Suppression of the non-dominant motor cortex during bimanual symmetric finger movement: A functional magnetic resonance imaging study

Event-related theta synchronization over sensorimotor areas differs between younger and older adults and is related to bimanual motor control

When engaged in dynamic or continuous movements, action initiation involves modifying an ongoing motor program rather than initiating it from rest. Event-related theta synchronization over sensorimotor areas is a neurophysiological marker for modifying motor programs. We used electroencephalography (EEG) to examine how task complexity and age affect event-related synchronization (ERS) in the theta band during a dynamic bimanual, visuomotor pinch force task. Older (mean age = 68) and younger (mean age = 26) participants performed symmetric (SYM) and asymmetric (ASYM) bimanual pinch force adjustments. Trials began with a visually cued contraction from a baseline force to a novel target force (P1). Force had to be maintained at the target until a visually cued return to the familiar baseline (P2). Older adults reacted slower across task conditions, and their accuracy decreased more when shifting from the SYM to the ASYM condition. Older adults also displayed lower theta ERS across conditions. Additionally, older adults were not able to modulate theta expression based on whether a force change was initiated to a novel target or back to baseline. Younger adults showed significantly stronger theta ERS after P1-cues compared to P2-cues, while the theta response to P1 and P2 cues was not different in older adults. Older adults also showed stronger lateralization, displaying higher theta ERS over the dominant motor cortex. Finally, event-related theta synchronization appeared to be behaviorally relevant across groups and correlated with task performance. Together, the results show that theta ERS over sensorimotor areas is a strong, age-sensitive marker of dynamic pinch force adjustments showing an age-related reduction in specificity with reduced context-dependent modulations and more imbalanced bimanual activation.

A 12-week in-phase bilateral upper limb exercise protocol promoted neuroplastic and clinical changes in people with relapsing remitting multiple sclerosis: A registered report randomized single-case concurrent multiple baseline study

INTRODUCTION

Relapsing-Remitting Multiple Sclerosis manifests various motor symptoms including impairments in corticospinal tract integrity, whose symptoms can be assessed using transcranial magnetic stimulation. Several factors, such as exercise and interlimb coordination, can influence the plastic changes in corticospinal tract. Previous work in healthy and chronic stroke survivors showed that the greatest improvement in corticospinal plasticity occurred during in-phase bilateral exercises of the upper limbs. Altered corticospinal plasticity due to bilateral lesions in the central nervous system is common after Multiple Sclerosis, yet the effect of in-phase bilateral exercise on the bilateral corticospinal plasticity in this cohort remains unclear. Our aim was to investigate the effects of in-phase bilateral exercises on central motor conduction time, motor evoked potential amplitude and latency, motor threshold and clinical measures in people with Relapsing-Remitting Multiple Sclerosis.

METHODS

Five people were randomized and recruited in this single case concurrent multiple baseline design study. The intervention protocol lasted for 12 consecutive weeks (30-60 minutes /session x 3 sessions / week) and included in-phase bilateral upper limb movements, adapted to different sports activities and to functional motor training. To define the functional relation between the intervention and the results, we conducted a visual analysis. If a potential sizeable effect was observed, we subsequently performed a statistical analysis.

RESULTS

Results demonstrated bilateral reduction of the motor threshold alongside with improvement of all clinical measures, but not in any other corticospinal plasticity measures.

CONCLUSION

Our preliminary findings suggest that in-phase bilateral exercise affects motor threshold in people with Relapsing-Remitting Multiple Sclerosis. Therefore, this measure could potentially serve as a proxy for detecting corticospinal plasticity in this cohort. However, future studies with larger sample sizes should validate and potentially establish the effect of in-phase bilateral exercise on the corticospinal plasticity and clinical measures in this cohort.

TRIAL REGISTRATION

Clinical trial registration: ClinicalTrials.gov NCT05367947.

Advanced Force Coordination of Lower Extremities During Visuomotor Control Task in Soccer Players

Purpose: This study is aimed to determine specific bilateral lower extremity motor performances and coordination patterns in soccer players with healthy controls using the bilateral force control paradigm. We hypothesized that soccer players would show more advanced bilateral force control performances than untrained controls. Methods: Participants were 13 university soccer players and 13 healthy controls. Each group performed bilateral ankle dorsiflexion force control tasks across two vision conditions (i.e., vision and no-vision) and two targeted force levels (i.e., 10% and 40% maximum voluntary contraction). We calculated force accuracy, variability, and symmetry to assess force control performances. To estimate bilateral force coordination, we calculated Pearson's correlation coefficients between feet-within a single trial and considered uncontrolled manifold variables across multiple trials. In the no-vision condition, we performed secondary analyses for initial force control patters after removal of visual feedback. Results: There were no significant group differences in bilateral force accuracy and variability but, compared to the control group, soccer players showed higher force symmetry between left and right ankle dorsiflexion forces. For force coordination between feet, soccer players revealed more negative values of the correlation coefficient and greater good variability from the uncontrolled manifold analysis than those for the control group. The secondary analysis revealed no significant group differences in the time until force drift and amount of force adjustments. Conclusions: Soccer players have more compensatory and flexible interlimb force coordination strategies between feet.

Cortical activity in patients with high-functioning ischemic stroke during the Purdue Pegboard Test: insights into bimanual coordinated fine motor skills with functional near-infrared spectroscopy

After stroke, even high-functioning individuals may experience compromised bimanual coordination and fine motor dexterity, leading to reduced functional independence. Bilateral arm training has been proposed as a promising intervention to address these deficits. However, the neural basis of the impairment of functional fine motor skills and their relationship to bimanual coordination performance in stroke patients remains unclear, limiting the development of more targeted interventions. To address this gap, our study employed functional near-infrared spectroscopy to investigate cortical responses in patients after stroke as they perform functional tasks that engage fine motor control and coordination. Twenty-four high-functioning patients with ischemic stroke (7 women, 17 men; mean age 64.75 ± 10.84 years) participated in this cross-sectional observational study and completed four subtasks from the Purdue Pegboard Test, which measures unimanual and bimanual finger and hand dexterity. We found significant bilateral activation of the sensorimotor cortices during all Purdue Pegboard Test subtasks, with bimanual tasks inducing higher cortical activation than the assembly subtask. Importantly, patients with better bimanual coordination exhibited lower cortical activation during the other three Purdue Pegboard Test subtasks. Notably, the observed neural response patterns varied depending on the specific subtask. In the unaffected hand task, the differences were primarily observed in the ipsilesional hemisphere. In contrast, the bilateral sensorimotor cortices and the contralesional hemisphere played a more prominent role in the bimanual task and assembly task, respectively. While significant correlations were found between cortical activation and unimanual tasks, no significant correlations were observed with bimanual tasks. This study provides insights into the neural basis of bimanual coordination and fine motor skills in high-functioning patients after stroke, highlighting task-dependent neural responses. The findings also suggest that patients who exhibit better bimanual performance demonstrate more efficient cortical activation. Therefore, incorporating bilateral arm training in post-stroke rehabilitation is important for better outcomes. The combination of functional near-infrared spectroscopy with functional motor paradigms is valuable for assessing skills and developing targeted interventions in stroke rehabilitation.

The impact of lesion side on bilateral upper limb coordination after stroke

BACKGROUND

A stroke frequently results in impaired performance of activities of daily life. Many of these are highly dependent on effective coordination between the two arms. In the context of bimanual movements, cyclic rhythmical bilateral arm coordination patterns can be classified into two fundamental modes: in-phase (bilateral homologous muscles contract simultaneously) and anti-phase (bilateral muscles contract alternately) movements. We aimed to investigate how patients with left (LHS) and right (RHS) hemispheric stroke are differentially affected in both individual-limb control and inter-limb coordination during bilateral movements.

METHODS

We used kinematic measurements to assess bilateral coordination abilities of 18 chronic hemiparetic stroke patients (9 LHS; 9 RHS) and 18 age- and sex-matched controls. Using KINARM upper-limb exoskeleton system, we examined individual-limb control by quantifying trajectory variability in each hand and inter-limb coordination by computing the phase synchronization between hands during anti- and in-phase movements.

RESULTS

RHS patients exhibited greater impairment in individual- and inter-limb control during anti-phase movements, whilst LHS patients showed greater impairment in individual-limb control during in-phase movements alone. However, LHS patients further showed a swap in hand dominance during in-phase movements.

CONCLUSIONS

The current study used individual-limb and inter-limb kinematic profiles and showed that bilateral movements are differently impaired in patients with left vs. right hemispheric strokes. Our results demonstrate that both fundamental bilateral coordination modes are differently controlled in both hemispheres using a lesion model approach. From a clinical perspective, we suggest that lesion side should be taken into account for more individually targeted bilateral coordination training strategies.

TRIAL REGISTRATION

the current experiment is not a health care intervention study.

Neuromuscular Fatigue in Unimanual Handgrip Does Not Completely Affect Simultaneous Bimanual Handgrip

Simultaneous bimanual movements are not merely the sum of two unimanual movements. Here, we considered the unimanual/bimanual motor system as comprising three components: unimanual-specific, bimanual-specific, and overlapping (mobilized during both unimanual and bimanual movements). If the force-generating system controlling the same limb differs between unimanual and bimanual movements, unimanual exercise would be expected to fatigue the unimanual-specific and overlapping parts in the force-generating system but not the bimanual-specific part. Therefore, we predicted that the decrease in bimanual force generation induced by unimanual neuromuscular fatigue would be smaller than the decrease in unimanual force generation. Sixteen healthy right-handed adults performed unimanual and bimanual maximal handgrip measurements before and after a submaximal fatiguing handgrip task. In the fatigue task, participants were instructed to maintain unimanual handgrip force at 50% of their maximal handgrip force until the time to task failure. Each participant performed this task in a left-hand fatigue (LF) condition and a right-hand fatigue (RF) condition, in a random order. Although the degree of neuromuscular fatigue was comparable in both conditions, as expected, the decrease in bimanual right handgrip force was significantly smaller than those during unimanual right performance in the RF condition, but not in the LF condition. These results indicate that for the right-hand, neuromuscular fatigue in unimanual handgrip does not completely affect simultaneous bimanual handgrip. Regarding the underlying mechanisms, we propose that although neuromuscular fatigue caused by unimanual handgrip reduces the motor output of unimanual-specific and overlapping parts in the force-generating system, when simultaneous bimanual handgrip is performed, the overlapping part (which is partially fatigued) and the bimanual-specific part (which is not yet fatigued) generate motor output, thus decreasing the force reduction.

Alpha and beta neural oscillations differentially reflect age-related differences in bilateral coordination

Bilateral in-phase (IP) and anti-phase (AP) movements represent two fundamental modes of bilateral coordination that are essential for daily living. Although previous studies have shown that aging is behaviorally associated with decline in bilateral coordination, especially in AP movements, the underlying neural mechanisms remain unclear. Here, we use kinematic measurements and electroencephalography to compare motor performance of young and older adults executing bilateral IP and AP hand movements. On the behavioral level, inter-limb synchronization was reduced during AP movements compared to IP and this reduction was stronger in the older adults. On the neural level, we found interactions between group and condition for task-related power change in different frequency bands. The interaction was driven by smaller alpha power decreases over the non-dominant cortical motor area in young adults during IP movements and larger beta power decreases over the midline region in older adults during AP movements. In addition, the decrease in inter-limb synchronization during AP movements was predicted by stronger directional connectivity in the beta-band: an effect more pronounced in older adults. Our results therefore show that age-related differences in the two bilateral coordination modes are reflected on the neural level by differences in alpha and beta oscillatory power as well as interhemispheric directional connectivity.

Asymmetric transcallosal conduction delay leads to finer bimanual coordination

It has been theorized that hemispheric dominance and more segregated information processing have evolved to overcome long conduction delays through the corpus callosum (transcallosal conduction delay - TCD) but that this may still impact behavioral performance, mostly in tasks requiring high timing accuracy. Nevertheless, a thorough understanding of the temporal features of interhemispheric communication is lacking. Here, we aimed to assess the relationship between TCD and behavioral performance with a noninvasive directional cortical measure of TCD obtained from transcranial magnetic stimulation (TMS)-evoked potentials (TEPs) in the motor system. Twenty-one healthy right-handed subjects were tested. TEPs were recorded during an ipsilateral silent period (iSP) paradigm and integrated with diffusion tensor imaging (DTI) and an in-phase bimanual thumb-opposition task. Linear mixed models were applied to test relationships between measures. We found TEP indexes of transcallosal communication at ∼15 ms both after primary motor cortex stimulation (M1-P15) and after dorsal premotor cortex stimulation (dPMC-P15). Both M1-and dPMC-P15 were predicted by mean diffusivity in the callosal body. Moreover, M1-P15 was positively related to iSP. Importantly, M1-P15 latency was linked to bimanual coordination with direction-dependent effects, so that asymmetric TCD was the best predictor of bimanual coordination. Our findings support the idea that transcallosal timing in signal transmission is essential for interhemispheric communication and can impact the final behavioral outcome. However, they challenge the view that a short conduction delay is always beneficial. Rather, they suggest that the effect of the conduction delay may depend on the direction of information flow.

Attention-dependent switching between intrinsic-muscle and extrinsic-visual coordinates during bimanual movements

Inter-limb coordination is achieved through multiple levels of motor control based on intrinsic-muscle and extrinsic-visual coordinates. Online visual feedback affects which of these coordinates is dominant, and visual perception is involved in the switching of motor coordination across the two hands; however, it remains unclear whether there is any role for attention in inter-limb coordination. Therefore, we evaluated the effects of attention on the dominance of intrinsic-muscle and extrinsic-visual coordinates by investigating inter-limb interference in the right or left hand during bimanual reaching movements, as induced by visual perturbations. We first showed an effect of differences in online visual feedback on bimanual coordination (Experiment 1). We then revealed that attention to visual cursors that directly affected the hand movement led to the dominance of the intrinsic-muscle coordinates, which synchronized homologous muscle activities. In contrast, attention to an integrated visual object controlled by bilateral hand movements was associated with a preference for extrinsic-visual coordinates to synchronize bilateral movement directions (Experiment 2). Thus, attention-dependent switching between intrinsic-muscle and extrinsic-visual coordinates was observed during bimanual movements; extrinsic-visual coordinates may enable goal-directed bimanual movements at least for particular task requirements.

Drawing lines and circles in Parkinson's Disease: The lateralized symptoms interfere with the movements of the unaffected hand

INTRODUCTION

Evidence about altered bimanual coordination has been reported in Parkinson's Disease. However, no previous study has explored such an alteration quantifying the interference effect that the trajectory of each hand might impose on the other one. Thus, in the present research, we applied the traditional Circles-Lines Coupling Task, which allowed assessing the motor coordination of the two hands, in the context of Parkinson's Disease.

METHODS

Thirty-six individuals affected by Parkinson's Disease were consecutively recruited and assigned to two groups according to their symptoms' lateralization. Moreover, eighteen age-matched healthy controls participated in the study. We capitalized on the Circles-Lines Coupling Task, in which the performance during incongruent movements (drawing lines with one hand and circles with the other hand) was compared with the performance during congruent movements (drawing lines with both hands). A bimanual coupling index was computed to compare the interference effect of each hand on the other one.

RESULTS

In healthy controls, the bimanual coupling index did not differ between the two hands. Crucially, in both groups of individuals affected by Parkinson's Disease, the less affected hand showed a significantly higher bimanual coupling index, due to the abnormal interference exerted by the most affected one, than vice versa.

CONCLUSIONS

Our results highlighted an altered spatial bimanual coupling in Parkinson's disease, depending on the symptoms' lateralization. We offered different explanations of our results according to the theoretical frameworks about the mechanisms subserving bimanual coordination.

The difference in hemodynamic responses between dominant and non-dominant hands during muscle contraction and relaxation: An fNIRS study

The present study used functional near-infrared spectroscopy (fNIRS), and investigated the differences in neural activation of ipsi- or contralateral hemispheres between right dominant and left non-dominant hands among right-handed subjects using consecutive motor tasks with muscle contraction and relaxation. The subjects performed tasks under four conditions: (1) right hand up (R-Up), (2) left hand up (L-Up), (3) right hand down (R-Down), and (4) left hand down (L-Down). The peak amplitude of oxy-Hb was significantly larger at the contralateral than ipsilateral hemisphere in the premotor area (PM) under the R-Up condition, and no significant differences were observed between contra- and ipsilateral hemispheres under the L-Up condition. In addition, the peak amplitude was more negative at the contra- than ipsilateral hemisphere in the PM under the R-Down condition, while the peak amplitude was significantly more negative at the ipsi- than contralateral hemisphere in the PM under the L-Down condition. These results suggest that the PM of the left hemisphere among right-handed subjects plays an important role in muscle contraction and relaxation with force control.

Bilateral Contralaterally Controlled Functional Electrical Stimulation Reveals New Insights Into the Interhemispheric Competition Model in Chronic Stroke

Background. Upper-limb chronic stroke hemiplegia was once thought to persist because of disproportionate amounts of inhibition imposed from the contralesional on the ipsilesional hemisphere. Thus, one rehabilitation strategy involves discouraging engagement of the contralesional hemisphere by only engaging the impaired upper limb with intensive unilateral activities. However, this premise has recently been debated and has been shown to be task specific and/or apply only to a subset of the stroke population. Bilateral rehabilitation, conversely, engages both hemispheres and has been shown to benefit motor recovery. To determine what neurophysiological strategies bilateral therapies may engage, we compared the effects of a bilateral and unilateral based therapy using transcranial magnetic stimulation. Methods. We adopted a peripheral electrical stimulation paradigm where participants received 1 session of bilateral contralaterally controlled functional electrical stimulation (CCFES) and 1 session of unilateral cyclic neuromuscular electrical stimulation (cNMES) in a repeated-measures design. In all, 15 chronic stroke participants with a wide range of motor impairments (upper extremity Fugl-Meyer score: 15 [severe] to 63 [mild]) underwent single 1-hour sessions of CCFES and cNMES. We measured whether CCFES and cNMES produced different effects on interhemispheric inhibition (IHI) to the ipsilesional hemisphere, ipsilesional corticospinal output, and ipsilateral corticospinal output originating from the contralesional hemisphere. Results. CCFES reduced IHI and maintained ipsilesional output when compared with cNMES. We found no effect on ipsilateral output for either condition. Finally, the less-impaired participants demonstrated a greater increase in ipsilesional output following CCFES. Conclusions. Our results suggest that bilateral therapies are capable of alleviating inhibition on the ipsilesional hemisphere and enhancing output to the paretic limb.

Negative BOLD responses during hand and foot movements: An fMRI study

The present study employed functional magnetic resonance imaging (fMRI) to examine the characteristics of negative blood oxygen level-dependent (Negative BOLD) signals during motor execution. Subjects repeated extension and flexion of one of the following: the right hand, left hand, right ankle, or left ankle. Negative BOLD responses during hand movements were observed in the ipsilateral hemisphere of the hand primary sensorimotor area (SMI), medial frontal gyrus (MeFG), middle frontal gyrus (MFG), and superior frontal gyrus (SFG). Negative BOLD responses during foot movements were also noted in the bilateral hand SMI, MeFG, MFG, SFG, inferior frontal gyrus, middle temporal gyrus, parahippocampal gyrus, anterior cingulate cortex, cingulate gyrus (CG), fusiform gyrus, and precuneus. A conjunction analysis showed that portions of the MeFG and CG involving similar regions to those of the default mode network were commonly deactivated during voluntary movements of the right/left hand or foot. The present results suggest that three mechanisms are involved in the Negative BOLD responses observed during voluntary movements: (1) transcallosal inhibition from the contralateral to ipsilateral hemisphere in the SMI, (2) the deactivated neural network with several brain regions, and (3) the default mode network in the MeFG and CG.

Shared right-hemispheric representations of sensorimotor goals in dynamic task environments

Functional behaviour affords that we form goals to integrate sensory information about the world around us with suitable motor actions, such as when we plan to grab an object with a hand. However, much research has tested grasping in static scenarios where goals are pursued with repetitive movements, whereas dynamic contexts require goals to be pursued even when changes in the environment require a change in the actions to attain them. To study grasp goals in dynamic environments here, we employed a task where the goal remained the same but the execution of the movement changed; we primed participants to grasp objects either with their right or left hand, and occasionally they had to switch to grasping with both. Switch costs should be minimal if grasp goal representations were used continuously, for example, within the left dominant hemisphere. But remapped or re-computed goal representations should delay movements. We found that switching from right-hand grasping to bimanual grasping delayed reaction times but switching from left-hand grasping to bimanual grasping did not. Further, control experiments showed that the lateralized switch costs were not caused by asymmetric inhibition between hemispheres or switches between usual and unusual tasks. Our results show that the left hemisphere does not serve a general role of sensorimotor grasp goal representation. Instead, sensorimotor grasp goals appear to be represented at intermediate levels of abstraction, downstream from cognitive task representations, yet upstream from the control of the grasping effectors.

Impact of Handedness Consistency on Bimanual and Unimanual Continuous Movements

Bimanual coordination is an essential human function requiring efficient interhemispheric communication to produce coordinated movements. Previous research suggests a "bimanual advantage" phenomenon, where completing synchronized bimanual tasks results in less variability than unimanual tasks. Additionally, of hand dominance has been shown to influence coordinated performance. The present study examined the bimanual advantage in individuals with consistent and inconsistent handedness. It was predicted that participants with consistent handedness would not display a bimanual advantage unlike those with inconsistent handedness. Fifty-six young adults completed a finger-tapping paradigm in five conditions: unimanual tapping with either left or right hand, in-phase bimanual tapping, and out-of phase bimanual tapping led by either left or right hand. Results were not consistent with the hypothesis that participants with consistent handedness displayed the "bimanual advantage". However, the "bimanual advantage" was not evident for the inconsistent handers when the temporal consistency was measured with either the left or right hand only. Overall, the "bimanual advantage" may be dependent upon consistency of hand preference, as well as the direction of hand dominance.

Manual action verbs modulate the grip force of each hand in unimanual or symmetrical bimanual tasks

Manual action verbs modulate the right-hand grip force in right-handed subjects. However, to our knowledge, no studies demonstrate the ability to accomplish this modulation during bimanual tasks nor describe their effect on left-hand behavior in unimanual and bimanual tasks. Using load cells and word playlists, we evaluated the occurrence of grip force modulation by manual action verbs in unimanual and symmetrical bimanual tasks across the three auditory processing phases. We found a significant grip force increase for all conditions compared to baseline, indicating the occurrence of modulation. When compared to each other, the grip force variation from baseline for the three phases of both hands in the symmetrical bimanual task was not different from the right-hand in the unimanual task. The left-hand grip force showed a lower amplitude for auditory phases 1 and 2 when compared to the other conditions. The right-hand grip force modulation became significant from baseline at 220 ms after the word onset in the unimanual task. This moment occurred earlier for both hands in bimanual task (160 ms for the right-hand and 180 for the left-hand). It occurred later for the left-hand in unimanual task (320 ms). We discuss the hypothesis that Broca's area and Broca's homologue area likely control the left-hand modulation in a unilateral or a bilateral fashion. These results provide new evidence for understanding the linguistic function processing in both hemispheres.

Reduced striato-cortical and inhibitory transcallosal connectivity in the motor circuit of Huntington's disease patients

Huntington's disease (HD) is a neurodegenerative disorder which is primarily associated with striatal degeneration. However, the alterations in connectivity of this structure in HD have been underinvestigated. In this study, we analyzed the functional and structural connectivity of the left putamen, while participants performed a finger-tapping task. Using fMRI and DW-MRI, 30 HD gene expansion carriers (HDGEC) and 29 healthy participants were scanned. Psychophysiological interaction analysis and DTI-based tractography were employed to examine functional and structural connectivity, respectively. Manifest HDGEC exhibited a reduced functional connectivity of the left putamen with the left and the right primary sensorimotor areas (SM1). Based on this result, the inhibitory functional connectivity between the left SM1 and the right SM1 was explored, appearing to be also decreased. In addition, the tract connecting these areas (motor corpus callosum), and the tract connecting the left putamen with the left SM1 appeared disrupted in HDGEC compared to controls. Significant correlations were found between measures of functional and structural connectivity of the motor corpus callosum, showing a coupling of both types of alterations in this tract. The observed reduction of functional and structural connectivity was associated with worse motor scores, which highlights the clinical relevance of these results. Hum Brain Mapp 39:54-71, 2018. © 2017 Wiley Periodicals, Inc.

Corticospinal Modulations during Bimanual Movement with Different Relative Phases

The purpose of this study was to investigate corticospinal modulation of bimanual (BM) movement with different relative phases (RPs). The participants rhythmically abducted and adducted the right index finger (unimanual (UM) movement) or both index fingers (BM movement) with a cyclic duration of 1 s. The RP of BM movement, defined as the time difference between one hand movement and the other hand movement, was 0°, 90°, or 180°. Motor evoked potentials (MEPs) in the right flexor dorsal interosseous muscle elicited by transcranial magnetic stimulation (TMS) were obtained during UM or BM movement. Corticospinal excitability in the first dorsal interosseous muscle during BM movement with 90° RP was higher than that during UM movement or BM movement with 0° or 180° RP. The correlation between muscle activity level and corticospinal excitability during BM movement with 90° RP was smaller than that during UM movement or BM movement with 0° or 180° RP. The higher corticospinal excitability during BM movement with 90° RP may be caused by the greater effort expended to execute a difficult task, the involvement of interhemispheric interaction, a motor binding process, or task acquisition. The lower dependency of corticospinal excitability on the muscle activity level during BM movement with 90° RP may reflect the minor corticospinal contribution to BM movement with an RP that is not in the attractor state.

The curse of motor expertise: Use-dependent focal dystonia as a manifestation of maladaptive changes in body representation

Focal task-specific dystonia (FTSD) impairs not only motor dexterity, but also somatosensory perception involved in well-trained behavioral tasks. Occupations that carry a risk of developing FTSD include musician, writer, painter, surgeon, and golfer, which are characterized by repetitive and precise motor actions over a prolonged period. Behavioral studies have uncovered various undesirable effects of FTSD on sensorimotor functions, such as a loss of independent movement control, unintended muscular co-activation, awkward limb posture, and impairment of fine discrimination of tactile and proprioceptive sensations. Studies using neuroimaging and noninvasive brain stimulation techniques have related such sensorimotor malfunctions to maladaptive neuroplastic changes in the sensorimotor system, including the primary motor and somatosensory areas, premotor area, cerebellum, and basal ganglia. In this review, we summarize recent empirical findings regarding phenomenological and pathophysiological abnormalities associated with the development of FTSD. We particularly focused on maladaptive alterations of body representations underlying the degradation of fine motor control and somatosensory perception in FTSD patients.

Bimanual non-congruent actions in motor neglect syndrome: a combined behavioral/fMRI study

In Motor Neglect (MN) syndrome, a specific impairment in non-congruent bimanual movements has been described. In the present case-control study, we investigated the neuro-functional correlates of this behavioral deficit. Two right-brain-damaged (RBD) patients, one with (MN+) and one without (MN−) MN, were evaluated by means of functional Magnetic Resonance Imaging (fMRI) in a bimanual Circles-Lines (CL) paradigm. Patients were requested to perform right-hand movements (lines-drawing) and, simultaneously, congruent (lines-drawing) or non-congruent (circles-drawing) left-hand movements. In the behavioral task, MN− patient showed a bimanual-coupling-effect, while MN+ patient did not. The fMRI study showed that in MN−, a fronto-parietal network, mainly involving the pre-supplementary motor area (pre-SMA) and the posterior parietal cortex (PPC), was significantly more active in non-congruent than in congruent conditions, as previously shown in healthy subjects. On the contrary, MN+ patient showed an opposite pattern of activation both in pre-SMA and in PPC. Within this fronto-parietal network, the pre-SMA is supposed to exert an inhibitory influence on the default coupling of homologous muscles, thus allowing the execution of non-congruent movements. In MN syndrome, the described abnormal pre-SMA activity supports the hypothesis that a failure to inhibit ipsilesional motor programs might determine a specific impairment of non-congruent movements.

Tailoring Brain Stimulation to the Nature of Rehabilitative Therapies in Stroke: A Conceptual Framework Based on their Unique Mechanisms of Recovery

Despite showing early promise, several recent clinical trials of noninvasive brain stimulation (NIBS) failed to augment rehabilitative outcomes of the paretic upper limb. This article addresses why pairing NIBS with unilateral approaches is weakly generalizable to patients in all ranges of impairments. The article also addresses whether alternate therapies are better suited for the more impaired patients, where they may be more feasible and offer neurophysiologic advantages not offered with unilateral therapies. The article concludes by providing insight on how to create NIBS paradigms that are tailored to distinctly augment the effects of therapies across patients with varying degrees of impairment.

Insights from the supplementary motor area syndrome in balancing movement initiation and inhibition

The supplementary motor area (SMA) syndrome is a characteristic neurosurgical syndrome that can occur after unilateral resection of the SMA. Clinical symptoms may vary from none to a global akinesia, predominantly on the contralateral side, with preserved muscle strength and mutism. A remarkable feature is that these symptoms completely resolve within weeks to months, leaving only a disturbance in alternating bimanual movements. In this review we give an overview of the old and new insights from the SMA syndrome and extrapolate these findings to seemingly unrelated diseases and symptoms such as Parkinson's disease (PD) and tics. Furthermore, we integrate findings from lesion, stimulation and functional imaging studies to provide insight in the motor function of the SMA.

Bimanual force variability and chronic stroke: asymmetrical hand control

The purpose of this study was to investigate force variability generated by both the paretic and non-paretic hands during bimanual force control. Nine chronic stroke individuals and nine age-matched individuals with no stroke history performed a force control task with both hands simultaneously. The task involved extending the wrist and fingers at 5%, 25%, and 50% of maximum voluntary contraction. Bimanual and unimanual force variability during bimanual force control was determined by calculating the coefficient of variation. Analyses revealed two main findings: (a) greater bimanual force variability in the stroke group than the control group and (b) increased force variability by the paretic hands during bimanual force control in comparison to the non-paretic hands at the 5% and 25% force production conditions. A primary conclusion is that post stroke bimanual force variability is asymmetrical between hands.

Bimanual coupling paradigm as an effective tool to investigate productive behaviors in motor and body awareness impairments

When humans move simultaneously both hands strong coupling effects arise and neither of the two hands is able to perform independent actions. It has been suggested that such motor constraints are tightly linked to action representation rather than to movement execution. Hence, bimanual tasks can represent an ideal experimental tool to investigate internal motor representations in those neurological conditions in which the movement of one hand is impaired. Indeed, any effect on the “moving” (healthy) hand would be caused by the constraints imposed by the ongoing motor program of the ‘impaired’ hand. Here, we review recent studies that successfully utilized the above-mentioned paradigms to investigate some types of productive motor behaviors in stroke patients. Specifically, bimanual tasks have been employed in left hemiplegic patients who report illusory movements of their contralesional limbs (anosognosia for hemiplegia). They have also been administered to patients affected by a specific monothematic delusion of body ownership, namely the belief that another person’s arm and his/her voluntary action belong to them. In summary, the reviewed studies show that bimanual tasks are a simple and valuable experimental method apt to reveal information about the motor programs of a paralyzed limb. Therefore, it can be used to objectively examine the cognitive processes underpinning motor programming in patients with different delusions of motor behavior. Additionally, it also sheds light on the mechanisms subserving bimanual coordination in the intact brain suggesting that action representation might be sufficient to produce these effects.

Drawing lines while imagining circles: Neural basis of the bimanual coupling effect during motor execution and motor imagery

When people simultaneously draw lines with one hand and circles with the other hand, both trajectories tend to assume an oval shape, showing that hand motor programs interact (the so-called "bimanual coupling effect"). The aim of the present study was to investigate how motor parameters (drawing trajectories) and the related brain activity vary during bimanual movements both in real execution and in motor imagery tasks. In the 'Real' modality, subjects performed right hand movements (lines) and, simultaneously, Congruent (lines) or Non-congruent (circles) left hand movements. In the 'Imagery' modality, subjects performed only right hand movements (lines) and, simultaneously, imagined Congruent (lines) or Non-congruent (circles) left hand movements. Behavioral results showed a similar interference of both the real and the imagined circles on the actually executed lines, suggesting that the coupling effect also pertains to motor imagery. Neuroimaging results showed that a prefrontal-parietal network, mostly involving the pre-Supplementary Motor Area (pre-SMA) and the posterior parietal cortex (PPC), was significantly more active in Non-congruent than in Congruent conditions, irrespective of task (Real or Imagery). The data also confirmed specific roles of the right superior parietal lobe (SPL) in mediating spatial interference, and of the left PPC in motor imagery. Collectively, these findings suggest that real and imagined Non-congruent movements activate common circuits related to the intentional and predictive operation generating bimanual coupling, in which the pre-SMA and the PPC play a crucial role.

Complexity of motor sequences and cortical reorganization in Parkinson's disease: a functional MRI study

Motor impairment is the most relevant clinical feature in Parkinson's disease (PD). Functional imaging studies on motor impairment in PD have revealed changes in the cortical motor circuits, with particular involvement of the fronto-striatal network. The aim of this study was to assess brain activations during the performance of three different motor exercises, characterized by progressive complexity, using a functional fMRI multiple block paradigm, in PD patients and matched control subjects. Unlike from single-task comparisons, multi-task comparisons between similar exercises allowed to analyse brain areas involved in motor complexity planning and execution. Our results showed that in the single-task comparisons the involvement of primary and secondary motor areas was observed, consistent with previous findings based on similar paradigms. Most notably, in the multi-task comparisons a greater activation of supplementary motor area and posterior parietal cortex in PD patients, compared with controls, was observed. Furthermore, PD patients, compared with controls, had a lower activation of the basal ganglia and limbic structures, presumably leading to the impairment in the higher levels of motor control, including complexity planning and execution. The findings suggest that in PD patients occur both compensatory mechanisms and loss of efficiency and provide further insight into the pathophysiological role of distinct cortical and subcortical areas in motor dysfunction.

Effects of finger tapping frequency on regional homogeneity of sensorimotor cortex

Resting-state functional magnetic resonance imaging (RS-fMRI) has been widely used to investigate temporally correlated fluctuations between distributed brain areas, as well as to characterize local synchronization of low frequency (<0.1 Hz) spontaneous fMRI signal. Regional homogeneity (ReHo) was proposed as a voxel-wise measure of the synchronization of the timecourses of neighboring voxels and has been used in many studies of brain disorders. However, the interpretation of ReHo remains challenging because the effect of high frequency task on ReHo is still not clear. In order to investigate the effect of a high-frequency task on the modulation of local synchronization of resting-state activity, we employed three right-finger movement scanning sessions: slow-event related (‘Slow’), fast-event related (‘Fast’), and continuous finger pressure (‘Tonic’), from 21 healthy participants and compared the ReHo of the three task states with that of resting-state (‘Rest’). In the contralateral sensorimotor cortex, ‘Slow’ task state showed greater ReHo than ‘Rest’ in low frequency band (0–0.08Hz) fMRI signal, but lower ReHo in high frequency band (0.08–1.67 Hz); ‘Fast’ task state showed lower ReHo than ‘Rest’ in both the low and high frequency band; ‘Tonic’ state did not show any significant difference compared to ‘Rest’. The results in the contralateral sensorimotor cortex suggest that local synchronization of BOLD signal varies with different finger tapping speed. In the ipsilateral sensorimotor cortex, all the three task states had lower ReHo than the ‘Rest’ state both in the low and high frequency, suggesting a similar effect of fast and slow finger tapping frequencies on local synchronization of BOLD signal in the ipsilateral motor cortex.

Motor control and neural plasticity through interhemispheric interactions

The corpus callosum, which is the largest white matter structure in the human brain, connects the 2 cerebral hemispheres. It plays a crucial role in maintaining the independent processing of the hemispheres and in integrating information between both hemispheres. The functional integrity of interhemispheric interactions can be tested electrophysiologically in humans by using transcranial magnetic stimulation, electroencephalography, and functional magnetic resonance imaging. As a brain structural imaging, diffusion tensor imaging has revealed the microstructural connectivity underlying interhemispheric interactions. Sex, age, and motor training in addition to the size of the corpus callosum influence interhemispheric interactions. Several neurological disorders change hemispheric asymmetry directly by impairing the corpus callosum. Moreover, stroke lesions and unilateral peripheral impairments such as amputation alter interhemispheric interactions indirectly. Noninvasive brain stimulation changes the interhemispheric interactions between both motor cortices. Recently, these brain stimulation techniques were applied in the clinical rehabilitation of patients with stroke by ameliorating the deteriorated modulation of interhemispheric interactions. Here, we review the interhemispheric interactions and mechanisms underlying the pathogenesis of these interactions and propose rehabilitative approaches for appropriate cortical reorganization.

Spatiotemporal re-organization of large-scale neural assemblies underlies bimanual coordination

Bimanual coordination engages a distributed network of brain areas, the spatiotemporal organization of which has given rise to intense debates. Do bimanual movements require information processing in the same set of brain areas that are engaged by movements of the individual components (left and right hands)? Or is it necessary that other brain areas are recruited to help in the act of coordination? These two possibilities are often considered as mutually exclusive, with studies yielding support for one or the other depending on techniques and hypotheses. However, as yet there is no account of how the two views may work together dynamically. Using the method of Mode-Level Cognitive Subtraction (MLCS) on high density EEG recorded during unimanual and bimanual movements, we expose spatiotemporal reorganization of large-scale cortical networks during stable inphase and antiphase coordination and transitions between them. During execution of stable bimanual coordination patterns, neural dynamics were dominated by temporal modulation of unimanual networks. At instability and transition, there was evidence for recruitment of additional areas. Our study provides a framework to quantify large-scale network mechanisms underlying complex cognitive tasks often studied with macroscopic neurophysiological recordings.

Coordination of uncoupled bimanual movements by strictly timed interhemispheric connectivity

Independent use of both hands is characteristic of human action in daily life. By nature, however, in-phase bimanual movements, for example clapping, are easier to accomplish than anti-phase movements, for example playing the piano. It is commonly agreed that interhemispheric interactions play a central role in the coordination of bimanual movements. However, the spatial, temporal, and physiological properties of the interhemispheric signals that coordinate different modes of bimanual movements are still not completely understood. More precisely, do individual interhemispheric connectivity parameters have behavioral relevance for bimanual rapid anti-phase coordination? To address this question, we measured movement-related interhemispheric interactions, i.e., inhibition and facilitation, and correlated them with the performance during bimanual coordination. We found that movement-related facilitation from right premotor to left primary motor cortex (rPMd-lM1) predicted performance in anti-phase bimanual movements. It is of note that only fast facilitation during the preparatory period of a movement was associated with success in anti-phase movements. Modulation of right to left primary motor interaction (rM1-lM1) was not related to anti-phase but predicted bimanual in-phase and unimanual behavior. These data suggest that strictly timed modulation of interhemispheric rPMd-lM1 connectivity is essential for independent high-frequency use of both hands. The rM1-lM1 results indicate that adjustment of connectivity between homologous M1 may be important for the regulation of homologous muscle synergies.

Current trends in stroke rehabilitation. A review with focus on brain plasticity

Current understanding of brain plasticity has lead to new approaches in ischemic stroke rehabilitation. Stroke units that combine good medical and nursing care with task-oriented intense training in an environment that provides confidence, stimulation and motivation significantly improve outcome. Repetitive trans-cranial magnetic stimulation (rTMS), and trans-cranial direct current stimulation (tDCS) are applied in rehabilitation of motor function. The long-term effect, optimal way of stimulation and possibly efficacy in cognitive rehabilitation need evaluation. Methods based on multisensory integration of motor, cognitive, and perceptual processes including action observation, mental training, and virtual reality are being tested. Different approaches of intensive aphasia training are described. Recent data on intensive melodic intonation therapy indicate that even patients with very severe non-fluent aphasia can regain speech through homotopic white matter tract plasticity. Music therapy is applied in motor and cognitive rehabilitation. To avoid the confounding effect of spontaneous improvement, most trials are preformed ≥3 months post stroke. Randomized controlled trials starting earlier after strokes are needed. More attention should be given to stroke heterogeneity, cognitive rehabilitation, and social adjustment and to genetic differences, including the role of BDNF polymorphism in brain plasticity.

Limitations on coupling of bimanual movements caused by arm dominance: when the muscle homology principle fails

Studies of bimanual movements typically report interference between motions of the two arms and preference to perform mirror-symmetrical patterns. However, recent studies have demonstrated that the two arms differ in the ability to control interaction torque (INT). This predicts limitations in the capability to perform mirror-symmetrical movements. Here, two experiments were performed to test this prediction. The first experiment included bimanual symmetrical and asymmetrical circle drawing at two frequency levels. Unimanual circle drawing was also recorded. The increases in cycling frequency caused differences between the two arms in movement trajectories in both bimanual modes, although the differences were more pronounced in the asymmetrical compared with the symmetrical mode. Based on torque analysis, the differences were attributed to the nondominant arm's decreased capability to control INT. The intraarm differences during the symmetrical pattern of bimanual movements were similar (although more pronounced) to those during unimanual movements. This finding was verified in the second experiment for symmetrical bimanual oval drawing. Four oval orientations were used to provide variations in INT. Similar to the first experiment, increases in cycling frequency caused spontaneous deviations from perfect bimanual symmetry associated with inefficient INT control in the nondominant arm. This finding supports the limitations in performing mirror-symmetrical bimanual movements due to differences in joint control between the arms. Based on our results and previous research, we argue that bimanual interference occurs during specification of characteristics of required motion, whereas lower-level generation of muscle forces is independent between the arms. A hierarchical model of bimanual control is proposed.

Multiple interactions between hemispheres of the brain modulating coupling of bilateral movements

Interaction between motor areas of the right and left hemispheres of the brain is important for generating bilateral coordinated movements. We investigated how bilateral coupling, which results from the interhemispheric interaction, is modulated during coordinated movements. We tried to estimate coupling and stability of bilateral movements during continuous movements of the right and left index fingers. The experimental results show that bilateral coupling strengthens during symmetric movements and same directional movements. However, coordination stabilities depend on only symmetry. The results suggest that two or more interhemispheric interactions contribute to control the bilateral coordinated movements.

Functional Asymmetries Revealed in Visually Guided Saccades: An fMRI Study

Because eye movements are a fundamental tool for spatial exploration, we hypothesized that the neural bases of these movements in humans should be under right cerebral dominance, as already described for spatial attention. We used functional magnetic resonance imaging in 27 right-handed participants who alternated central fixation with either large or small visually guided saccades (VGS), equally performed in both directions. Hemispheric functional asymmetry was analyzed to identify whether brain regions showing VGS activation elicited hemispheric asymmetries. Hemispheric anatomical asymmetry was also estimated to assess its influence on the VGS functional lateralization. Right asymmetrical activations of a saccadic/attentional system were observed in the lateral frontal eye fields (FEF), the anterior part of the intraparietal sulcus (aIPS), the posterior third of the superior temporal sulcus (STS), the occipitotemporal junction (MT/V5 area), the middle occipital gyrus, and medially along the calcarine fissure (V1). The present rightward functional asymmetries were not related to differences in gray matter (GM) density/sulci positions between right and left hemispheres in the precentral, intraparietal, superior temporal, and extrastriate regions. Only V1 asymmetries were explained for almost 20% of the variance by a difference in the position of the right and left calcarine fissures. Left asymmetrical activations of a saccadic motor system were observed in the medial FEF and in the motor strip eye field along the Rolando sulcus. They were not explained by GM asymmetries. We suggest that the leftward saccadic motor asymmetry is part of a general dominance of the left motor cortex in right-handers, which must include an effect of sighting dominance. Our results demonstrate that, although bilateral by nature, the brain network involved in the execution of VGSs, irrespective of their direction, presented specific right and left asymmetries that were not related to anatomical differences in sulci positions.

Task complexity relates to activation of cortical motor areas during uni- and bimanual performance: a functional NIRS study

Hand motor tasks are frequently used to assess impaired motor function in neurology and neurorehabilitation. Assessments can be varied by means of hand laterality, i.e. unimanual or bimanual performance, as well as by means of task complexity, i.e. different degrees ranging from simple to complex sequence tasks. The resulting functional activation in human primary motor cortex (M1) has been studied intensively by traditional neuroimaging methods. Previous studies using functional near-infrared spectroscopy (fNIRS) investigated simple hand motor tasks. However, it is unknown whether fNIRS can also detect changes in response to increasing task complexity. Our hypothesis was to show that fNIRS could detect activation changes in relation to task complexity in uni- and bimanual tasks. Sixteen healthy right-handed subjects performed five finger-tapping tasks: unimanual left and right, simple and complex tasks as well as bimanual complex tasks. We found significant differences in oxy-hemoglobin (O(2)Hb) and deoxy-hemoglobin (HHb) concentration in the right hemisphere over M1. Largest O(2)Hb concentration changes were found during complex (0.351+/-0.051 micromol/l) and simple (0.275+/-0.054 micromol/l) right hand tasks followed by bimanual (0.249+/-0.047 micromol/l), complex (0.154+/-0.034 micromol/l) and simple (0.110+/-0.034 micromol/l) left hand tasks. Largest HHb concentration changes were found during bimanual (-0.138+/-0.006 micromol/l) tasks, followed by simple right hand (-0.12+/-0.016 micromol/l), complex left (-0.0875+/-0.007 micromol/l), complex right (-0.0863+/-0.005 micromol/l) and simple left (-0.0674+/-0.005 micromol/l) hand tasks. We report for the first time that fNIRS detects oxygenation changes in relation to task complexity during finger-tapping. The study aims to contribute to the establishment of fNIRS as a neuroimaging method to assess hand motor function in clinical settings where traditional neuroimaging methods cannot be applied.

Brain activation in multiple sclerosis: a BOLD fMRI study of the effects of fatiguing hand exercise

Background

Multiple sclerosis (MS) patients experience fatigue as a chronic symptom that decreases quality of life. Commonly, fatigue in MS patients is manifested as decreased motor function during or after physical activity and is associated with changes in brain metabolism.

Objective

To determine brain activation patterns in MS patients and healthy controls during a simple motor task before and after fatiguing hand-grip exercise.

Methods

Functional magnetic resonance imaging (fMRI) scans were conducted on 10 MS patients and 13 healthy controls during 4-finger flexion and extension in rested and fatigued states.

Results

Before the fatigue protocol, MS patients had greater activation in the contralateral primary motor cortex, insula, and cingulate gyrus than controls. Following fatiguing exercise, controls showed increased activation of precentral gyrus and insula while patients did not show any activation increases and actually decreased activity to the insula.

Conclusion

Results indicate that before fatiguing exercise, MS patients marshaled more brain activation compared to controls, which may represent functionally adaptive changes in response to demyelination. This increased activation may suggest that patients require more effort to perform even simple motor tasks, possibly because peripheral or central signals for fatigue are chronically enhanced. When fatigued further by muscle contraction, brain activation cannot be further increased.

Network activation during bimanual movements in humans

The coordination of movement between the upper limbs is a function highly distributed across the animal kingdom. How the central nervous system generates such bilateral, synchronous movements, and how this differs from the generation of unilateral movements, remain uncertain. Electrophysiologic and functional imaging studies support that the activity of many brain regions during bimanual and unimanual movement is quite similar. Thus, the same brain regions (and indeed the same neurons) respond similarly during unimanual and bimanual movements as measured by electrophysiological responses. How then are different motor behaviors generated? To address this question, we studied unimanual and bimanual movements using fMRI and constructed networks of activation using Structural Equation Modeling (SEM). Our results suggest that (1) the dominant hemisphere appears to initiate activity responsible for bimanual movement; (2) activation during bimanual movement does not reflect the sum of right and left unimanual activation; (3) production of unimanual movement involves a network that is distinct from, and not a mirror of, the network for contralateral unimanual movement; and (4) using SEM, it is possible to obtain robust group networks representative of a population and to identify individual networks which can be used to detect subtle differences both between subjects as well as within a single subject over time. In summary, these results highlight a differential role for the dominant and non-dominant hemispheres during bimanual movements, further elaborating the concept of handedness and dominance. This knowledge increases our understanding of cortical motor physiology in health and after neurological damage.

Asymmetric control mechanisms of bimanual coordination: an application of directed connectivity analysis to kinematic and functional MRI data

Mirror-symmetrical bimanual movement is more stable than parallel bimanual movement. This is well established at the kinematic level. We used functional MRI (fMRI) to evaluate the neural substrates of the stability of mirror-symmetrical bimanual movement. Right-handed participants (n=17) rotated disks with their index fingers bimanually, both in mirror-symmetrical and asymmetrical parallel modes. We applied the Akaike causality model to both kinematic and fMRI time-series data. We hypothesized that kinematic stability is represented by the extent of neural "cross-talk": as the fraction of signals that are common to controlling both hands increases, the stability also increases. The standard deviation of the phase difference for the mirror mode was significantly smaller than that for the parallel mode, confirming that the former was more stable. We used the noise-contribution ratio (NCR), which was computed using a multivariate autoregressive model with latent variables, as a direct measure of the cross-talk between both the two hands and the bilateral primary motor cortices (M1s). The mode-by-direction interaction of the NCR was significant in both the kinematic and fMRI data. Furthermore, in both sets of data, the NCR from the right hand (left M1) to the left (right M1) was more prominent than vice versa during the mirror-symmetrical mode, whereas no difference was observed during parallel movement or rest. The asymmetric interhemispheric interaction from the left M1 to the right M1 during symmetric bimanual movement might represent cortical-level cross-talk, which contributes to the stability of symmetric bimanual movements.