Ipsilateral Motor Areas Research Articles

Analysis of brain network differences in the active, motor imagery, and passive stoke rehabilitation paradigms based on the task-state EEG

Different movement paradigms have varying effects on stroke rehabilitation, and their mechanisms of action on the brain are not fully understood. This study aims to investigate disparities in brain network and functional connectivity of three movement paradigms (active, motor imagery, passive) on stroke recovery. EEG signals were recorded from 11 S patients (SP) and 13 healthy controls (HC) during fist clenching and opening tasks under the three paradigms. Brain networks were constructed to analyze alterations in brain network connectivity, node strength (NS), clustering coefficients (CC), characteristic path length (CPL), and small-world index(S). Our findings revealed increased activity in the contralateral motor area in SP and higher activity in the ipsilateral motor area in HC. In the beta band, SP exhibited significantly higher CC in motor imagery (MI) than in active and passive tasks. Furthermore, the small world index of SP during MI tasks in the beta band was significantly smaller than in the active and passive tasks. NS in the gamma band for SP during the MI paradigm was significantly higher than in the active and passive paradigms. These findings suggest reorganization within both ipsilateral and contralateral motor areas of stroke patients during MI tasks, providing evidence for neural restructuring. Collectively, these findings contribute to a deeper understanding of task-state brain network changes and the rehabilitative mechanism of MI on motor function.

Cholinergic modulation of motor sequence learning.

The cholinergic system plays a key role in motor function, but whether pharmacological modulation of cholinergic activity affects motor sequence learning is unknown. The acetylcholine receptor antagonist biperiden, an established treatment in movement disorders, reduces attentional modulation, but whether it influences motor sequence learning is not clear. Using a randomized, double-blind placebo-controlled crossover design, we tested 30 healthy young participants and showed that biperiden impairs the ability to learn sequential finger movements, accompanied by widespread oscillatory broadband power changes (4-25 Hz) in the motor sequence learning network after receiving biperiden, with greater power in the theta, alpha and beta bands over ipsilateral motor and bilateral parietal-occipital areas. The reduced early theta power during a repeated compared with random sequence, likely reflecting disengagement of top-down attention to sensory processes, was disrupted by biperiden. Alpha synchronization during repeated sequences reflects sensory gating and lower visuospatial attention requirements compared with visuomotor responses to random sequences. After biperiden, alpha synchronization was greater, potentially reflecting excessive visuospatial attention reduction, affecting visuomotor responding required to enable sequence learning. Beta oscillations facilitate sequence learning by integrating visual and somatosensory inputs, stabilizing repeated sequences and promoting prediction of the next stimulus. The beta synchronization after biperiden fits with a disruption of the selective visuospatial attention enhancement associated with initial sequence learning. These findings highlight the role of cholinergic processes in motor sequence learning.

Excitatory-inhibitory mismatch shapes node recruitment in an epileptic network.

Focal epilepsy is thought to be a network disease, in which epileptiform activity can spread noncontiguously through the brain via highly interconnected nodes, or hubs, within existing networks. Animal models confirming this hypothesis are scarce, and our understanding of how distant nodes are recruited is also lacking. Whether interictal spikes (IISs) also create and reverberate through a network is not well understood. We injected bicuculline into the S1 barrel cortex and employed multisite local field potential and Thy-1 and parvalbumin (PV) cell mesoscopic calcium imaging during IISs to monitor excitatory and inhibitory cells in two monosynaptically connected nodes and one disynaptically connected node: ipsilateral secondary motor area (iM2), contralateral S1 (cS1), and contralateral secondary motor area (cM2). Node participation was analyzed with spike-triggered coactivity maps. Experiments were repeated with 4-aminopyridine as an epileptic agent. We found that each IIS reverberated throughout the network, differentially recruiting both excitatory and inhibitory cells in all connected nodes. The strongest response was found in iM2. Paradoxically, node cM2, which was connected disynaptically to the focus, was recruited more intensely than node cS1, which was connected monosynaptically. The explanation for this effect could be found in node-specific excitatory/inhibitory (E/I) balance, as cS1 demonstrated greater PV inhibitory cell activation compared with cM2, where Thy-1 excitatory cells were more heavily recruited. Our data show that IISs spread noncontiguously by exploiting fiber pathways that connect nodes in a distributed network and that E/I balance plays a critical role in node recruitment. This multinodal IIS network model can be used to investigate cell-specific dynamics in the spatial propagation of epileptiform activity.

Para-Sports can Promote Functional Reorganization in the Ipsilateral Primary Motor Cortex of Lower Limbs Amputee

Background. Drastic functional reorganization was observed in the ipsilateral primary motor cortex (M1) of a Paralympic long jumper with a unilateral below-knee amputation in our previous study. However, it remains unclear whether long-term para-sports are associated with ipsilateral M1 reorganization since only 1 athlete with amputation was investigated. Objective. This study aimed to investigate the relationship between the long-term para-sports and ipsilateral M1 reorganization after lower limb amputation. Methods. Lower limb rhythmic muscle contraction tasks with functional magnetic resonance imaging and T1-weighted structural imaging were performed in 30 lower limb amputees with different para-sports experiences in the chronic phase. Results. Brain activity in the ipsilateral primary motor and somatosensory areas (SM1) as well as the contralateral dorsolateral prefrontal cortex, SM1, and inferior temporal gyrus showed a positive correlation with the years of routine para-sports participation (sports years) during contraction of the amputated knee. Indeed, twelve of the 30 participants who exhibited significant ipsilateral M1 activation during amputated knee contraction had a relatively longer history of para-sports participation. No significant correlation was found in the structural analysis. Conclusions. Long-term para-sports could lead to extensive reorganization at the brain network level, not only bilateral M1 reorganization but also reorganization of the frontal lobe and visual pathways. These results suggest that the interaction of injury-induced and use-dependent cortical plasticity might bring about drastic reorganization in lower limb amputees.

Event-Related Desynchronization During Mirror Visual Feedback: A Comparison of Older Adults and People After Stroke.

Event-related desynchronization (ERD), as a proxy for mirror neuron activity, has been used as a neurophysiological marker for motor execution after mirror visual feedback (MVF). Using EEG, this study investigated ERD upon the immediate effects of single-session MVF in unimanual arm movements compared with the ERD effects occurring without a mirror, in two groups: stroke patients with left hemiplegia and their healthy counterparts. During EEG recordings, each group performed one session of mirror therapy training in three task conditions: with a mirror, with no mirror, and with a covered mirror. An asymmetry index was calculated from the subtraction of the event-related spectrum perturbations between the C3 and C4 electrodes located over the sensorimotor cortices contralateral and ipsilateral to the moved arm. Results of the effect of task versus group in contralateral and ipsilateral motor areas showed that there was a significant effect of task condition at the contralateral motor area in the high beta band (17–35 Hz) at C3. High beta ERD showed that the suppression was greater over the contralateral hemisphere than it was over the ipsilateral hemisphere in both study groups. The magnitude of low beta (12–16 Hz) ERD in patients with stroke was more suppressed in contralesional C3 under the no mirror compared to that of the covered mirror and similarly more suppressed in ipsilesional C4 ERD under the no mirror compared to that of the mirror condition. The correlation analysis revealed that the magnitude of ERSP power correlated significantly with arm severity in the low and high beta bands in patients with stroke, and a higher asymmetry index in the low beta band was associated with higher arm functioning under the no-mirror condition. There was a shift in sensorimotor ERD toward the contralateral hemisphere as induced by MVF accompanying unimanual movement in both stroke patients and healthy controls. The use of ERD in the low beta band as a neurophysiological marker to indicate the relationships between the amount of MVF-induced ERD attenuation and motor severity, and the outcome indicator for improving stroke patients’ neuroplasticity in clinical trials using MVF are warranted to be explored in the future.

Lateralized EEG mu power during action observation and motor imagery in typically developing children and children with unilateral Cerebral Palsy

ObjectiveDuring motor execution (ME), mu power is diminished over the contralateral hemisphere and increased over the ipsilateral hemisphere, which has been associated with cortical activation of the contralateral motor areas and inhibition of the ipsilateral motor areas respectively. The influence of action observation (AO) and motor imagery (MI) on mu power is less clear, especially in children, and remains to be studied in children with unilateral cerebral palsy (uCP). MethodsWe determined mu power during ME, AO, and MI of 45 typically developing (TD) children and 15 children with uCP over both hemispheres, for each hand. ResultsIn TD children, over the left hemisphere mu power was lowered during ME when the right hand was used. In line, over the right hemisphere mu power was lowered when the left hand was addressed. In addition, during AO and MI increased mu power was observed when the right hand was addressed. In children with uCP, over the spared hemisphere mu power was diminished during ME when the less-affected hand was used. However, over the lesioned hemisphere, no mu changes were observed. ConclusionsThe results of TD children fit the activation/inhibition model of mu power. SignificanceThe results of children with uCP suggest that the lesioned hemisphere is unresponsive to the motor tasks.

Limited capacity for ipsilateral secondary motor areas to support hand function post-stroke.

Ipsilateral-projecting corticobulbar pathways, originating primarily from secondary motor areas, innervate the proximal and even distal portions, although they branch more extensively at the spinal cord. It is currently unclear to what extent these ipsilateral secondary motor areas and subsequent cortical projections may contribute to hand function following stroke-induced damage to one hemisphere. In the present study, we provide both structural and functional evidence indicating that individuals increasingly rely on ipsilateral secondary motor areas, although at the detriment of hand function. Increased activity in ipsilateral secondary motor areas was associated with increased involuntary coupling between shoulder abduction and finger flexion, most probably as a result of the low resolution of these pathways, making it increasingly difficult to open the hand. These findings suggest that, although ipsilateral secondary motor areas may support proximal movements, they do not have the capacity to support distal hand function, particularly for hand opening. Recent findings have shown connections of ipsilateral cortico-reticulospinal tract (CRST), predominantly originating from secondary motor areas to not only proximal, but also distal muscles of the arm. Following a unilateral stroke, CRST from the ipsilateral side remains intact and thus has been proposed as a possible backup system for post-stroke rehabilitation even for the hand. We argue that, although CRST from ipsilateral secondary motor areas can provide control for proximal joints, it is insufficient to control either hand or coordinated shoulder and hand movements as a result of its extensive spinal branching compared to contralateral corticospinal tract. To address this issue, we combined magnetic resonance imaging, high-density EEG, and robotics in 17 individuals with severe chronic hemiparetic stroke and 12 age-matched controls. We tested for changes in structural morphometry of the sensorimotor cortex and found that individuals with stroke demonstrated higher grey matter density in secondary motor areas ipsilateral to the paretic arm compared to controls. We then measured cortical activity when participants were attempting to generate hand opening either supported on a table or when lifting against a shoulder abduction load. The addition of shoulder abduction during hand opening increased reliance on ipsilateral secondary motor areas in stroke, but not controls. Crucially, the increased use of ipsilateral secondary motor areas was associated with decreased hand opening ability when lifting the arm as a result of involuntary coupling between the shoulder and wrist/finger flexors. Taken together, this evidence implicates a compensatory role for ipsilateral (i.e. contralesional) secondary motor areas post-stroke, although with no apparent capacity to support hand function.

Modulatory effects of the supplementary motor area on primary motor cortex outputs.

Premotor areas of primates are specialized cortical regions that can contribute to hand movements by modulating the outputs of the primary motor cortex (M1). The goal of the present work was to study how the supplementary motor area (SMA) located within the same hemisphere [i.e., ipsilateral SMA (iSMA)] or the opposite hemisphere [i.e., contralateral (cSMA)] modulate the outputs of M1. We used paired-pulse protocols with intracortical stimulations in sedated capuchin monkeys. A conditioning stimulus in iSMA or cSMA was delivered simultaneously or before a test stimulus in M1 with different interstimulus intervals (ISIs) while electromyographic activity was recorded in hand and forearm muscles. The pattern of modulation from iSMA and cSMA shared some clear similarities. In particular, both areas predominantly induced facilitatory effects on M1 outputs with shorter ISIs and inhibitory effects with longer ISIs. However, the incidence and strength of facilitatory effects were greater for iSMA than cSMA. We then compared the pattern of modulatory effects from SMA to the ones from the dorsal and ventral premotor cortexes (PMd and PMv) collected in the same series of experiments. Among premotor areas, the impact of SMA on M1 outputs was always weaker than the one of either PMd or PMv, and this was regardless of the hemisphere, or the ISI, tested. These results show that SMA exerts a unique set of modulations on M1 outputs, which could support its specific function for the production of hand movements.NEW & NOTEWORTHY We unequivocally isolated stimulation to either the ipsilateral or contralateral supplementary motor area (SMA) using invasive techniques and compared their modulatory effects on the outputs of primary motor cortex (M1). Modulations from both SMAs shared many similarities. However, facilitatory effects evoked from ipsilateral SMA were more common and more powerful. This pattern differs from the ones of other premotor areas, which suggests that each premotor area makes unique contributions to the production of motor outputs.

An electrophysiological study of Congenital Mirror Movements

Congenital mirror movements (CMM) are a curious and rare neurological disorder in which volitional movements of a limb are accompanied by simultaneous involuntary symmetrical movements in the contralateral one. We performed an electrophysiological study of a young man with CMM. Our patient had bilateral CMM, graded 3 on the Wood and Teuber scale. Transcranial magnetic stimulation (TMS) was performed on the left and right motor cortex (M1). Surface EMG - was obtained by the right and left FSD and ECD muscles at rest and when performing self-paced repetitive flexion–extension of the fingers. Moreover we obtained a map of M1 using an MRI-navigated transcranial magnetic stimulation device (nTMS). Bilateral motor evocated potentials (MEPs) were recorded from FDI muscles when stimulating each M1. The mean ipsilateral MEP amplitude when stimulating the left M1 was higher than the contralateral one. The surface-EMG recording mirrored the clinical findings, demonstrating simultaneous bilateral bursts of EMG activity when performing unilateral flexion or extension movements. Ipsilateral and contralateral motor area maps, obtained with nTMS, were comparable. Our finding confirm that ipsilateral and contralateral MEPs are originated in the same cortical areas. Moreover, this is the first reported navigated TMS brain mapping of patient affected by CMM.

Prediction of recovery from supplementary motor area syndrome after brain tumor surgery: preoperative diffusion tensor tractography analysis and postoperative neurological clinical course.

OBJECTIVE Previous studies have suggested a correlation between interhemispheric sensorimotor networks and recovery from supplementary motor area (SMA) syndrome. In the present study, the authors examined the hypothesis that interhemispheric connectivity of the primary motor cortex in one hemisphere with the contralateral SMA may be important in the recovery from SMA syndrome. Further, they posited that motor cortical fiber connectivity with the SMA is related to the severity of SMA syndrome. METHODS Patients referred to the authors' neurological surgery department were retrospectively analyzed for this study. All patients with tumors involving the unilateral SMA region, without involvement of the primary motor area, and diagnosed with SMA syndrome in the postoperative period were eligible for inclusion. Preoperative diffusion tensor imaging tractography (DTT) was used to examine the number of fiber tracts (NFidx) connecting the contralateral SMA to the ipsilateral primary motor area via the corpus callosum. Complete neurological examination had been performed in all patients in the pre- and postoperative periods. All patients were divided into two groups: those who recovered from SMA syndrome in ≤ 7 days (early recovery group) and those who recovered in ≥ 8 days (late recovery group). Differences between the two groups were assessed using the Student t-test and the chi-square test. RESULTS Eleven patients (10 men, 1 woman) were included in the study. All patients showed transient postoperative motor deficits because of SMA syndrome. Tractography data revealed NFidx from the contralateral SMA to the ipsilateral primary motor area via the corpus callosum. The mean tumor volume (early 27.87 vs late 50.91 cm3, p = 0.028) and mean NFidx (early 8923.16 vs late 4726.4, p = 0.002) were significantly different between the two groups. Fisher exact test showed a significant difference in the days of recovery from SMA syndrome between patients with an NFidx > 8000 and those with an NFidx < 8000. CONCLUSIONS Diffusion tensor imaging tractography may be useful for predicting the speed of recovery from SMA syndrome. To the authors' knowledge, this is the first DTT study to identify interhemispheric connectivity of the SMA in patients with brain tumors.

Changes in hemodynamic responses during movements of the upper extremities in the acute phase after stroke: A fNIRS study

The acute phase of stroke is accompanied by functional changes and interplay of both hemispheres. However little is known on how the time course of functional motor recovery is related to the progression of symmetry in the motor areas of the brain. This study aimed to assess the time course of both hemodynamic patterns of cortical motor areas using functional near infrared spectroscopy (fNIRS) and functional recovery during the first months after stroke. Unaffected upper limb movements-related contralateral motor areas activity showed no significant changes. Eight right-handed first ischemic/hemorrhagic stroke patients (60 ± 8 yrs, 3 female and 5 men) with mild to severe hemiparesis were examined with fNIRS measurements and functional motor recovery (Fugl-Meyer score) tests every two weeks during two months (five sessions). We investigated hemodynamic changes over the contralateral and ipsilateral motor areas with a 2 × 8-channel fNIRS system (Oxymon MkIII ® ) during a unilateral intermittent isometric forearm task (1 Hz) at self-selected submaximal force levels. Laterality index (LI) was computed to evaluate the asymmetry of hemodynamic changes from the two hemispheres. Affected upper limb movements were associated early with a bilateral cortical activity before shifting to contralateral patterns ( P < 0.01). Progressive lateralization was observed with LI increases over the first 4 sessions (from −0.24 ± 0.18 to 0.36 ± 0.27, P < 0.05) prior to level off (session 5, 0.25 ± 0.39), as did the Fugl-Meyer score. These findings suggest that cortical reorganization monitoring with fNIRS during the first weeks after stroke should be considered further when assessing functional motor recovery in stroke rehabilitation services.

Effector-Invariant Movement Encoding in the Human Motor System.

Ipsilateral motor areas of cerebral cortex are active during arm movements and even reliably predict movement direction. Is coding similar during ipsilateral and contralateral movements? If so, is it in extrinsic (world-centered) or intrinsic (joint-configuration) coordinates? We addressed these questions by examining the similarity of multivoxel fMRI patterns in visuomotor cortical regions during unilateral reaching movements with both arms. The results of three complementary analyses revealed that fMRI response patterns were similar across right and left arm movements to identical targets (extrinsic coordinates) in visual cortices, and across movements with equivalent joint-angles (intrinsic coordinates) in motor cortices. We interpret this as evidence for the existence of distributed neural populations in multiple motor system areas that encode ipsilateral and contralateral movements in a similar manner: according to their intrinsic/joint coordinates.SIGNIFICANCE STATEMENT Cortical motor control exhibits clear lateralization: each hemisphere controls the motor output of the contralateral body. Nevertheless, neural populations in ipsilateral areas across the visuomotor hierarchy are active during unilateral movements. We show that fMRI response patterns in the motor cortices are similar for both arms if the movement direction is mirror-reversed across the midline. This suggests that in both ipsilateral and contralateral motor cortices, neural populations have effector-invariant coding of movements in intrinsic coordinates. This not only affects our understanding of motor control, it may serve in the development of brain machine interfaces that also use ipsilateral neural activity.

Cooperation Not Competition: Bihemispheric tDCS and fMRI Show Role for Ipsilateral Hemisphere in Motor Learning.

What is the role of ipsilateral motor and premotor areas in motor learning? One view is that ipsilateral activity suppresses contralateral motor cortex and, accordingly, that inhibiting ipsilateral regions can improve motor learning. Alternatively, the ipsilateral motor cortex may play an active role in the control and/or learning of unilateral hand movements. We approached this question by applying double-blind bihemispheric transcranial direct current stimulation (tDCS) over both contralateral and ipsilateral motor cortex in a between-group design during 4 d of unimanual explicit sequence training in human participants. Independently of whether the anode was placed over contralateral or ipsilateral motor cortex, bihemispheric stimulation yielded substantial performance gains relative to unihemispheric or sham stimulation. This performance advantage appeared to be supported by plastic changes in both hemispheres. First, we found that behavioral advantages generalized strongly to the untrained hand, suggesting that tDCS strengthened effector-independent representations. Second, functional imaging during speed-matched execution of trained sequences conducted 48 h after training revealed sustained, polarity-independent increases in activity in both motor cortices relative to the sham group. These results suggest a cooperative rather than competitive interaction of the two motor cortices during skill learning and suggest that bihemispheric brain stimulation during unimanual skill learning may be beneficial because it harnesses plasticity in the ipsilateral hemisphere.SIGNIFICANCE STATEMENT Many neurorehabilitation approaches are based on the idea that is beneficial to boost excitability in the contralateral hemisphere while attenuating that of the ipsilateral cortex to reduce interhemispheric inhibition. We observed that bihemispheric transcranial direct current stimulation (tDCS) with the excitatory anode either over contralateral or ipsilateral motor cortex facilitated motor learning nearly twice as strongly as unihemispheric tDCS. These increases in motor learning were accompanied by increases in fMRI activation in both motor cortices that outlasted the stimulation period, as well as increased generalization to the untrained hand. Collectively, our findings suggest a cooperative rather than a competitive role of the hemispheres and imply that it is most beneficial to harness plasticity in both hemispheres in neurorehabilitation of motor deficits.

P158 The role of ipsilateral motor areas in hand motor function – Insights from online TMS

Background Event-related transcranial magnetic stimulation (TMS) allows to interfere with neural processing of cortical areas. While we have a rather good knowledge of the role of frontoparietal areas for motor performance of the contralateral hand, the contribution of ipsilateral areas is far less understood (Davare et al., 2007) . Neuroimaging studies found an increasing recruitment of ipsilateral motor regions in healthy elderly, implying a supportive influence during normative aging Hutchinson et al., 2002 , Riecker et al., 2006 . To test this hypothesis, we used online-TMS to investigate the role of ipsilateral primary motor cortex (M1), premotor cortex (dPMC), and the anterior intraparietal sulcus (aIPS) in motor tasks of different complexity in young and elderly subjects. Methods 30 healthy, right-handed subjects (15 young (27.8 y); 15 elderly (61.3 y)) conducted four motor tasks of different complexity: (i) simple reaction time task, (ii) maximum finger and (iii) hand tapping frequencies, and (iv) rapid pointing between two defined targets. Tapping and pointing tasks were recorded with kinematic motion analyzer system (Zebris). TMS pulses were applied as 10 Hz-trains, time-locked to task execution. Stimulation was applied at 90% intensity of the resting motor threshold (rMT) to ipsilateral M1, dPMC, and aIPS. Sham-stimulation at 90% of rMT to parieto-occipital vertex served as control condition. Results In the finger tapping task (ii) we found both a main effect of online-TMS and an interaction effect between group and stimulation site. While in elderly stimulation over dPMC led to a decrease in tapping intervall, performance in the young group was mainly affected by M1-stimulation. Furthermore, for the target pointing task (iv) we found a decrease of aiming accuracy in the elderly group upon TMS interference with aIPS and dPMC but the young stayed unaffected by stimulation over all sites. Finally, age correlated with a frequency reduction of hand tapping (iii) induced by aIPS-stimulation. Conclusion Our findings suggest that there are differential roles of investigated areas in motor performance in aging. The data further displays relevance of dPMC and aIPS in repetitive tapping and target pointing tasks in elderly. Both regions seem to be causally engaged in maintaining performance in elderly. This might indicate that an increasing recruitment of ipsilateral motor regions Hutchinson et al., 2002 , Riecker et al., 2006 seems to have a supportive influence on motor performance in elderly.

EPV 9. The role of ipsilateral motor areas in hand motor function in healthy ageing – Insights from online TMS

Background Event-related (“online”) transcranial magnetic stimulation (TMS) allows to interfere with neural processing of distinct cortical areas. While we have a rather good knowledge on the role of frontoparietal areas for motor performance of the contralateral hand, the contribution of areas in the hemisphere ipsilateral to the moving hand is far less understood ( [Davare et al., 2007] , [Vollmer et al., 2015] ). For example, neuroimaging studies found an increasing ipsilateral recruitment of motor regions in healthy eldery subjects, implying a supportive influence during normative ageing ( [Hutchinson et al., 2002] , [Riecker et al., 2006] ). To test this hypothesis, we used online-TMS to investigate the role of ipsilateral primary motor cortex (M1), premotor cortex (dPMC) and anterior intraparietal sulcus (aIPS) in motor tasks of different complexity in young and elderly subjects. Methods Young (range: 20–30 years) and elderly (range: 50–70 years) healthy, right-handed subjects conducted four motor tasks of different complexity with their right hand: (i) simple reaction time, (ii) maximum finger and (iii) hand tapping frequencies and (iv) rapid pointing between two defined targets. Tapping and pointing tasks were measured with kinematic, three-dimensional recordings using an ultrasound motion analyzer system (Zebris). TMS pulses were applied as 10 Hz-trains time-locked to task execution. Stimulation was applied at 90% of resting motor threshold (rMT) to ipsilateral M1, dPMC and aIPS. Sham-stimulation at 90% of rMT to parieto-occipital vertex served as control condition. Results Online-TMS applied to ipsilateral M1 led to a significant response slowing and to a significantly increased coeffcient of variation in the simple reaction time task in elderly subjects. In contrast, performance of more complex motor tasks was not affected by ipsilateral M1-stimulation. TMS applied to the ipsilateral dPMC or aIPS affected the more complex motor tasks. DPMC-stimulation caused a reduction of tapping amplitude and a significant reduction of overall performance in the finger tapping task. TMS applied to the aIPS led to a significant reduction of tapping amplitude and tended to reduce overall performance in the hand tapping task. Furthermore, subjects showed a significant decrease of aiming accuracy in the pointing task, upon TMS interference with ipsilateral dPMC as well as aIPS in elderly subjects. Finally, within the group of elderly subjects, age strongly correlated with a frequency reduction of hand tapping induced by both M1- and aIPS-stimulation. Conclusion Consistent with previous work ( Vollmer et al., 2015 ), our findings underline the impact of ipsilateral M1 on simple motor task. We also show that in eldery subjects ipsilateral dPMC as well as ipsilateral aIPS seem to be causally engaged in maintaining performance in more complex motor tasks. These findings agree with neuroimaging studies indicating the IPS’ particular involvement in visuomotor tasks ( Grefkes et al., 2006 ). Of note, our results support the notion of age-dependent recruitment of ipsilateral M1 in motor tasks ( [Hutchinson et al., 2002] , [Riecker et al., 2006] ) and suggest a similar relevance of aIPS for motor performance in healthy ageing individuals.

Motor cortex activation during motor imagery of the upper limbs in stroke patients

ABSTRACT Objective: The objective of this study was to analyze the functional brain activation in acute stroke patients during motor execution (ME) and motor imagery (MI) and to discuss the association between damaged brain structure and impaired brain function in stroke patients. Methods: The functional magnetic resonance imaging technique was used to observe activation of the brain during ME/MI of the upper limbs in 12 acute stroke patients (with the left brain damage) and 12 healthy controls. Results: During ME, the stroke patients appeared to be activated more strongly than the healthy controls in the ipsilateral primary motor areas. The MI of the affected hand in the stroke patients was not significantly different from that of the healthy hand. The nonmotor areas, the angular gyrus, and the fusiform gyrus were also activated during ME/MI. Conclusion: Structural damage in the brain is associated with the activation of brain function in acute stroke patients. Ipsilateral inhibition is reduced in stroke patients during ME and the damaged brain needs to recruit more brain areas to complete the desired action due to motion difficulties resulting from brain damage. The participation of nonmotor brain areas in ME/MI indicates that cortical reorganization may contribute to the restoration of motor function following stroke. MI can be used to improve injured brain areas, helping with the rehabilitation of stroke patients.

3D Cortical electrophysiology of ballistic upper limb movement in humans

Precise motor control requires the ability to scale the parameters of movement. Theta oscillations across the cortex have been associated with changes in memory, attention, and sensorimotor processing. What has proven more elusive is pinpointing the region-specific frequency band oscillations that are associated with specific parameters of movement during the acceleration and deceleration phases. We report a study using 3D analytic techniques for high density electroencephalography that examines electrocortical dynamics while participants produce upper limb movements to different distances at varying rates. During fast ballistic movements, we observed increased theta band activity in the left motor area contralateral to the moving limb during the acceleration phase of the movement, and theta power correlated with the acceleration of movement. In contrast, beta band activity scaled with the type of movement during the deceleration phase near the end of the movement and correlated with movement time. In the ipsilateral motor and somatosensory area, alpha band activity decreased with the type of movement near the end of the movement, and gamma band activity in visual cortex increased with the type of movement near the end of the movement. Our results suggest that humans use distinct lateralized cortical activity for distance and speed dependent arm movements. We provide new evidence that a temporary increase in theta band power relates to movement acceleration and is important during movement execution. Further, the theta power increase is coupled with desychronization of beta band power and alpha band power which are modulated by the task near the end of movement.

Anodal transcranial direct current stimulation of the motor cortex induces opposite modulation of reciprocal inhibition in wrist extensor and flexor.

Transcranial direct current stimulation (tDCS) is used as a noninvasive tool to modulate brain excitability in humans. Recently, several studies have demonstrated that tDCS applied over the motor cortex also modulates spinal neural network excitability and therefore can be used to explore the corticospinal control acting on spinal neurons. Previously, we showed that reciprocal inhibition directed to wrist flexor motoneurons is enhanced during contralateral anodal tDCS, but it is likely that the corticospinal control acting on spinal networks controlling wrist flexors and extensors is not similar. The primary aim of the study was to explore the effects of anodal tDCS on reciprocal inhibition directed to wrist extensor motoneurons. To further examine the supraspinal control acting on the reciprocal inhibition between wrist flexors and extensors, we also explored the effects of the tDCS applied to the ipsilateral hand motor area. In healthy volunteers, we tested the effects induced by sham and anodal tDCS on reciprocal inhibition pathways innervating wrist muscles. Reciprocal inhibition directed from flexor to extensor muscles and the reverse situation, i.e., reciprocal inhibition, directed from extensors to flexors were studied in parallel with the H reflex technique. Our main finding was that contralateral anodal tDCS induces opposing effects on reciprocal inhibition: it decreases reciprocal inhibition directed from flexors to extensors, but it increases reciprocal inhibition directed from extensors to flexors. The functional result of these opposite effects on reciprocal inhibition seems to favor wrist extension excitability, suggesting an asymmetric descending control onto the interneurons that mediate reciprocal inhibition.

White matter integrity of motor connections related to training gains in healthy aging

Impaired motor skill acquisition is a feature of older age. Acquisition of new motor skills requires the interplay between different cortical motor areas. Using diffusion tensor imaging we reconstructed cortico-cortical connections between the primary motor cortex (M1) and secondary motor areas in 11 older and 11 young participants who took part in a motor skill acquisition paradigm with the nondominant left hand. Examining the extent to which tract-related integrity correlated with training gains we found that white matter integrity of fibers connecting contralateral M1 with both contralateral (r = 0.85) and ipsilateral supplementary motor areas (r = 0.92) were positively associated in old participants. Also, fibers connecting contralateral M1 with ipsilateral dorsal premotor (r = 0.82) and fibers connecting ipsilateral dorsal premotor and supplementary motor area (r = 0.88) were positively related to skill acquisition (all p < 0.05). A similar structure-behavior relationship was not present in the young control subjects suggesting a critical role of brain structural integrity for motor learning in healthy aging.

Recruitment of ipsilateral and contralateral upper limb muscles following stimulation of the cortical motor areas in the monkey

It is well established that cortical motor stimulation results in contralateral upper limb (UL) activity. Motor responses are also elicited in the ipsilateral UL, though controversy surrounds the significance of these effects. Evidence suggests that ipsilateral muscle activity is more common following the stimulation of the supplementary motor area (SMA) and dorsal premotor area (PMd), compared to the primary motor cortex (M1), but none of these studies compared effects from all three areas in the same subjects. This has limited our understanding of how these three cortical motor areas influence ipsilateral UL muscle activity. The purpose of this study was to determine the contribution of each of three cortical areas to the production of ipsilateral and contralateral UL. To maximize sensitivity and allow comparison of the effects across cortical areas, we applied the same stimulation parameters (36 pulse stimulus train at 330 Hz) to M1, SMA, and PMd in three adult M. fascicularis and recorded electromyographic (EMG) activity from muscles in the trunk and both ULs. Of all muscle responses identified, 24 % were ipsilateral to the stimulation, mostly in proximal muscles. The highest percentage of ipsilateral responses occurred following SMA stimulation. We also observed that PMd stimulation elicited more suppression responses compared with stimulation of M1 and SMA. The results indicate that ipsilateral motor areas provide a significant contribution to cortical activation of the trunk and proximal UL muscles. These understudied pathways may represent a functional substrate for future strategies to shape UL recovery following injury or stroke.