Distribution of slow cortical potentials preceding self-paced hand and hindlimb movements in the premotor and motor areas of monkeys

Surface negative-depth positive, slowly increasing potentials prior to self-paced hand and hindlimb movements were recorded in the dorsal aspect of the motor and premotor cortices with chronically implanted electrodes. It was shown that the potentials were recorded in the contralateral forelimb motor area prior to hand movements but were hardly seen in the hindlimb motor area. On hindlimb movements, the contralateral hindlimb motor area showed the premovement potentials, whereas the forelimb motor area revealed little or no premovement potentials. The contralateral premotor cortex was shown to induce the premovement potentials in its wider areas and participate in both of hand and hindlimb movements in a similar fashion, with predominances in its dorsolateral portion for hand movements and in its dorsomedial portion for hindlimb movements respectively. In the hemisphere ipsilateral to the moving hand, the relatively large premovement slow potentials emerged frequently also in the premotor cortex, whereas only the small potential was obtained from the forelimb motor area. These results suggest that the premotor cortex (area 6) participates in the more general and associative organization of motor function than the motor cortex (area 4) which represents the specialized role in the motor performance.     

Brain lateralization of motor imagery: motor planning asymmetry as a cause of movement lateralization

Movement asymmetry in humans and animals is often considered as being induced by the brain lateralization of the motor system. In the present work, the hemispheric asymmetry for motor planning as a cause of behavioral lateralization was examined. This study was carried out on normal volunteers and patients suffering unilateral brain damage caused by a stroke. Motor planning was evaluated by using the motor imagery of hand movement, a mental representation of a motor pattern that includes its internal simulation but not its real execution. The present study shows marked similarities between virtual movement executed during motor imagery and real movements. Thus, performance time showed a high correlation between real and virtual movements in the following conditions: (1) during dominant and non-dominant hand movements; (2) in simple and complex motor tasks; (3) in young control subjects; (4) in stroke patients; and (5) control subjects aged-matched to stroke patients. Brain strokes increased the performance time in both real and virtual movements. Left-brain strokes decreased the velocity of the real movements in both hands, whereas right-brain strokes mainly disturbed movements in the left hand. A similar effect was observed for virtual movements, suggesting a left-brain dominance for motor planning in humans. However, two-handed movement tasks suggest a complex interaction during motor planning, an interaction that facilitates motor performance during mirror movements and delays motor execution during non-mirror movements.     

Asymmetric spatiotemporal patterns of event-related desynchronization preceding voluntary sequential finger movements: a high-resolution EEG study.

OBJECTIVE: To study spatiotemporal patterns of event-related desynchronization (ERD) preceding voluntary sequential finger movements performed with dominant right hand and nondominant left hand. METHODS: Nine subjects performed self-paced movements consisting of three key strokes with either hand. Subjects randomized the laterality and timing of movements. Electroencephalogram (EEG) was recorded from 122 channels. Reference-free EEG power measurements in the beta band were calculated off-line. RESULTS: During motor preparation (-2 to -0.5s with respect to movement onset), contralateral preponderance of event-related desynchronization (ERD) (lateralized power) was only observed during right hand finger movements, whereas ERD during left hand finger movements was bilateral. CONCLUSIONS: For right-handers, activation on the left hemisphere during left hand movements is greater than that on the right hemisphere during right hand movements. SIGNIFICANCE: We provide further evidence for motor dominance of the left hemisphere in early period of motor preparation for complex sequential finger movements.     

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

The purpose of this study was to investigate the cortical motor areas activated in relation to unilateral complex hand movements of either hand, and the motor area related to motor skill learning. Regional cerebral blood flow (rCBF) was measured in eight right-handed healthy male volunteers using positron emission tomography during a two-ball-rotation task using the right hand, the same task using the left hand and two control tasks. In the two-ball-rotation tasks, subjects were required to rotate the same two iron balls either with the right or left hand. In the control task, they were required to hold two balls in each hand without movement. The primary motor area, premotor area and cerebellum were activated bilaterally with each unilateral hand movement. In contrast, the supplementary motor area proper was activated only by contralateral hand movements. In addition, we found a positive correlation between the rCBF to the premotor area and the degree of improvement in skill during motor task training. The results indicate that complex hand movements are organized bilaterally in the primary motor areas, premotor areas and cerebellum, that functional asymmetry in the motor cortices is not evident during complex finger movements, and that the premotor area may play an important role in motor skill learning.     

Effect of aging on sensorimotor functions of eye and hand movements

Changes in coordinated eye and hand movements with aging were studied in normal young and elderly subjects. Electrooculograms, flexor and extensor electromyograms, and potentials representing hand movements were recorded and used to evaluate the performance in aiming tasks. The parameters that reflect motor functions did not change significantly with aging in both eye and hand movements. However, elderly subjects commonly showed increases in reaction times of the initial (open-loop) movements in both eye and hand movements. Interestingly, the time increments were almost equivalent in these two functionally distinct motor systems. The durations of error-correcting (closed-loop) movements also increased significantly with aging in both motor systems. These increases suggest that the aging effects are the manifestation of impairment in the sensory process.     

Motor control in simple bimanual movements: a transcranial magnetic stimulation and reaction time study.

OBJECTIVE: Simple reaction time (RT) can be influenced by transcranial magnetic stimulation (TMS) to the motor cortex. Since TMS differentially affects RT of ipsilateral and contralateral muscles a combined RT and TMS investigation sheds light on cortical motor control of bimanual movements. METHODS: Ten normal subjects and one subject with congenital mirror movements (MM) were investigated with a RT paradigm in which they had to move one or both hands in response to a visual go-signal. Suprathreshold TMS was applied to the motor cortex ipsilateral or contralateral to the moving hand at various interstimulus intervals (ISIs) after presentation of the go-signal. EMG recordings from the thenar muscles of both hands were used to determine the RT. RESULTS: TMS applied to the ipsilateral motor cortex shortened RT when TMS was delivered simultaneously with the go-signal. With increasing ISI between TMS and go-signal the RT was progressively delayed. This delay was more pronounced if TMS was applied contralateral to the moving hand. When normal subjects performed bimanual movements the TMS-induced changes in RT were essentially the same as if they had used the hand in an unimanual task. In the subject with MM, TMS given at the time of the go-signal facilitated both the voluntary and the MM. With increasing ISI, however, RT for voluntary movements and MM increased in parallel. CONCLUSIONS: Ipsilateral TMS affects the timing of hand movements to the same extent regardless of whether the hand is engaged in an unimanual or a bimanual movement. It can be concluded, therefore, that in normal subjects simple bimanual movements are controlled by each motor cortex independently. The results obtained in the subject with MM are consistent with the hypothesis that mirror movements originate from uncrossed corticospinal fibres. The alternative hypothesis that a deficit in transcallosal inhibition leads to MM in the contralateral motor cortex is not compatible with the presented data, because TMS applied to the motor cortex ipsilateral to a voluntary moved hand affected voluntary movements and MM to the same extent.     

Ipsilateral motor cortex activation by unaffected hand movements in patients with cerebral infarct

Many studies have reported that stroke patients can be accompanied by motor deficit of the unaffected extremities as well as the affected extremities. This suggests that neural control of motor function of unaffected extremities might be changed following stroke. However, very little is known about this topic. Using functional MRI (fMRI), we investigated changes in neural control of motor function of the unaffected hand in hemiparetic patients with cerebral infarct. Thirty-five hemiparetic stroke patients were recruited for this study. fMRI was performed at 1.5T during either affected or unaffected hand flexion-extension movements. We evaluated motor function of the affected upper extremity using the upper Motricity index (UMI) and the medical research council (MRC) scale for finger extensor. From fMRI, LI (laterality index) was calculated for assessment of relative activity in the ipsilateral versus the contralateral primary sensorimotor cortex. Positive correlation between LIs was observed during affected and unaffected hand movements (r=0.670, p=0.000). LI of unaffected hand movements was also correlated with the affected UMI (r=0.408, p=0.015) and MRC of the affected hand extensor (r=0.362, p=0.033). We demonstrated that the ipsilateral (affected) motor cortex was recruited by unaffected hand movements in proportion to poor motor function of the affected upper extremity.     

Movement-related potentials and control of associated movements

Previous studies have shown a relationship of the readiness potential (RP) preceding a motor act to motor control, as indexed by eye movement (EM). Greater EM and, therefore, less motor control was associated with increased positivity in preresponse RP components. It was hypothesized that these positive components may reflect processes involved in the inhibition of extraneous or associated movement during the performance of a motor act, especially in younger subjects with less motor development. We developed a finger lift task for detecting irrelevant associated movements (AM) from the responding hand and the nonresponding contralateral hand. During each target finger lift, small movements of the other nontarget fingers from the target hand and the contralateral hand were considered movements that should have been inhibited. Trials for each subject were divided into two bins: associated movement (AM) trials which had movement of target plus nontarget fingers, and trials with only target finger movement detected (NAM). Difference waveforms indicated a positive-going shift on trials with discrete target finger movements (NAM). Age and RP positivity at ipsilateral and posterior regions were significantly correlated. We suggest that, on trials on which associated movements are successfully inhibited, the negativity of the RP is confounded by an overlapping slow positivity. The positivity may be related to the effort needed to inhibit associated movements in order to perform a sharper and more discrete response. This relationship is a function of motor control and, indirectly, of age.     

Corticospinal excitability is specifically modulated by motor imagery: a magnetic stimulation study

Transcranial magnetic stimulation (TMS) was used to investigate whether the excitability of the corticospinal system is selectively affected by motor imagery. To this purpose, we performed two experiments. In the first one we recorded motor evoked potentials from right hand and arm muscles during mental simulation of flexion/extension movements of both distal and proximal joints. In the second experiment we applied magnetic stimulation to the right and the left motor cortex of subjects while they were imagining opening or closing their right or their left hand. Motor evoked potentials (MEPs) were recorded from a hand muscle contralateral to the stimulated cortex. The results demonstrated that the excitability pattern during motor imagery dynamically mimics that occurring during movement execution. In addition, while magnetic stimulation of the left motor cortex revealed increased corticospinal excitability when subjects imagined ipsilateral as well as contralateral hand movements, the stimulation of the right motor cortex revealed a facilitatory effect induced by imagery of contralateral hand movements only. In conclusion, motor imagery is a high level process, which, however, manifests itself in the activation of those same cortical circuits that are normally involved in movement execution.     

The preparation and execution of saccadic eye and goal-directed hand movements in patients with Parkinson's disease

The oculomotor and manual motor systems were studied in a two-segment movement task in a group of patients with Parkinson's disease and in age matched normal controls. In order to avoid reflexive motor movements the selection of the correct motor sequence was derived from the interpretation of symbolic (coloured) cues. The latencies and dynamics of eye and hand (pointing) movements performed during the first (fixed) movement segment were measured and the planning and execution processes were manipulated by varying the complexity of the second movement segment relative to the first (with regard to direction and amplitude). The results showed that the eye and hand movements made by patients with Parkinson's disease were not impaired in the initiation of the first movement segment. Interestingly, both Parkinson's patients and controls showed increased eye and hand reaction time latencies for the first movement when the second movement was in the direction opposite to the first. This indicates that the complexity of the second movement influences the execution of the first movement, and importantly that complexity affects motor initiation and execution processes in both normal subjects and in patients with Parkinson's disease. The execution of hand movements was found to be impaired in patients with Parkinson's disease as indicated by a reduced peak velocity of manual pointing responses when compared to age matched controls. By contrast, no differences were found in the dynamics of saccadic eye movements. This dissociation is consistent with the notion that the skeletomotor loop passes through the functionally corresponding portions of the basal ganglia independently of the oculomotor loop. Together, these results demonstrate that Parkinson's patients are able to generate multiple non-reflexive eye and hand movements and that the observed (manual) motor deficits are specific to the processes of motor execution.     

Electrical somatosensory stimulation modulates hand motor function in healthy humans

In healthy people, electrical somatosensory stimulation modulates excitability in contralateral cortical motor areas. The question whether this is associated with a change in motor performance is still under debate. The effect of electrical somatosensory stimulation on motor performance of the hand was investigated in 14 healthy right-handed subjects. Subjects performed index finger and hand tapping movements as well as reach-to-grasp movements towards small and large cubes with each hand prior to (baseline condition) and following 2-hour electrical somatosensory stimulation (trains of 5 pulses at 10 Hz with 1 ms duration delivered at 1 Hz with an intensity on average 60 % above the individual somatosensory threshold) of the (i) right median nerve, (ii) left median nerve, (iii) right tibial nerve (control stimulation) and (iv) left tibial nerve (control stimulation) on separate occasions at least one week apart. The order of sessions was counterbalanced across subjects. Somatosensory stimulation of the median nerves, but not of the tibial nerves, reduced the frequency and velocity of index finger and hand tapping movements performed with the stimulated hand, compared to baseline. In contrast, the kinematics of reach-to-grasp movements remained unaffected by somatosensory stimulation. The data suggest that somatosensory stimulation interferes with the processing of highly automated open-loop motor output at the stimulated limb, as reflected by tapping movements, but not with the processing of closed-loop motor performance, as reflected by reach-to-grasp movements.     

Involvement of area MT in bimanual finger movements in left-handers: an fMRI study

The ease with which humans are able to perform symmetric movements of both hands has traditionally been attributed to the preference of the motor system to activate homologous muscles. Recently, we have shown in right-handers, however, that bimanual index finger adduction and abduction movements in incongruous hand orientations (one palm down/other up) preferentially engaged parietal perception-associated brain areas. Here, we used functional magnetic resonance imaging to investigate the influence of hand orientation in left-handers on cerebral activation during bimanual index finger movements. Performance in incongruous orientation of either hand yielded activations involving right and left motor cortex, supplementary motor area in right superior frontal gyrus (SMA and pre-SMA), bilateral premotor cortex, prefrontal cortex, bilateral somatosensory cortex and anterior parietal cortex along the intraparietal sulcus. In addition, the occipito-temporal cortex corresponding to human area MT (hMT) in either hemisphere was activated in relation to bimanual index finger movements in the incongruous hand orientation as compared with the same movements in the congruous hand orientation or with simply viewing the pacing stimuli. Comparison with the same movement condition in right-handed subjects from a former study support these hMT activations exclusively for left-handed subjects. These results suggest that left-handers use visual motion imagery in guiding incongruous bimanual finger movements.     

Advance movement preparation of eye, foot, and hand: a comparative study using movement-related brain potentials

The present study was designed to test the inter-relationship between generalized motor programs (GMPs) and movement preparation by asking participants to perform movements with eye, foot, or hand. In two independent experiments a response precuing task was employed that combined the recording of movement-related brain potentials (MRPs) with dipole source analysis. Behavioral results indicated the utilization of advance information about movement direction and effector. When eye and hand movements were involved (experiment1) partial advance information about response side but not effector induced parallel motor programming of eye and hand at an abstract but not effector-specific level. In contrast, when partial precues specified side of a forthcoming hand or foot movement (experiment 2) foot and hand were prepared in parallel both at abstract and at effector-specific levels of motor programming. Consistent with the GMP view, these results indicate that effector-specific preparation is possible even when the effector is not yet known as long as a common motor program controls the demanded movements. However, because parallel specification of divergent movement pattern (eye, hand) at an abstract level was not predicted by the GMP, we propose a model of advance movement preparation that takes into account neurofunctional considerations.     

Motor representation in patients rapidly recovering after stroke: a functional magnetic resonance imaging and transcranial magnetic stimulation study

OBJECTIVE: Neuroimaging studies have suggested an evolution of the brain activation pattern in the course of motor recovery after stroke. Initially poor motor performance is correlated with an recruitment of the uninjured hemisphere that continuously vanished until a nearly normal (contralateral) activation pattern is achieved and motor performance is good. Here we were interested in the early brain activation pattern in patients who showed a good and rapid recovery after stroke. METHODS: Ten patients with first-ever ischemic stroke affecting motor areas had to perform self-paced simple or more complex movements with the affected or the unaffected hand during functional magnetic resonance imaging (fMRI). The location and number of activated voxels above threshold were determined. To study possible changes in the cortical motor output map the amplitude of the motor evoked potentials (MEP) and the extent of the excitable area were determined using transcranial magnetic stimulation (TMS). RESULTS: The pattern of activation observed with movements of the affected and the unaffected hand was similar. In the simple motor task significant (P<0.05) increases were found in the primary motor cortex ipsilateral to the movement, the supplementary motor area and the cerebellar hemisphere contralateral to the movement during performance with the affected hand compared to movements with the unaffected hand. When comparing simple with more complex movements performed with either the affected or the unaffected hand, a further tendency to increased activation in motor areas was observed. The amplitude of MEPs obtained from the affected hemisphere was smaller and the extent of cortical output maps was decreased compared to the unaffected hemisphere; but none of the patients showed MEPs at the affected hand when the ipsilateral unaffected motor cortex was stimulated. CONCLUSIONS: Despite a rapid and nearly complete motor recovery the brain activation pattern was associated with increased activity in (bilateral) motor areas as revealed with fMRI. TMS revealed impaired motor output properties, but failed to demonstrate ipsilateral motor pathways. Successful recovery in our patients may therefore rely on the increased bilateral activation of existing motor networks spared by the injury.     

Distinct cortical areas for motor preparation and execution in human identified by Bereitschaftspotential recording and ECoG-EMG coherence analysis.

OBJECTIVE: To clarify the cortical areas involved in motor preparation and execution by investigating Bereitschaftspotentials (BPs) and electrocorticogram-electromyogram (ECoG-EMG) coherence from subdural electrodes placed around the rolandic area. METHODS: BPs and ECoG-EMG coherence were investigated for presurgical evaluation in a patient with cavernoma in the left frontal lobe. BPs were recorded in association with the tongue, right hand and right foot movements. ECoG-EMG coherence was calculated in association with weak muscle contraction of the right hand. RESULTS: Two cortical areas related to voluntary motor control were identified; one in the primary hand motor area, which generated surface-negative BPs with hand movements and showed significant coherence of ECoG with EMG of the contralateral hand muscle, and the other in the ventral rolandic area posterior to the central sulcus, which generated surface-positive BPs with voluntary movements of multiple sites (hand, tongue and foot) but did not show any ECoG-EMG coherence. CONCLUSIONS: It is postulated that the former area represents the primary motor area involved in both motor preparation and execution, and the latter area represents the non-primary motor area involved in motor preparation. SIGNIFICANCE: BP recording combined with ECoG-EMG coherence analysis could reveal the functional roles of motor cortices and the reorganization induced by structural brain lesion.     

Ipsilateral corticospinal projections do not predict congenital mirror movements: a case report

Congenital mirror movements (CMMs) are involuntary, symmetric movements of one hand during the production of voluntary movements with the other. CMMs have been attributed to a range of physiological mechanisms, including excessive ipsilateral projections from each motor cortex to distal extremities. We examined this hypothesis with an individual showing pronounced CMMs. Mirror movements were characterized for a set of hand muscles during a simple contraction task. Transcranial magnetic stimulation (TMS) was then used to map the relative input to each muscle from both motor cortices. Contrary to our expectations, CMMs were most prominent for muscles with the strongest contralateral representation rather than in muscles that were activated by stimulation of either hemisphere. These findings support a bilateral control hypothesis whereby CMMs result from the recruitment of both motor cortices during intended unimanual movements. Consistent with this hypothesis, bilateral motor cortex activity was evident during intended unimanual movements in an fMRI study. To assess the level at which bilateral recruitment occurs, motor cortex excitability during imagined unimanual movements was assessed with TMS. Facilitory excitation was only observed in the contralateral motor cortex. Thus, the bilateral recruitment of the hemispheres for unilateral actions in individuals with CMMs appears to occur during movement execution rather than motor planning.     

The dorsal premotor cortex orchestrates concurrent speech and fingertapping movements

Human speech and hand use both involve highly specialized complex movement patterns. Whereas previous studies in detail characterized the cortical motor systems mediating speech and finger movements, the network that provides coordination of concurrent speech and hand movements so far is unknown. Using functional magnetic resonance imaging (fMRI), the present study investigated differential cortical networks devoted to speech or fingertapping, and regions mediating integration of these complex movement patterns involving different effectors. The conjunction contrasts revealing regions activated both during sole fingertapping and sole repetitive articulation or reading aloud showed contralateral regions at the border of ventral and dorsal motor cortex. In contrast, the analyses revealing regions showing a higher level of fMRI activation for concurrent movements of both effectors compared with sole hand movements or repetitive articulation or reading aloud showed distinct premotor activations, which were situated dorsal and caudal to the areas activated across speech and fingertapping tasks. These results indicate that the premotor cortex (PMC) subserves coordination of concurrent speech with hand movements. This integrative motor region is not identical with the area that shows overlapping activations for speech and fingertapping. Thus, concurrent performance of these complex movement patterns involving different effectors requires, in addition to somatotopic motor cortex activation, orchestration subserved by a distinct PMC area.     

Targeted tDCS selectively improves motor adaptation with the proximal and distal upper limb

BackgroundThe cerebellum and primary motor cortex (M1) are crucial to coordinated and accurate movements of the upper limbs. There is also appreciable evidence that these two structures exert somewhat divergent influences upon proximal versus distal upper limb control. Here, we aimed to differentially regulate the contribution of the cerebellum and M1 to proximal and distal effectors during motor adaptation, with transcranial direct current stimulation (tDCS). For this, we employed tasks that promote similar motor demands, but isolate whole arm from hand/finger movements, in order to functionally segregate the hierarchy of upper limb control.MethodsBoth young and older adults took part in a visuomotor rotation task; where they adapted to a 60° visuomotor rotation using either a hand-held joystick (requiring finger/hand movements) or a 2D robotic manipulandum (requiring whole-arm reaching movements), while M1, cerebellar or sham tDCS was applied.ResultsWe found that cerebellar stimulation improved adaptation performance when arm movements were required to complete the task, while in contrast stimulation of M1 enhanced adaptation during hand and finger movements only. This double-dissociation was replicated in an independent group of older adults, demonstrating that the behaviour remains intact in ageing.ConclusionsThese results suggest that stimulation of distinct motor areas can selectively improve motor adaptation in the proximal and distal upper limb. This also highlights new ways in which tDCS might be best applied to achieve reliable rehabilitation of upper limb motor deficits.     

Influence of mirror therapy on human motor cortex

This article investigates whether or not mirror therapy alters the neural mechanisms in human motor cortex. Six healthy volunteers participated. The study investigated the effects of three main factors of mirror therapy (observation of hand movements in a mirror, motor imagery of an assumed affected hand, and assistance in exercising the assumed affected hand) on excitability changes in the human motor cortex to clarify the contribution of each factor. The increase in motor-evoked potential (MEP) amplitudes during motor imagery tended to be larger with a mirror than without one. Moreover, MEP amplitudes increased greatly when movements were assisted. Watching the movement of one hand in a mirror makes it easier to move the other hand in the same way. Moreover, the increase in MEP amplitudes is related to the synergic effects of afferent information and motor imagery.     

INFLUENCE OF MIRROR THERAPY ON HUMAN MOTOR CORTEX

This article investigates whether or not mirror therapy alters the neural mechanisms in human motor cortex. Six healthy volunteers participated. The study investigated the effects of three main factors of mirror therapy (observation of hand movements in a mirror, motor imagery of an assumed affected hand, and assistance in exercising the assumed affected hand) on excitability changes in the human motor cortex to clarify the contribution of each factor. The increase in motor-evoked potential (MEP) amplitudes during motor imagery tended to be larger with a mirror than without one. Moreover, MEP amplitudes increased greatly when movements were assisted. Watching the movement of one hand in a mirror makes it easier to move the other hand in the same way. Moreover, the increase in MEP amplitudes is related to the synergic effects of afferent information and motor imagery.