ from each other. Altogether, the results indicated that the ipsilateral motor activity was associated with premotor function, rather than activity in M1. The time courses of activation in SMA and ipsilateral PMA were consistent with their purported roles in planning movements.

Sensing limb movements in the motor cortex: how humans sense limb movement

We can precisely control only what we can sense. Sensing limb position or limb movement is essential when we precisely control our limb movements. It has been generally believed that somatic perception takes place in the neuronal network of somatosensory areas. Recent neuroimaging techniques (PET, fMRI, transcranial magnetic stimulation) have revealed in human brains that motor areas participate in somatic perception of limb movements during kinesthetic illusion in the absence of actual limb movement. In particular, the primary motor cortex, which is an executive locus of voluntary limb movements, is primarily responsible for kinesthetic perception of limb movements. This probably forms the most efficient circuits for voluntary limb movements between the controlled muscles and the motor areas.

Cerebral perturbations provoked by prolonged exercise

This review addresses cerebral metabolic and neurohumoral alterations during prolonged exercise in humans with special focus on associations with fatigue. Global energy turnover in the brain is unaltered by the transition from rest to moderately intense exercise, apparently because exercise-induced activation of some brain regions including cortical motor areas is compensated for by reduced activity in other regions of the brain. However, strenuous exercise is associated with cerebral metabolic and neurohumoral alterations that may relate to central fatigue. Fatigue should be acknowledged as a complex phenomenon influenced by both peripheral and central factors. However, failure to drive the motorneurons adequately as a consequence of neurophysiological alterations seems to play a dominant role under some circumstances. During exercise with hyperthermia excessive accumulation of heat in the brain due to impeded heat removal by the cerebral circulation may elevate the brain temperature to >40 degrees C and impair the ability to sustain maximal motor activation. Also, when prolonged exercise results in hypoglycaemia, perceived exertion increases at the same time as the cerebral glucose uptake becomes low, and centrally mediated fatigue appears to arise as the cerebral energy turnover becomes restricted by the availability of substrates for the brain. Changes in serotonergic activity, inhibitory feed-back from the exercising muscles, elevated ammonia levels, and alterations in regional dopaminergic activity may also contribute to the impaired voluntary activation of the motorneurons after prolonged and strenuous exercise. Furthermore, central fatigue may involve depletion of cerebral glycogen stores, as signified by the observation that following exhaustive exercise the cerebral glucose uptake increases out of proportion to that of oxygen. In summary, prolonged exercise may induce homeostatic disturbances within the central nervous system (CNS) that subsequently attenuates motor activation. Therefore, strenuous exercise is a challenge not only to the cardiorespiratory and locomotive systems but also to the brain.

Hemodynamic evoked response of the sensorimotor cortex measured noninvasively with near-infrared optical imaging

We have performed a noninvasive bilateral optical imaging study of the hemodynamic evoked response to unilateral finger opposition task, finger tactile, and electrical median nerve stimulation in the human sensorimotor cortex. This optical study shows the hemoglobin-evoked response to voluntary and nonvoluntary stimuli. We performed measurements on 10 healthy volunteers using block paradigms for motor, sensory, and electrical stimulations of the right and left hands separately. We analyzed the spatial/temporal features and the amplitude of the optical signal induced by cerebral activation during these three paradigms. We consistently found an increase (decrease) in the cerebral concentration of oxy-hemoglobin (deoxy-hemoglobin) at the cortical side contralateral to the stimulated side. We observed an optical response to activation that was larger in size and amplitude during voluntary motor task compared to the other two stimulations. The ipsilateral response was consistently smaller than the contralateral response, and even reversed (i.e., a decrease in oxy-hemoglobin, and an increase in deoxy-hemoglobin) in the case of the electrical stimulation. We observed a systemic contribution to the optical signal from the increase in the heart rate increase during stimulation, and we made a first attempt to subtract it from the evoked hemoglobin signal. Our findings based on optical imaging are in agreement with results in the literature obtained with positron emission tomography and functional magnetic resonance imaging.

Event-related desynchronization and excitability of the ipsilateral motor cortex during simple self-paced finger movements

OBJECTIVE

To study the time course of oscillatory EEG activity and corticospinal excitability of the ipsilateral primary motor cortex (iM1) during self-paced phasic extension movements of fingers II-V.

METHODS

We designed an experiment in which cortical activation, measured by spectral-power analysis of 28-channel EEG, and cortical excitability, measured by transcranial magnetic stimulation (TMS), were assessed during phasic self-paced extensions of the right fingers II-V in 28 right-handed subjects. TMS was delivered to iM1 0-1500 ms after movement onset.

RESULTS

Ipsilateral event-related desynchronization (ERD) during finger movement was paralleled by increased cortical excitability of iM1 from 0-200 ms after movement onset and by increased intracortical facilitation (ICF) without changes in intracortical inhibition (ICI) or peripheral measures (F waves). TMS during periods of post-movement event-related synchronization (ERS) revealed no significant changes in cortical excitability in iM1.

CONCLUSIONS

Our findings indicate that motor cortical ERD ipsilateral to the movement is associated with increased corticospinal excitability, while ERS is coupled with its removal. These data are compatible with the concept that iM1 contributes actively to motor control. No evidence for inhibitory modulation of iM1 was detected in association with self-paced phasic finger movements.

SIGNIFICANCE

Understanding the physiological role of iM1 in motor control.

Asymmetric regional cerebral blood flow in sedated baboons measured by positron emission tomography (PET)

The analysis of structural brain asymmetry has been a focal point in anthropological theories of human brain evolution and the development of lateralized behaviors. While physiological brain asymmetries have been documented for humans and animals presenting with pathological conditions or under certain activation tasks, published studies on baseline asymmetries in healthy individuals have produced conflicting results. We tested for the presence of cerebral blood flow asymmetries in 7 healthy, sedated baboons using positron emission tomography, a method of in vivo autoradiography. Five of the 7 baboons exhibited hemispheric asymmetries in which left-sided flow was significantly greater than right-sided flow. Furthermore, the degree of asymmetry in 8 of 24 brain regions was found to be significantly correlated with age; older individuals exhibited a higher degree of asymmetry than younger individuals. Cerebral blood flow itself was uncorrelated with age, and differences between males and females were not significant.

Power grip disinhibits the ipsilateral sensorimotor cortex: a TMS and fMRI study

Electrophysiological studies have shown that forceful activation of the hand muscles (power grip) is accompanied by an increased excitability of the ipsilateral corticospinal system. This increase in excitability may be due to spinal or cortical mechanisms. Here we show with fMRI that this phenomenon is at least in part mediated at a cortical level. We used TMS to show that the increased ipsilateral excitability during a forceful maneuver leads to enhanced stimulus-response curves. fMRI was used to compare the activation during a repetitive hand movement with or without an accompanying power grip on the opposite site. The power grip reduced movement-related activation in the ipsilateral sensorimotor cortex. Peak deactivation was located in the left postcentral gyrus extending into the adjacent precentral gyrus. This finding suggests that a forceful activation of the hand muscles disinhibits a distinct functional representation in the ipsilateral sensorimotor cortex. Consequently, the excitability of the corticospinal system increases and less neuronal excitatory activity is needed to perform a given task. The results may be important for a variety of studies as they suggest that fMRI may show decreased hemodynamic response under conditions in which other neurophysiological methods have shown increased functional activity.

Ipsilateral cortical activation during finger sequences of increasing complexity: representation of movement difficulty or memory load?

OBJECTIVE

To investigate, if increasing ipsilateral cortical activation during sequential finger movements of increasing complexity relates to the difficulty of transitions ('sequence complexity') or to increasing motor memory load ('sequence length').

METHODS

Pre-learned, memorized sequences (MEM) of different complexities (SIMPLE=e.g., 2-2-2-2-2-2-2-2-2-2-2-2-2-2-2-2; SCALE=e.g., 2-5-4-3-2-5-4-3-2-5-4-3-2-5-4-3; and COMPLEX=e.g., 5-3-2-4-3-4-2-5-4-4-2-3-5-2-4-3; 2=index, 5=pinky) were randomly alternated with visually instructed, novel sequences (NOV) of matched complexity. In this design, memory load co-varied with complexity during MEM because of increasing length of the memorized sequences. In NOV, memory load was eliminated because each sequence element was prompted by an instructive visual cue. Cortical activation was measured by spectral power analysis of 28-channel electroencephalogram (EEG) in 15 healthy, right-handed subjects.

RESULTS

The increases of ipsilateral sensorimotor activation from SIMPLE over SCALE to COMPLEX in NOV were linearly correlated with the corresponding pattern in MEM (P<0.01). No significant differences were found between MEM and NOV (analysis of variance, n.s.).

CONCLUSIONS

The similar dynamics of cortical activation patterns across movement sequences during MEM and NOV indicate that increasing ipsilateral activation primarily reflects processing of increasingly difficult transitions between movements, and not motor memory load.

SIGNIFICANCE

Function of ipsilateral sensorimotor areas during complex motor behavior.

Neural activity in primary motor and dorsal premotor cortex in reaching tasks with the contralateral versus ipsilateral arm

To investigate the effector dependence of task-related neural activity in dorsal premotor (PMd) and primary motor cortex (M1), directional tuning functions were compared between instructed-delay reaching tasks performed separately with either the contralateral or the ipsilateral limb. During presentation of the instructional cue, the majority (55/90, 61%) of cells in PMd were tuned with both arms, and their dynamic range showed a trend for stronger discharge with the contralateral arm. Most strikingly, however, the preferred direction of most of these latter cells (41/55, 75%) was not significantly different between arms. During movement, many PMd cells continued to be tuned with both arms (53/90, 59%), with a trend for increasing directional differences between the arms over the course of the trial. In contrast, during presentation of the instructional cue only 5/74 (7%) cells in M1 were tuned with both arms. During movement, about half of M1 cells (41/74, 55%) were tuned with both arms but the preferred directions of their tuning functions were often very different and there was a strong bias toward greater discharge rates when the contralateral arm was used. Similar trends were observed for EMG activity. In conclusion, M1 is strongly activated during movements of the contralateral arm, but activity during ipsilateral arm movements is also common and usually different from that seen with the contralateral arm. In contrast, a major component of task-related activity in PMd represents movement in a more abstract or task-dependent and effector-independent manner, especially during the instructed-delay period.

Aberrant Sensorimotor Integration in Musicians' Cramp Patients

AbstractSimple tapping and complex movements (Luria finger apposition task) were performed unimanually and bimanually by two groups of professional guitarists while EEG was recorded from electrodes over the sensorimotor cortex. One group had a task-specific movement disorder (focal dystonia or musicians' cramp), while the other group did not (controls). There were no significant group interactions in the task-related power (TRPow) within the alpha range of 8-10Hz (mu1). In contrast, there was a significant group interaction within the alpha range of 10-12Hz (mu2); these latter frequencies are associated with task-specific sensorimotor integration. The significant group interaction included task (simple and complex) by hand (left, right, and both) by electrodes (10 electrodes over the sensorimotor areas). In the rest conditions, the alpha power (10-12Hz) was comparable between the groups; during movement, however, compared to the controls, patients demonstrated the greatest TRPow (10-12Hz) over all conditions. This was particularly evident when patients used their affected hand and suggests that patients with musicians' cramp have impaired task-specific sensorimotor integration.

Ipsilesional deficits during fast diadochokinetic hand movements following unilateral brain damage

Impaired sensorimotor function of the hand ipsilateral to a unilateral brain lesion has been reported in a variety of motor tasks; however, elementary diadochokinetic movements, such as tapping with the index finger, seem to be preserved in chronic-lesion patients. Three different diadochokinetic movements (forearm diadochokinesis, hand tapping (HT) and finger tapping (FT)) were tested in patients with left brain damage (LBD) and right brain damage (RBD) and control subjects. Movements were measured three-dimensionally and the kinematics of joint angles were analyzed. While the patients' measures of movement speed and symmetry appeared normal, detailed kinematic analysis revealed clear deficits in several measures of movement variability, which reflected decreased regularity of the alternating movement cycles. This impairment was greater in LBD patients and tended to be greater during forearm diadochokinesis. The necessity of ipsilateral control in addition to dominant, contralateral control, especially during left hand and more complex or more proximal manual tasks may account for these findings. In addition, the role of apraxia (defined by impairments during the imitation of gestures) in the performance deficits of LBD patients was also assessed. Although, some performance decrements were associated with the presence of apraxia, these were different from the group findings and restricted to the two tapping tasks. Thus, although apraxia may have caused deficits in establishing dynamic representations of the elementary postures in conditions of high speed and low complexity, the disturbances during diadochokinetic movements must for the most part be attributed to more motor-related deficits of ipsilateral sensorimotor control, which are particularly apparent when the motor dominant left hemisphere is affected. The absence of clear correlations between performance deficits and lesion characteristics suggests that a distributed network is involved in this ipsilateral control.

Somatotopy in the ipsilateral primary motor cortex

Conflicting reports exist about the occurrence, reliability and localization of activation in the ipsilateral primary motor cortex (M1). We re-examined this issue with functional magnetic resonance imaging in 12 volunteers performing right hand, finger, wrist, elbow, foot and tongue movements in two separate sessions. Ipsilateral M1 activation was inconsistently and non-reliably present during all movements: in 54% of all hand, 50% elbow, 46% finger, 33% wrist, and in 17% of all foot experiments. When compared to contralateral M1, the volumes and maximum t-values were always smaller. The ipsilateral M1 body representation was somatotopically organized with coordinates similar to the contralateral M1. Finally, the presence of ipsilateral M1 activation depended on the global activation level in other motor-related areas, which was significantly increased, when ipsilateral M1 activation was detected.

Brain activation during the fist-edge-palm test: a functional MRI study

The purpose of our study is to clarify, using functional MRI, brain regions activated during the fist-edge-palm task (FEP) compared to relatively simple hand motor tasks using either the right or the left hand in right-handed normal volunteers. The FEP was introduced to detect a disorder of voluntary movement, and it is believed to be closely related to contralateral frontal lobe damage. However, this assumption still remains controversial. Ten subjects participated in this study. Hand motor tasks were as follows: (1) the FEP, in which the subjects were requested to place their hand in three different positions sequentially: a fist resting horizontally, a palm resting vertically, and a palm resting horizontally; (2) a fist-palm task (FP), in which the subjects were asked to clench and unclench their fist alternately; and (3) a control task requiring the subjects to knock lightly with their clenched fist. The contralateral sensomotor and premotor areas were activated in the FP with the right hand and the contralateral sensorimotor, premotor, and supplementary motor areas (SMA) were activated in the FP with the left hand. In the FEP with either hand, bilateral premotor and left parietal areas and ipsilateral cerebellum were also activated as well as contralateral sensorimotor area and SMA. Our results suggest that successful performance of the FEP requires the participation of more brain areas than FP, which may explain why some patients without frontal lobe damage failed to perform the FEP.

Bedside functional imaging of the premature infant brain during passive motor activation

BACKGROUND

Changes in regional brain blood flow and hemoglobin oxygen saturation occur in the human cortex in response to neural activation. Traditional functional radiologic methods cannot provide continuous, portable measurements. Imaging methods, which use near-infrared light allow for non-invasive measurements by taking advantage of the fact that hemoglobin is a strong absorber at these wavelengths.

AIMS

To test the feasibility of a new optical functional imaging system in premature infants, and to obtain preliminary brain imaging of passive motor activation in this population.

METHODS

A new optical imaging system, the Diffuse Optical Tomography System (DOTS), was used to provide real-time, bedside assessments. Custom-made soft flexible fiberoptic probes were placed on two extremely ill, mechanically ventilated 24 week premature infants, and three healthier 32 week premature infants. Passive motor stimulation protocols were used during imaging.

RESULTS

Specific movement of the arm resulted in reproducible focal, contralateral changes in cerebral absorption. The data suggest an overall increase in blood volume to the imaged area, as well as an increase in deoxyhemoglobin concentration. These findings in premature infants differ from those expected in adults.

CONCLUSIONS

In the intensive care setting, continuous non-invasive optical functional imaging could be critically important and, with further study, may provide a bedside monitoring tool for prospectively identifying patients at high risk for brain injury.

Different distribution of the activated areas in the dorsal premotor cortex during visual and auditory reaction-time tasks

Sensorimotor association is an essential aspect of behavior. The dorsal part of the premotor cortex (PMd) is known to have an important role in sensorimotor association. Although it is suggested that the partially segregated groups of neurons are involved in sensorimotor association in different sensory modalities, it is not yet clear whether these groups occupy the PMd to the same or different extent. Therefore, we performed a functional magnetic resonance imaging study to compare activated regions in the PMd during simple reaction-time tasks with visual and auditory cues. Eight normal volunteers performed two simple reaction time tasks with a conventional on-off design; one is with a visual cue and the other is with an auditory cue. In both tasks, two regions in the left primary motor area (M1) (4a and 4p) and the bilateral PMd were activated. The two activated regions in the left M1 occupied the same areas in both the visual and the auditory tasks. However, in the PMd, the activated regions were situate medially during the visual task and laterally during the auditory task, along the precentral sulci. There was no overlap of significantly activated regions between two tasks, and areas specifically activated during the visual task were observed in the middle of the precentral sulci, bilaterally. The results suggest that the distribution of PMd subregions involved in sensorimotor association differ when the sensory cues are in different modalities.

The role of the medial wall and its anatomical variations for bimanual antiphase and in-phase movements

The medial wall of the frontal cortex is thought to play an important role for bimanual coordination. However, there is uncertainty regarding the exact neuroanatomical regions involved. We compared the activation patterns related to bimanual movements using functional magnetic resonance imaging in 12 healthy right-handed subjects, paying special attention to the anatomical variability of the frontal medial wall. The subjects performed unimanual right and left and bimanual antiphase and in-phase flexion and extension movements of the index finger. Activation of the right supplementary motor area (SMA) proper, right and left caudal cingulate motor area (CMA), and right and left premotor cortices was significantly stronger during bimanual antiphase than bimanual in-phase movements, indicating an important function of these areas with bimanual coordination. A frequent anatomical variation is the presence of the paracingulate sulcus (PCS), which might be an anatomical landmark to determine the location of activated areas. Seven subjects had a bilateral, three a unilateral right, and two a unilateral left PCS. Because the area around the PCS is functionally closer coupled to the CMA than to the SMA, activation found in the area around the PCS should be attributed to the CMA. With anatomical variations such as the presence of a PCS or a vertical branch of the cingulate sulcus, normalization and determination of the activation with the help of stereotaxic coordinates can cause an incorrect shift of CMA activation to the SMA. This might explain some of the discrepancies found in previous studies.

Lateralization of motor circuits and handedness during finger movements

Although functional lateralization in the human brain has been studied intensively, there remains significant controversy over the brain mechanisms that instantiate it. The main objective of the present study is to characterize the regions associated with the generation of different movements by the fingers of both hands by right- and left-handed people. Thirteen right- and left-handers were studied using blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) during performance of single and sequential finger movement tasks. We used single-shot whole-brain spiral fMRI to map the functional components of the motor system during these tasks. Regions of interest included the primary motor and sensory cortices, the pre-motor cortices and the cerebellum. Sequential movements were associated with intense brain activation in several bilateral regions, whereas single movements were associated with less activation in fewer regions, but with greater laterality. Right- and left-handers differed in their pattern of activation, sharing a pattern of activation on simple movements but responding differently to sequential movements. On simple movements, the brain activation patterns of left- and right-handers were similar in volume, number of areas and laterality. By contrast, on sequential movement, left-handers activated larger volumes and a larger number of brain areas than right-handers, and showed significantly less brain lateralization. These results highlight differences in the functional organization of motor areas in right- and left-handed people. The discrepancies that might reflect differences in the network features of motor systems in these two groups, could also determine differences in motor activity that occur during recovery from injury (e.g. after stroke).