Intermanual coordination: from behavioural principles to neural-network interactions

Bimanual Coordination in Children with Bilateral Cerebral Palsy: A Cross-Sectional Study

AIM

To compare bimanual coordination in children with bilateral cerebral palsy (BCP) with that of children with typical development (TD) and correlate bimanual coordination with clinical measures of hand function.

METHODS

3-D kinematic data were collected from 14 children with BCP (mean age 13 years 1 month; range 7.3-17.2 years, 5 females) and 14 age-matched children with TD (mean age 13 years 1 month, range 7.0-16.0 years, 7 females) as they opened a drawer with one hand and activated a switch inside it with the other hand at self-paced and as-fast-as-possible speeds. Hand roles varied in each condition. Participants' hand function levels were classified using the Manual Ability Classification System. Unimanual dexterity and bimanual performance were evaluated using the Box and Blocks Test and Both Hands Assessment respectively.

RESULTS

Participants with BCP performed the bimanual task more slowly (p < 0.001) and sequentially, as evidenced by greater time differences between the two hands achieving the end goal (p = 0.01). Faster speeds, particularly when the less affected hand opened the drawer, facilitated time-related measures of bimanual coordination (p < 0.05). Bimanual coordination correlated with all clinical measures of hand function (p < 0.05).

CONCLUSION

For children with BCP, speed and hand used for each subcomponent of the task influence bimanual coordination. Better bimanual coordination is associated with less impairment of both hands.

Interhemispheric inhibition and gait adaptation associations in people with multiple sclerosis

BACKGROUND

Multiple sclerosis is a neurodegenerative disease that damages the myelin sheath within the central nervous system. Axonal demyelination, particularly in the corpus callosum, impacts communication between the brain's hemispheres in persons with multiple sclerosis (PwMS). Changes in interhemispheric communication may impair gait coordination which is modulated by communication across the corpus callosum to excite and inhibit specific muscle groups. To further evaluate the functional role of interhemispheric communication in gait and mobility, this study assessed the ipsilateral silent period (iSP), an indirect marker of interhemispheric inhibition and how it relates to gait adaptation in PwMS.

METHODS

Using transcranial magnetic stimulation (TMS), we assessed interhemispheric inhibition differences between the more affected and less affected hemisphere in the primary motor cortices in 29 PwMS. In addition, these same PwMS underwent a split-belt treadmill walking paradigm, with the faster paced belt moving under their more affected limb. Step length asymmetry (SLA) was the primary outcome measure used to assess gait adaptability during split-belt treadmill walking. We hypothesized that PwMS would exhibit differences in iSP inhibitory metrics between the more affected and less affected hemispheres and that increased interhemispheric inhibition would be associated with greater gait adaptability in PwMS.

RESULTS

No statistically significant differences in interhemispheric inhibition or conduction time were found between the more affected and less affected hemisphere. Furthermore, SLA aftereffect was negatively correlated with both average percent depth of silent period (dSP%AVE) (r = -0.40, p = 0.07) and max percent depth of silent period (dSP%MAX) r = -0.40, p = 0.07), indicating that reduced interhemispheric inhibition was associated with greater gait adaptability in PwMS.

CONCLUSION

The lack of differences between the more affected and less affected hemisphere indicates that PwMS have similar interhemispheric inhibitory capacity irrespective of the more affected hemisphere. Additionally, we identified a moderate correlation between reduced interhemispheric inhibition and greater gait adaptability. These findings may indicate that interhemispheric inhibition may in part influence responsiveness to motor adaptation paradigms and the need for further research evaluating the neural mechanisms underlying the relationship between interhemispheric inhibition and motor adaptability.

The effect of inherent and incidental constraints on bimanual force control in simulated Martian gravity

The ability to coordinate actions between the limbs is important for many operationally relevant tasks associated with space exploration. A future milestone in space exploration is sending humans to Mars. Therefore, an experiment was designed to examine the influence of inherent and incidental constraints on the stability characteristics associated with the bimanual control of force in simulated Martian gravity. A head-up tilt (HUT)/head-down tilt (HDT) paradigm was used to simulate gravity on Mars (22.3° HUT). Right limb dominant participants (N = 11) were required to rhythmically coordinate patterns of isometric forces in 1:1 in-phase and 1:2 multifrequency patterns by exerting force with their right and left limbs. Lissajous displays were provided to guide task performance. Participants performed 14 twenty-second practice trials at 90° HUT (Earth). Following a 30-min rest period, participants performed 2 test trials for each coordination pattern in both Earth and Mars conditions. Performance during the test trials were compared. Results indicated very effective temporal performance of the goal coordination tasks in both gravity conditions. However, results indicated differences associated with the production of force between Earth and Mars. In general, participants produced less force in simulated Martian gravity than in the Earth condition. In addition, force production was more harmonic in Martian gravity than Earth gravity for both limbs, indicating that less force distortions (adjustments, hesitations, and/or perturbations) occurred in the Mars condition than in the Earth condition. The force coherence analysis indicated significantly higher coherence in the 1:1 task than in the 1:2 task for all force frequency bands, with the highest level of coherence in the 1-4 Hz frequency band for both gravity conditions. High coherence in the 1-4 Hz frequency band is associated with a common neural drive that activates the two arms simultaneously and is consistent with the requirements of the two tasks. The results also support the notion that neural crosstalk stabilizes the performance of the 1:1 in-phase task. In addition, significantly higher coherence in the 8-12 Hz frequency bands were observed for the Earth condition than the Mars condition. Force coherence in the 8-12 Hz bands is associated with the processing of sensorimotor information, suggesting that participants were better at integrating visual, proprioceptive, and/or tactile feedback in Earth than for the Mars condition. Overall, the results indicate less neural interference in Martian gravity; however, participants appear to be more effective at using the Lissajous displays to guide performance under Earth's gravity.

Symmetry and synchrony of bimanual movements are not predicated on interlimb control coupling

Previous studies suggest that bimanual coordination recruits neural mechanisms that explicitly couple control of the arms, resulting in symmetric kinematics. However, the higher symmetry for actions that require congruous joint motions compared with noncongruous joint motions calls into question the concept of control coupling as a general policy. An alternative view proposes that codependence might emerge from an optimal feedback controller that minimizes control effort and costs in task performance. Support for this view comes from studies comparing conditions in which both hands move a shared or independent virtual objects. Because these studies have mainly focused on congruous bimanual movements, it remains unclear if kinematic symmetry emerges from such control policies. We now examine movements with congruous or noncongruous joint motions (inertially symmetric or asymmetric, respectively) under shared or independent cursors conditions. We reasoned that if a control policy minimizes kinematic differences between limbs, spatiotemporal symmetry should remain relatively unaffected by inertial asymmetries. As shared tasks reportedly elicit greater interlimb codependence, these conditions should elicit higher bilateral covariance regardless of inertial asymmetries. Our results indicate a robust spatiotemporal symmetry only under inertially symmetric conditions, regardless of cursor condition. We simulated bimanual reaching using an optimal feedback controller with and without explicit costs of kinematic asymmetry, finding that only the latter mirrored our empirical data. Our findings support the hypothesis that bimanual control policies do not include kinematic asymmetry as a cost when it is not demanded by task constraints suggesting that kinematic symmetry depends critically on mechanical movement conditions.NEW & NOTEWORTHY Previously, the control coupling hypothesis and task-dependent control hypothesis have been shown to be robust in the bimanually symmetrical movement, but whether the same policy remains robust in the bimanually asymmetrical movement remains unclear. Here, with evidence from empirical and simulation data, we show that a spatiotemporal symmetry between the arms is not predicated on control coupling, but instead it is predicated on the symmetry of mechanical conditions (e.g. limb inertia) between the arms.

People with Long Covid and ME/CFS Exhibit Similarly Impaired Dexterity and Bimanual Coordination: A Case-Case-Control Study

PURPOSE

Dexterity and bimanual coordination had not previously been compared between people with long COVID and people with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS). Therefore, this study determined dexterity and bimanual coordination in people with long COVID (∼16 month illness duration; n=21) and ME/CFS (∼16 year illness duration; n=20), versus age-matched healthy controls (n=20).

METHODS

Dexterity, and bimanual coordination was determined using the Purdue pegboard test.

RESULTS

The main findings of the present investigation were that people with ME/CFS and people with long COVID were generally comparable for Purdue pegboard tests (p>0.556 and d<0.36 for pairwise comparisons). It is worth noting however, that both these patient groups performed poorer in the Perdue pegboard test than healthy controls (p<0.169 and d>0.40 for pairwise comparisons).

CONCLUSIONS

These data suggest that both people with long COVID and people with ME/CFS have similarly impaired dexterity, and bimanual coordination. Therefore, there is an urgent need for interventions to target dexterity and bimanual coordination in people with ME/CFS, and given the current pandemic, people with long COVID.

Spontaneity competes with intention to influence the coordination dynamics of interpersonal performance tendencies

Research has shown that spontaneous visual coupling supports frequency entrainment, phase attraction, and intermittent interpersonal coordination when co-actors are switched from a no-vision (NV) to vision (V) context. In two experiments, co-actors started in a NV context while producing the same or different amplitude movements. The same amplitude resulted in similar self-paced frequencies, while different amplitudes resulted in disparate frequencies. In experiment 1, co-actors were instructed to maintain amplitude while receiving no instructions to coordinate their actions. Frequency and phase entrainment was limited in the V context even when co-actors started the NV context with the same amplitude. In experiment 2, co-actors were instructed to maintain amplitude and intentionally coordinate together, but not at a specific pattern. Significant frequency modulations occurred to maintain amplitude as the co-actors sought to coordinate their actions. With the open-ended instructions, co-actors produced in-phase and anti-phase coordination along with intermittent performance exhibited by shifts between a variety of stable relative phase patterns. The proposed hypotheses and findings are discussed within the context of a shared manifold representation for joint action contexts, with the coordination dynamics expressed by the HKB model of relative phase serving to conceptualization the representations in the shared manifold.

Facilitated adaptation via structural learning increases bimanual interference

Bimanual coordination is an essential feature of the motor system, yet interactions between the limbs during independent control remain poorly understood. Interference between the two hands, or the assimilation of movement characteristics between the two effectors, can be induced by perturbing one arm (e.g., via visuomotor rotation) and then measuring the effects in the contralateral limb. In this study, we sought to further determine the role adaptation plays in bimanual interference using a structural learning paradigm to alter feedback regulation in reaching. We trained healthy participants to counter 60 unique random rotations in right hand visual feedback over 240 reaches. Following this, we assessed feedforward and feedback measures of interference in a bimanual reaching task where the right hand was exposed to a fixed visual feedback rotation while the left hand reached without visual feedback. We found that participants who had been exposed to the structural training task in the right hand showed increased left hand interference during the first 20 trials of the test task. Moreover, interference was greater in feedback, rather than feedforward control parameters. The results further suggest that structural learning enhances bimanual interference via sensory feedback upregulation.

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.

NONAN GaitPrint: An IMU gait database of healthy young adults

An ongoing thrust of research focused on human gait pertains to identifying individuals based on gait patterns. However, no existing gait database supports modeling efforts to assess gait patterns unique to individuals. Hence, we introduce the Nonlinear Analysis Core (NONAN) GaitPrint database containing whole body kinematics and foot placement during self-paced overground walking on a 200-meter looping indoor track. Noraxon Ultium MotionTM inertial measurement unit (IMU) sensors sampled the motion of 35 healthy young adults (19-35 years old; 18 men and 17 women; mean ± 1 s.d. age: 24.6 ± 2.7 years; height: 1.73 ± 0.78 m; body mass: 72.44 ± 15.04 kg) over 18 4-min trials across two days. Continuous variables include acceleration, velocity, position, and the acceleration, velocity, position, orientation, and rotational velocity of each corresponding body segment, and the angle of each respective joint. The discrete variables include an exhaustive set of gait parameters derived from the spatiotemporal dynamics of foot placement. We technically validate our data using continuous relative phase, Lyapunov exponent, and Hurst exponent-nonlinear metrics quantifying different aspects of healthy human gait.

fMRI changes during multi-limb movements in Parkinson's disease

Background

While motor coordination problems are frequently reported among individuals with Parkinson’s disease (PD), the effects of the disease on the performance of multi-limb movements and the brain changes underlying impaired coordination are not well-documented.

Objective

Functional magnetic resonance imaging (fMRI) was used to examine differences in brain activity during a task that involved the coordination of non-homologous limbs (i.e., ipsilateral hand and foot) in individuals with and without PD.

Methods

Participants included 20 PD and 20 healthy control participants (HC). They were instructed to generate force in a coordinated manner by simultaneously contracting their ipsilateral hand and foot. PD were tested off their antiparkinsonian medication and on their more affected side, whereas the side in controls was randomized.

Results

Although both groups were able to coordinate the two limbs to produce the expected level of force, PD had a slower rate of force production and relaxation compared to HC. Additionally, their globus pallidus and primary motor cortex were underactive, whereas their pre-supplementary motor area (pre-SMA) and lateral cerebellum were overactive relative to HC. Importantly, in PD, the fMRI activity within the pre-SMA correlated with the rate of force decrease.

Conclusion

Multi-limb force control deficits in PD appear to be related to widespread underactivation within the basal ganglia-cortical loop. An overactivation of higher-level motor regions within the prefrontal cortex and lateral cerebellum may reflect increased cognitive control and performance monitoring that emerges during more complex motor tasks such as those that involve the coordination of multiple limbs.

Visual feedback decoding during bimanual circle drawing

The between-hand interference during bimanual tasks is a consequence of the connection between the neural controllers of movement. Previous studies showed the existence of an asymmetric between-hand interference (caused by neural cross talk) when different kinematics plans were to be executed by each hand or when only one was visually guided and received perturbed visual feedback. Here, in continuous bimanual circle drawing tasks, we investigated if the central nervous system (CNS) can benefit from visual composite feedback, i.e., a weighted sum of hands' positions presented for the visually guided hand, to control the nonvisible hand. Our results demonstrated improvement in the nonvisible nondominant hand (NDH) performance in the presence of the composite feedback. When NDH was visually guided, the dominant hand's (DH) performance during asymmetric drawing deteriorated, whereas its performance during symmetric drawing improved. This indicates that the CNS's ability to leverage composite feedback, which can be the result of decoding the nonvisible hand positional information from the composite feedback, is task-dependent and can be asymmetric. Also, the nonvisible hand's performance degraded when DH or NDH was visually guided with amplified error feedback. The results of the amplified feedback condition do not strongly support the asymmetry of the interference during asymmetric circle drawing. Comparing muscle activations in the asymmetric experiment, we concluded that the observed kinematic differences were not due to alternation in muscle co-contractions.NEW & NOTEWORTHY Many daily activities involve bimanual coordination while simultaneous movement of the hands may result in interference with their movements. Here, we studied whether the central nervous system could use the relevant information in composite feedback, i.e., a weighted sum of positional information of nonvisible and visible hands, to improve the movement of the nonvisible hand. Our results suggest the ability to decode and associate task-relevant information from the composite feedback.

Modulation of ipsilateral motor evoked potentials during bimanual coordination tasks

Introduction

Ipsilateral motor evoked potentials (iMEPs) are difficult to obtain in distal upper limb muscles of healthy participants but give a direct insight into the role of ipsilateral motor control.

Methods

We tested a new high-intensity double pulse transcranial magnetic stimulation (TMS) protocol to elicit iMEPs in wrist extensor and flexor muscles during four different bimanual movements (cooperative-asymmetric, cooperative-symmetric, non-cooperative-asymmetric and non-cooperative-symmetric) in 16 participants.

Results

Nine participants showed an iMEP in the wrist extensor in at least 20% of the trials in each of the conditions and were classified as iMEP+ participants. iMEP persistence was greater for cooperative (50.5 ± 28.8%) compared to non-cooperative (31.6 ± 22.1%) tasks but did not differ between asymmetric and symmetric tasks. Area and amplitude of iMEPs were also increased during cooperative (area = 5.41 ± 3.4 mV × ms; amplitude = 1.60 ± 1.09 mV) compared to non-cooperative (area = 3.89 ± 2.0 mV × ms; amplitude = 1.12 ± 0.56 mV) tasks and unaffected by task-symmetry.

Discussion

The upregulation of iMEPs during common-goal cooperative tasks shows a functional relevance of ipsilateral motor control in bimanual movements. The paired-pulse TMS protocol is a reliable method to elicit iMEPs in healthy participants and can give new information about neural control of upper limb movements. With this work we contribute to the research field in two main aspects. First, we describe a reliable method to elicit ipsilateral motor evoked potentials in healthy participants which will be useful in further advancing research in the area of upper limb movements. Second, we add new insight into the motor control of bimanual movements. We were able to show an upregulation of bilateral control represented by increased ipsilateral motor evoked potentials in cooperative, object-oriented movements compared to separate bimanual tasks. This result might also have an impact on neurorehabilitation after stroke.

Bilateral arm movements are coordinated via task-dependent negotiations between independent and codependent control, but not by a "coupling" control policy

Prior research has shown that coordination of bilateral arm movements might be attributed to either control policies that minimize performance and control costs regardless of bilateral symmetry or by control coupling, which activates bilaterally homologous muscles as a single unit to achieve symmetric performance. We hypothesize that independent bimanual control (movements of one arm are performed without influence on the other) and codependent bimanual control (two arms are constrained to move together with high spatiotemporal symmetry) are two extremes on a coordination spectrum that can be negotiated to meet infinite variations in task demands. To better understand and distinguish between these views, we designed a task where minimization of either control costs or asymmetry would yield different patterns of coordination. Participants made bilateral reaches with a shared visual cursor to a midline target. We then covertly varied the gain contribution of either hand to the shared cursor's horizontal position. Across two experiments, we show that bilateral coordination retains high task-dependent sensitivity to subtle visual feedback gain asymmetries applied to the shared cursor. Specifically, we found a change from strong spatial covariation between hands during equal gains to more independent control during asymmetric gains, which occurred rapidly and with high specificity to the dimension of gain manipulation. Furthermore, the extent of spatial covariation was graded to the magnitude of perpendicular gain asymmetry between hands. These findings suggest coordination of bilateral arm movements flexibly maneuvers along a continuous coordination spectrum in a task-dependent manner that cannot be explained by bilateral control coupling.NEW & NOTEWORTHY Minimization of performance and control costs and efferent coupling between bilaterally homologous muscle groups have been separately hypothesized to describe patterns of bimanual coordination. Here, we address whether the mechanisms mediating independent and codependent control between limbs can be weighted for successful task performance. Using bilaterally asymmetric visuomotor gain perturbations, we show bimanual coordination can be characterized as a negotiation along a spectrum between extremes of independent and codependent control, but not efferent control coupling.

Dissociating haptic feedback from physical assistance does not improve motor performance

In robots for motor rehabilitation and sports training, haptic assistance typically provides both mechanical guidance and task-relevant information. With the natural human tendency to minimise metabolic cost, mechanical guidance may however prevent efficient short term learning and retention. In this work, we explore the effect of providing haptic feedback to the not active hand during a tracking task. We test four types of haptic feedback: task- or error-related information, no information and irrelevant information. The results show that feedback provided to the hand not carrying out the tracking task did not improve task performance. However, irrelevant information to the task worsened performance, and negatively influenced the participants' perception of helpfulness, assistance, likability and predictability.

The Role of the Corpus Callosum (Micro)Structure in Bimanual Coordination: A Literature Review Update

The characterization of callosal white matter is crucial for understanding the relationship between brain structure and bimanual motor function. An earlier literature review established this. With advancements in neuroimaging and data modeling, we aim to provide an update on the existing literature. Firstly, we highlight new CC parcellation approaches, such as functional MRI- and atlas-informed tractography and in vivo histology. Secondly, we elaborate on recent insights into the CC's role in bimanual coordination, drawing evidence from studies on healthy young and older adults, patients and training-related callosal plasticity. We also reflect on progress in the field and propose future perspectives to inspire research on the underlying mechanisms of structural-functional interactions.

Motor performance in joint action tasks: The impact of dyadic motive fit

In many daily situations, two or more individuals need to coordinate their actions to achieve a common goal and perform successfully. Past research on joint action has predominantly focused on the question of how such interactions are accomplished. Here we focus on the impact of inter-individual, trait-like differences to predict joint action performance. More specifically, we examined whether performance in a joint action task is moderated by the (in)congruence of individuals' motive dispositions. To this end, 27 dyads performed a joint action task in which they had to navigate a ball through a maze with each partner using a joystick and each being responsible for either moving the ball along the x-axis or the y-axis. As dependent measures, we analyzed dyads' performance (times and errors). As trait-like predictors, we assessed implicit and explicit motives by means of the Picture Story Exercise and the Unified Motive Scale, respectively. Linear regression modeling revealed that congruent explicit affiliation motives predict faster best times and that higher congruent implicit achievement motives are associated with reduced errors. Exploratory Response Surface Analyses yielded identical results for the affiliation motive. These findings provide initial evidence to suggest that interindividual differences and in motives as well as their fit are related to joint action performance. Future directions of this new paradigm and novel ways to analyze dyadic motive fits and their relation to joint action performance are discussed.

A Three-Fold Integrated Perspective on Healthy Development: An Opinion Paper

Mental health and wellbeing are increasingly threatened in the current post-pandemic times, with stress, especially in students, reaching preoccupying levels. In addition, while many educational programs are unidimensional (i.e., lacking integration between physical, emotional and cognitive elements), there are ways to promote physical, social and mental health in children and adolescents. In this opinion paper, we will discuss the importance of an integrative approach for health development and examine relevant factors, such as awareness and emotional intelligence. We will highlight evidence ranging from behavioral to electrophysiological, structural and molecular, and report several recent studies supporting the effectiveness of a holistic approach in supporting wellbeing and creativity in children and adults, and detailing a specific paradigm named the Quadrato Motor Training (QMT). QMT is a specifically structured movement meditation, involving cognitive, motor and affective components. Finally, we will support a holistic view on education, integrating motion, emotion and cognition to develop a person-centered, or in this case student-centered, approach to wellbeing and health.

The effect of elastic and viscous force fields on bimanual coordination

Bimanual in-phase and anti-phase coordination modes represent two basic movement patterns with distinct characteristics-homologous muscle contraction and non-homologous muscle contraction, respectively. A method to understand the contribution of each limb to the overall coordination pattern involves detuning (Δω) the natural eigenfrequency of each limb. In the present experiment, we experimentally broke the symmetry between the two upper limbs by adding elastic and viscous force fields using a Kinarm robot exoskeleton. We measured the effect of this symmetry breaking on coordination stability as participants performed bimanual in-phase and anti-phase movements using their left and right hand in 1:1 frequency locking mode. Differences between uncoupled frequencies were manipulated via the application of viscous & elastic force fields and using fast and slow oscillation frequencies with a custom task developed using the Kinarm robotic exoskeleton. The effects of manipulating the asymmetry between the limbs were measured through the mean and variability of relative phase (ϕ) from the intended modes of 0 ° or 180 °. In general, participants deviated less from intended phase irrespective of coordination mode in all matched conditions, except for when elastic loads are applied to both arms in the anti-phase coordination. Second, we found that when force fields were mismatched participants exhibited a larger deviation from the intended phase. Overall, there was increased phase deviation during anti-phase coordination. Finally, participants exhibited higher variability in relative phase in mismatched force conditions compared to matched force conditions, with overall higher variability during anti-phase coordination mode. We extend previous research by demonstrating that symmetry breaking caused by force differences between the limbs disrupts stability in each coordination mode.

Sex differences in the neural underpinnings of unimanual and bimanual control in adults

While many of the movements we make throughout our day involve just one upper limb, most daily movements require a certain degree of coordination between both upper limbs. Historically, sex differences in eye-hand coordination have been observed. As well, there are demonstrated sex-specific differences in hemisphere symmetry, interhemispheric connectivity, and motor cortex organization. While it has been suggested that these anatomical differences may underlie sex-related differences in performance, sex differences in the functional neural correlate underlying bimanual performance have not been explicitly investigated. In the current study we tested the hypothesis that the functional connectivity underlying bimanual movement control differed depending on the sex of an individual. Participants underwent MRI scanning to acquire anatomical and functional brain images. During the functional runs, participants performed unimanual and bimanual coordination tasks using two button boxes. The tasks included pressing the buttons in time to an auditory cue with either their left or their right hand individually (unimanual), or with both hands simultaneously (bimanual). The bimanual task was further divided into either an in-phase (mirror/symmetrical) or anti-phase (parallel/asymmetrical) condition. Participants were provided with extensive training to ensure task comprehension, and performance error rates were found to be equivalent between men and women. A generalized psychophysiological interaction (gPPI) analysis was implemented to examine how functional connectivity in each condition was modulated by sex. In support of our hypothesis, women and men demonstrated differences in the neural correlates underlying unimanual and bimanual movements. In line with previous literature, functional connectivity patterns showed sex-related differences for right- vs left-hand movements. Sex-specific functional connectivity during bimanual movements was not a sum of the functional connectivity underlying right- and left-hand unimanual movements. Further, women generally showed greater interhemispheric functional connectivity across all conditions compared to men and had greater connectivity between task-related cortical areas, while men had greater connectivity involving the cerebellum. Sex differences in brain connectivity were associated with both unimanual and bimanual movement control. Not only do these findings provide novel insight into the fundamentals of how the brain controls bimanual movements in both women and men, they also present potential clinical implications on how bimanual movement training used in rehabilitation can best be tailored to the needs of individuals.

Dual-site TMS as a tool to probe effective interactions within the motor network: a review

Dual-site transcranial magnetic stimulation (ds-TMS) is well suited to investigate the causal effect of distant brain regions on the primary motor cortex, both at rest and during motor performance and learning. However, given the broad set of stimulation parameters, clarity about which parameters are most effective for identifying particular interactions is lacking. Here, evidence describing inter- and intra-hemispheric interactions during rest and in the context of motor tasks is reviewed. Our aims are threefold: (1) provide a detailed overview of ds-TMS literature regarding inter- and intra-hemispheric connectivity; (2) describe the applicability and contributions of these interactions to motor control, and; (3) discuss the practical implications and future directions. Of the 3659 studies screened, 109 were included and discussed. Overall, there is remarkable variability in the experimental context for assessing ds-TMS interactions, as well as in the use and reporting of stimulation parameters, hindering a quantitative comparison of results across studies. Further studies examining ds-TMS interactions in a systematic manner, and in which all critical parameters are carefully reported, are needed.

A Scoping Review on Movement, Neurobiology and Functional Deficits in Dyslexia: Suggestions for a Three-Fold Integrated Perspective

Developmental dyslexia is a common complex neurodevelopmental disorder. Many theories and models tried to explain its symptomatology and find ways to improve poor reading abilities. The aim of this scoping review is to summarize current findings and several approaches and theories, focusing on the interconnectedness between motion, emotion and cognition and their connection to dyslexia. Consequently, we present first a brief overview of the main theories and models regarding dyslexia and its proposed neural correlates, with a particular focus on cerebellar regions and their involvement in this disorder. After examining different types of intervention programs and remedial training, we highlight the effects of a specific structured sensorimotor intervention named Quadrato Motor Training (QMT). QMT utilizes several cognitive and motor functions known to be relevant in developmental dyslexia. We introduce its potential beneficial effects on reading skills, including working memory, coordination and attention. We sum its effects ranging from behavioral to functional, structural and neuroplastic, especially in relation to dyslexia. We report several recent studies that employed this training technique with dyslexic participants, discussing the specific features that distinguish it from other training within the specific framework of the Sphere Model of Consciousness. Finally, we advocate for a new perspective on developmental dyslexia integrating motion, emotion and cognition to fully encompass this complex disorder.

The effect of initiation prediction and non-prediction on muscle relaxation control

[Purpose] This study aimed to examine the difference in the excitability of the primary motor cortex between initiation-predictive and non-predictive tasks, where the onset of muscle relaxation is predicted and not predicted, respectively. [Participants and Methods] Seventeen participants were asked to perform rapid muscle relaxation either through an initiation-predictive or non-predictive task. The baseline was set at 20 percent of the maximum voluntary contraction. Motor-evoked potentials and H-reflexes elicited by transcranial magnetic stimulation and median nerve electrical stimulation, respectively, were measured. The mean stimulation time from the onset of relaxation was calculated, and the motor-evoked potentials and Hoffmann's reflexes elicited during the first (immediately before relaxation) and second half (long before relaxation) were compared. [Results] The amplitude of the motor-evoked potential significantly increased in both initiation-predictive and non-predictive tasks when compared to the baseline, indicating increased excitability of the primary motor cortex. The motor-evoked potential from the initiation-non-predictive task, but not the initiation-predictive task, was associated with increased excitability of the primary motor cortex immediately before relaxation. [Conclusion] Variations in the predictability of motor movements are associated with changes in muscle relaxation control in the central nervous system.

Upper and lower motor neuron neurophysiology and motor control

This chapter considers the principles that underlie neurophysiological studies of upper motor neuron or lower motor neuron lesions, based on an understanding of the normal structure and function of the motor system. Human motor neurophysiology consists of an evaluation of the active components of the motor system that are relevant to volitional movements. Relatively primitive motor skills include locomotion, much dependent on the spinal cord central pattern generator, reaching, involving proximal and distal muscles activation, and grasping. Humans are well prepared to perform complex movements like writing. The role of motor cortex is critical for the motor activity, very dependent on the continuous sensory feedback, and this is essential for adapting the force and speed control, which contributes to motor learning. Most corticospinal neurons in the brain project to brainstem and spinal cord, many with polysynaptic inhibitory rather than excitatory connections. The monosynaptic connections observed in humans and primates constitute a specialized pathway implicated in fractional finger movements. Spinal cord has a complex physiology, and local reflexes and sensory feedback are essential to control adapted muscular contraction during movement. The cerebellum has a major role in motor coordination, but also consistent roles in sensory activities, speech, and language, in motor and spatial memory, and in psychological activity. The motor unit is the final effector of the motor drive. The complex interplay between the lower motor neuron, its axon, motor end-plates, and muscle fibers allows a relevant plasticity in the movement output.

Overt visual attention and between-limb asynchrony for bimanual reaching movements

Although synchrony between the limbs is an often-cited feature of bimanual coordination, recent studies have also highlighted the small asynchronies that can occur. The visuo-motor demands of any bimanual task are considered central to the emergence of asynchrony, but the relationship between the two remains largely unexplored. This study aimed to address this issue. Hand and eye movements were measured in 19 participants, while they made either unimanual or bimanual reach-to-point (aiming) movements to targets presented on a touchscreen. Bimanual movements were either congruent (same-sized targets) or incongruent (different-sized targets). Resulting hand data showed many of the typical patterns of movement previously reported. While temporal coupling between the limbs remained largely evident for bimanual movements, small between-limb asynchronies were apparent and demonstrated clear associations with the competing precision requirements of the targets and related visual attention. Participants mainly directed their gaze towards the more difficult target with corresponding reaching movements demonstrating greater precision than for the easier target. Additionally, there was a reliable tendency for the hand reaching towards the more difficult target to lead. Importantly, it was the competing visuo-motor demands of individual movements rather than overall difficulty that resulted in greater between-limb asynchrony; accordingly, where both targets were small (i.e., the most difficult condition), asynchrony was significantly less pronounced than for incongruent bimanual conditions. The results show how the visuo-motor system balances its apparent drive for synchrony in coordinating bimanual movements with the competing demands that characterise the constituent unimanual movements.

How virtual and mechanical coupling impact bimanual tracking

Bilateral training systems look to promote the paretic hand's use in individuals with hemiplegia. Although this is normally achieved using mechanical coupling (i.e., a physical connection between the hands), a virtual reality system relying on virtual coupling (i.e., through a shared virtual object) would be simpler to use and prevent slacking. However, it is not clear whether different coupling modes differently impact task performance and effort distribution between the hands. We explored how 18 healthy right-handed participants changed their motor behaviors in response to the uninstructed addition of mechanical coupling, and virtual coupling using a shared cursor mapped to the average hands' position. In a second experiment, we then studied the impact of connection stiffness on performance, perception, and effort imbalance. The results indicated that both coupling types can induce the hands to actively contribute to the task. However, the task asymmetry introduced by using a cursor mapped to either the left or right hand only modulated the hands' contribution when not mechanically coupled. The tracking performance was similar for all coupling types, independent of the connection stiffness, although the mechanical coupling was preferred and induced the hands to move with greater correlation. These findings suggest that virtual coupling can induce the hands to actively contribute to a task in healthy participants without hindering their performance. Further investigation on the coupling types' impact on the performance and hands' effort distribution in patients with hemiplegia could allow for the design of simpler training systems that promote the affected hand's use.NEW & NOTEWORTHY We showed that the uninstructed addition of a virtual and/or a mechanical coupling can induce both hands to actively contribute in a continuous redundant bimanual tracking task without impacting performance. In addition, we showed that the task asymmetry can only alter the effort distribution when the hands are not connected, independent of the connection stiffness. Our findings suggest that virtual coupling could be used in the development of simpler VR-based training devices.

Transcranial direct current stimulation influences repetitive bimanual force control and interlimb force coordination

This study aimed to investigate the potential effect of bilateral transcranial direct current stimulation (tDCS) on repetitive bimanual force control and force coordination in healthy young adults. In this sham-controlled crossover study, 18 right-handed young adults were enrolled. Repetitive bimanual handgrip force control trials were performed by the participants at 40% of maximum voluntary contraction until task failure. We randomly provided bilateral active and sham tDCS to the primary motor cortex (M1) of each participant before conducting the repetitive bimanual force control task. We quantified the number of successful trials to assess the ability to maintain bimanual force control across multiple trials. Moreover, we estimated bimanual force control and force coordination by quantifying force accuracy, variability, regularity, and correlation coefficient in maximal and adjusted successful trials. Force asymmetry was calculated to examine potential changes in motor dependency on each hand during the task. Bilateral tDCS significantly increased the number of successful trials compared with sham tDCS. The adjusted successful trial revealed that participants who received bilateral tDCS maintained better bimanual force control and coordination, as indicated by decreased force variability and regularity as well as more negative correlation coefficient values in comparison with sham condition. Moreover, participants who received bilateral tDCS produced more force from the dominant hand than from the nondominant hand in both maximal and adjusted successful trials. These findings suggest that bilateral tDCS on M1 successfully maintains bimanual force control with better force coordination by modulating motor dependency.

Lower Limb Asymmetry Evaluation Using the Balance Tracking System (BTrackS) Single Leg Stance Protocol

Single Leg Stance (SLS) balance testing is a common means of determining lower limb asymmetries in motor behavior. The Balance Tracking System (BTrackS) Balance Plate is a low-cost, portable force plate for objectively obtaining balance measurements. The present study provides the first known balance results for the BTrackS SLS protocol. BTrackS SLS testing was conducted on 161 young adults (90 women, 71 men) according to the test's standardized instructions. Specifically, participants performed one-legged (left or right) stance on the BTrackS Balance Plate for four, (2 practice, 2 actual) 20 s trials. SLS test outputs included total Center of Pressure path length and absolute symmetry index. Results showed that women had better SLS performance than men and that both sexes performed better on the actual compared to practice trial. Systematic one-sample t-tests of the Absolute Symmetry Index measures showed that a difference of 16% or greater between legs represented asymmetric performance. These results have clear value for individuals using BTrackS SLS testing to evaluate potential asymmetries. Additionally, these findings agree with previous reports showing sex differences favoring women on tests of static balance, and validate the use of a practice trial in the BTrackS SLS protocol.

Higher visual gain contributions to bilateral motor synergies and force control

This study investigated the effects of altered visual gain levels on bilateral motor synergies determined by the uncontrolled manifold (UCM) hypothesis and force control. Twelve healthy participants performed bimanual index finger abduction force control tasks at 20% of their maximal voluntary contraction across four different visual gain conditions: 8, 80, 256, and 512 pixels/N. Quantifying force accuracy and variability within a trial provided a bimanual force control outcome. The UCM analysis measured bilateral motor synergies, a proportion of good variance to bad variance across multiple trials. Correlation analyses determined whether changes in the UCM variables were related to changes in force control variables from the lowest to highest visual gain conditions, respectively. Multiple analyses indicated that the three highest visual gain conditions in comparison to the lowest visual gain increased values of bilateral motor synergies and target force accuracy. The correlation findings showed that a reduction of bad variance from the lowest to three highest visual gain conditions was related to increased force accuracy. These findings reveal that visual gain greater than 8 pixels/N facilitates bimanual force control.

The influence of distal and proximal muscle activation on neural crosstalk

Previous research has indicated that neural crosstalk is asymmetric, with the dominant effector exerting a stronger influence on the non-dominant effector than vice versa. Recently, it has been hypothesized that this influence is more substantial for proximal than distal effectors. The current investigation was designed to determine the effects of distal ((First Dorsal Interosseous (FDI)) and proximal (triceps brachii (TBI)) muscle activation on neural crosstalk. Twelve right-limb dominant participants (mean age = 21.9) were required to rhythmically coordinate a 1:2 pattern of isometric force guided by Lissajous displays. Participants performed 10, 30 s trials with both distal and proximal effectors. Coherence between the two effector groups were calculated using EMG-EMG wavelet coherence. The results indicated that participants could effectively coordinate the goal coordination pattern regardless of the effectors used. However, spatiotemporal performance was more accurate when performing the task with distal than proximal effectors. Force distortion, quantified by harmonicity, indicated that more perturbations occurred in the non-dominant effector than in the dominant effector. The results also indicated significantly lower harmonicity for the non-dominant proximal effector compared to the distal effectors. The current results support the notion that neural crosstalk is asymmetric in nature and is greater for proximal than distal effectors. Additionally, the EMG-EMG coherence results indicated significant neural crosstalk was occurring in the Alpha bands (5-13 Hz), with higher values observed in the proximal condition. Significant coherence in the Alpha bands suggest that the influence of neural crosstalk is occurring at a subcortical level.

Front crawl swimming coordination: a systematic review

Several constraints, including environmental (e.g., aquatic resistance, temperature and viscosity), organismic (e.g., anthropometry, buoyancy) and task-related (e.g., imposed swim speed or stroke rate) impact motor coordination and swimming performance. As motor coordination requires structurally organising intra- and inter-limb coupling, the purpose of this review was to update the literature concerning coordination between the upper-limbs in front crawl swimming. We focused on the effects of biomechanical, physiological, and personal (gender, skill level, and age) factors on coordination and performance. In fact, it could be highlighted that upper-limbs coordination varies with organismic, task and environmental constraints, resulting in several available motor solutions that should be adopted according to how each swimmer deals with occurring constraints. As such, there is no ideal or optimal coordination pattern that youth, learners and less-skilled swimmers should imitate.

Spectral properties of physiological mirror activity: an investigation of frequency features and common input between homologous muscles

During unilateral contractions, muscular activation can be detected in both active and resting limbs. In healthy populations, the latter is referred to as physiological mirror activity (pMA). The study of pMA holds implications for clinical applications as well as the understanding of bilateral motor control. However, the underlying mechanisms of pMA remain to be fully resolved. A commonality of prevailing explanatory approaches is the concept of shared neural input. With this study, we, therefore, aimed to investigate neural input in the form of multiple analyses of surface electromyography (sEMG) recordings in the frequency domain. For this purpose, 14 healthy, right-handed males aged 18–35 years were recruited. All participants performed a pinch-force task with the dominant hand in a blockwise manner. In total, 9 blocks of 5 contractions each were completed at 80% of maximum force output. Muscle activity was recorded via sEMG of the first dorsal interosseous muscle of the active and resting hand. We analyzed (1) spectral features as well as (2) intermuscular coherence (IMC). Our results demonstrate a blockwise increase in median frequency, mean frequency, and peak frequency in both hands. Frequency ratio analyses revealed a higher low-frequency component in the resting hand. Although we were able to demonstrate IMC on an individual level, results varied greatly and grand-averaged IMC failed to reach significance. Taken together, our findings imply an overlap of spectral properties between active and passive hands during repeated unilateral contractions. Combined with evidence from previous studies, this suggests a common neural origin between active and resting hands during unilateral contractions possibly resulting from a reduction in interhemispheric inhibition due to high force demands. Nevertheless, the exploratory nature of this study necessitates the classification of our results through follow-up studies.

Encoder-Controlled Functional Electrical Stimulator for Bilateral Wrist Activities—Design and Evaluation

Upper limb impairment following stroke is often characterized by limited voluntary control in the affected arm. In addition, significant motor coordination problems occur on the unaffected arm due to avoidance of performing bilateral symmetrical activities. Rehabilitation strategies should, therefore, not only aim at improving voluntary control on the affected arm, but also contribute to synchronizing activity from both upper limbs. The encoder-controlled functional electrical stimulator, described in this paper, implements precise contralateral control of wrist flexion and extension with electrical stimulation. The stimulator is calibrated for each individual to obtain a table of stimulation parameters versus wrist angle. This table is used to set stimulation parameters dynamically, based on the difference in wrist angle between the set and stimulated side, which is continuously monitored. This allows the wrist on the stimulated side to follow flexion and extension patterns on the set side, thereby mirroring wrist movements of the normal side. This device also gives real-time graphical feedback on how the stimulated wrist is performing in comparison to the normal side. A study was performed on 25 normal volunteers to determine how closely wrist movements on the set side were being followed on the stimulated side. Graphical results show that there were minor differences, which were quantified by considering the peak angles of flexion and extension on the set and stimulated side for each participant. The mean difference in peak flexion and extension range of movement was 2.3 degrees and 1.9 degrees, respectively, with a mean time lag of 1 s between the set and the stimulated angle graphs.

Bimanual coordination during reach-to-grasp actions is sensitive to task goal with distinctions between left- and right-hemispheric stroke

The perceptual feature of a task such as how a task goal is perceived influences performance and coordination of bimanual actions in neurotypical adults. To assess how bimanual task goal modifies paretic and non-paretic arm performance and bimanual coordination in individuals with stroke affecting left and right hemispheres, 30 participants with hemispheric stroke (15 right-hemisphere damage-RHD); 15 left-hemisphere damage-LHD) and 10 age-matched controls performed reach-to-grasp and pick-up actions under bimanual common-goal (i.e., two physically coupled dowels), bimanual independent-goal (two physically uncoupled dowels), and unimanual conditions. Reach-to-grasp time and peak grasp aperture indexed motor performance, while time lags between peak reach velocities, peak grasp apertures, and peak pick-up velocities of the two hands characterized reach, grasp, and pick-up coordination, respectively. Compared to unimanual actions, bimanual actions significantly slowed non-paretic arm speed to match paretic arm speed, thus affording no benefit to paretic arm performance. Detriments in non-paretic arm performance during bimanual actions was more pronounced in the RHD group. Under common-goal conditions, movements were faster with smaller peak grasp apertures compared to independent-goal conditions for all groups. Compared to controls, individuals with stroke demonstrated poor grasp and pick-up coordination. Of the patient groups, patients with LHD showed more pronounced deficits in grasp coordination between hands. Finally, grasp coordination deficits related to paretic arm motor deficits (upper extremity Fugl-Meyer score) for LHD group, and to Trail-Making Test performance for RHD group. Findings suggest that task goal and distinct clinical deficits influence bimanual performance and coordination in patients with left- and right-hemispheric stroke.

Bridging cognition and action: executive functioning mediates the relationship between white matter fiber density and complex motor abilities in older adults

Aging may be associated with motor decline that is attributed to deteriorating white matter microstructure of the corpus callosum (CC), among other brain-related factors. Similar to motor functioning, executive functioning (EF) typically declines during aging, with age-associated changes in EF likewise being linked to altered white matter connectivity in the CC. Given that both motor and executive functions rely on white matter connectivity via the CC, and that bimanual control is thought to rely on EF, the question arises whether EF can at least party account for the proposed link between CC-connectivity and motor control in older adults. To address this, diffusion magnetic resonance imaging data were obtained from 84 older adults. A fiber-specific approach was used to obtain fiber density (FD), fiber cross-section (FC), and a combination of both metrics in eight transcallosal white matter tracts. Motor control was assessed using a bimanual coordination task. EF was determined by a domain-general latent EF-factor extracted from multiple EF tasks, based on a comprehensive test battery. FD of transcallosal prefrontal fibers was associated with cognitive and motor performance. EF partly accounted for the relationship between FD of prefrontal transcallosal pathways and motor control. Our results underscore the multidimensional interrelations between callosal white matter connectivity (especially in prefrontal brain regions), EF across multiple domains, and motor control in the older population. They also highlight the importance of considering EF when investigating brain-motor behavior associations in older adults.

The correlations between kinematic profiles and cerebral hemodynamics suggest changes of motor coordination in single and bilateral finger movement

Objective

The correlation between the performance of coordination movement and brain activity is still not fully understood. The current study aimed to identify activated brain regions and brain network connectivity changes for several coordinated finger movements with different difficulty levels and to correlate the brain hemodynamics and connectivity with kinematic performance.

Methods

Twenty-one right-dominant-handed subjects were recruited and asked to complete circular motions of single and bilateral fingers in the same direction (in-phase, IP) and in opposite directions (anti-phase, AP) on a plane. Kinematic data including radius and angular velocity at each task and synchronized blood oxygen concentration data using functional near-infrared spectroscopy (fNIRS) were recorded covering six brain regions including the prefrontal cortex, motor cortex, and occipital lobes. A general linear model was used to locate activated brain regions, and changes compared with baseline in blood oxygen concentration were used to evaluate the degree of brain region activation. Small-world properties, clustering coefficients, and efficiency were used to measure information interaction in brain activity during the movement.

Result

It was found that the radius error of the dominant hand was significantly lower than that of the non-dominant hand (p < 0.001) in both clockwise and counterclockwise movements. The fNIRS results confirmed that the contralateral brain region was activated during single finger movement and the dominant motor area was activated in IP movement, while both motor areas were activated simultaneously in AP movement. The Δhbo were weakly correlated with radius errors (p = 0.002). Brain information interaction in IP movement was significantly larger than that from AP movement in the brain network (p < 0.02) in the right prefrontal cortex. Brain activity in the right motor cortex reduces motor performance (p < 0.001), while the right prefrontal cortex region promotes it (p < 0.05).

Conclusion

Our results suggest there was a significant correlation between motion performance and brain activation level, as well as between motion deviation and brain functional connectivity. The findings may provide a basis for further exploration of the operation of complex brain networks.

Hand preferences in coordinated bimanual tasks in non-human primates: A systematic review and meta-analysis

The evolutionary significance of hand preferences among non-human primates and humans has been studied for decades with the aim of determining the origins of the population-level tendency. In this study, a meta-analysis was conducted to statistically integrate data on hand preferences in non-human primates performing the tube task and other bimanual tasks to determine the presence and direction of manual laterality. Significant individual-level lateralization was obtained for these bimanual tasks. In nonhuman primates, 82% of the animals analysed showed right or left-hand preference performing the tube task, this figure being 90% for other bimanual tasks. In contrast with humans, no asymmetry was found at the population level. Additionally, population-level preferences were not found in either of the tasks, although a strong manual preference was found when performing the tube task and other bimanual tasks. Species was studied as a variable moderator throughout the meta-analysis. These results highlight the importance of standardized testing methodologies across species and institutions to obtain comparable data and fill the gaps in the taxonomy.

Non-invasive brain stimulation for improving gait, balance, and lower limbs motor function in stroke

Objectives

This systematic review and meta-analysis aim to summarize and analyze the available evidence of non-invasive brain stimulation/spinal cord stimulation on gait, balance and/or lower limb motor recovery in stroke patients.

Methods

The PubMed database was searched from its inception through to 31/03/2021 for randomized controlled trials investigating repetitive transcranial magnetic stimulation or transcranial/trans-spinal direct current/alternating current stimulation for improving gait, balance and/or lower limb motor function in stroke patients.

Results

Overall, 25 appropriate studies (including 657 stroke subjects) were found. The data indicates that non-invasive brain stimulation/spinal cord stimulation is effective in supporting recovery. However, the effects are inhomogeneous across studies: (1) transcranial/trans-spinal direct current/alternating current stimulation induce greater effects than repetitive transcranial magnetic stimulation, and (2) bilateral application of non-invasive brain stimulation is superior to unilateral stimulation.

Conclusions

The current evidence encourages further research and suggests that more individualized approaches are necessary for increasing effect sizes in stroke patients.

Associations of cardiorespiratory fitness and exercise with brain white matter in healthy adults: A systematic review and meta-analysis

Magnetic resonance imaging (MRI) studies have revealed positive associations between brain structure and physical activity, cardiorespiratory fitness, and exercise (referred to here as PACE). While a considerable body of research has investigated the effects of PACE on grey matter, much less is known about effects on white matter (WM). Hence, we conducted a systematic review of peer-reviewed literature published prior to 5^th July 2021 using online databases (PubMed and Scopus) and PRISMA guidelines to synthesise what is currently known about the relationship between PACE and WM in healthy adults. A total of 60 studies met inclusion criteria and were included in the review. Heterogeneity across studies was calculated using Qochran's q test, and publication bias was assessed for each meta-analysis using Begg and Mazumdar rank correlation test. A meta-regression was also conducted to explore factors contributing to any observed heterogeneity. Overall, we observed evidence of positive associations between PACE and global WM volume (effect size (Hedges's g) = 0.137, p < 0.001), global WM anomalies (effect size = 0.182, p < 0.001), and local microstructure integrity (i.e., corpus callosum: effect size = 0.345, p < 0.001, and anterior limb of internal capsule: effect size = 0.198, p < 0.001). These findings suggest that higher levels of PACE are associated with improved global WM volume and local integrity. We appraise the quality of evidence, and discuss the implications of these findings for the preservation of WM across the lifespan. We conclude by providing recommendations for future research in order to advance our understanding of the specific PACE parameters and neurobiological mechanisms underlying these effects.

Age and Interlimb Coordination Complexity Modulate Oscillatory Spectral Dynamics and Large-scale Functional Connectivity

Interlimb coordination deteriorates as a result of aging. Due to its ubiquity in daily life, a greater understanding of the underlying neurophysiological changes is required. Here, we combined electroencephalography time-frequency spectral power and functional connectivity analyses to provide a comprehensive overview of the neural dynamics underlying the age-related deterioration of interlimb coordination involving all four limbs. Theta, alpha and beta oscillations in the frontal, central and parietal regions were analyzed in twenty younger (18-30 years) and nineteen older adults (65-78 years) during a complex interlimb reaction time task. Reaction time was significantly higher in older adults across all conditions, and the discrepancy between both age groups was largest in the most complex movement condition. Older adults demonstrated enhanced beta event-related desynchronization (i.e., the attenuation of beta power), which further increased along with task complexity and was positively linked to behavioral performance. Theta functional connectivity between frontal, central and parietal regions generally increased with movement complexity, irrespective of age group. In general, frontoparietal alpha band functional connectivity tended to be reduced in older versus younger adults, although these contrasts did not survive multiple comparison corrections. Overall, spectral results suggest that enhanced beta desynchronization in older adults reflects a successful compensatory mechanism to cope with increased difficulty during complex interlimb coordination. Functional connectivity results suggest that theta and alpha band connectivity are prone to respectively task- and age-related modulations. Future work could target these spectral and functional connectivity dynamics through noninvasive brain stimulation to potentially improve interlimb coordination in older adults.

Microstructural alterations predict impaired bimanual control in Parkinson’s disease

Bimanual coordination is impaired in Parkinson’s disease affecting patients’ ability to perform activities of daily living and to maintain independence. Conveyance of information between cortical and subcortical areas is essential for bimanual coordination and relies on the integrity of cerebral microstructure. As pathological deposition of alpha-synuclein compromises microstructure in Parkinson’s disease, we investigated the relationship between microstructural integrity and bimanual coordination using diffusion-weighted MRI in 23 patients with Parkinson’s disease (mean age ± standard deviation: 56.0 ± 6.45 years; 8 female) and 26 older adults (mean age ± standard deviation: 58.5 ± 5.52 years). Whole-brain analysis revealed specific microstructural alterations between patients and healthy controls matched for age, sex, handedness, and cognitive status congruent with the literature and known Parkinson’s disease pathology. A general linear model revealed distinct microstructural alterations associated with poor bimanual coordination in Parkinson’s disease, corrected for multiple comparisons using a permutation-based approach. Integrating known functional topography, we conclude that distinct changes in microstructure cause an impediment of structures involved in attention, working memory, executive function, motor planning, motor control, and visual processing contributing to impaired bimanual coordination in Parkinson’s disease.

Coordination of voice, hands and feet in rhythm and beat performance

Interlimb coordination is critical to the successful performance of simple activities in everyday life and it depends on precisely timed perception–action coupling. This is particularly true in music-making, where performers often use body-movements to keep the beat while playing more complex rhythmic patterns. In the current study, we used a musical rhythmic paradigm of simultaneous rhythm/beat performance to examine how interlimb coordination between voice, hands and feet is influenced by the inherent figure-ground relationship between rhythm and beat. Sixty right-handed participants—professional musicians, amateur musicians and non-musicians—performed three short rhythmic patterns while keeping the underlying beat, using 12 different combinations of voice, hands and feet. Results revealed a bodily hierarchy with five levels (1) left foot, (2) right foot, (3) left hand, (4) right hand, (5) voice, i.e., more precise task execution was observed when the rhythm was performed with an effector occupying a higher level in the hierarchy than the effector keeping the beat. The notion of a bodily hierarchy implies that the role assigned to the different effectors is key to successful interlimb coordination: the performance level of a specific effector combination differs considerably, depending on which effector holds the supporting role of the beat and which effector holds the conducting role of the rhythm. Although performance generally increased with expertise, the evidence of the hierarchy was consistent in all three expertise groups. The effects of expertise further highlight how perception influences action. We discuss the possibility that musicians’ more robust metrical prediction models make it easier for musicians to attenuate prediction errors than non-musicians. Overall, the study suggests a comprehensive bodily hierarchy, showing how interlimb coordination is influenced by hierarchical principles in both perception and action.

A TMS-induced cortical silent period delays the contralateral limb for bimanual symmetrical movements and the reaction time delay is reduced on startle trials

Bimanual actions are typically initiated and executed in a temporally synchronous manner, likely due to planning bilateral commands as a single motor "program." Applying high intensity transcranial magnetic stimulation (TMS) to the motor cortex can result in a contralateral cortical silent period that delays reaction time (RT), if timed to coincide with the final motor output stage. The current study examined the impact of a unilateral TMS silent period on the RT and inter-limb timing of bilateral wrist extension. In addition, because a loud, startling acoustic stimulus (SAS) can result in the involuntary release of pre-programmed actions via increased reticulospinal activation, it was of interest whether startle-induced speeding of response initiation would moderate the impact of the TMS-induced RT delay. Participants performed blocks of unilateral and bilateral wrist extension in response to an acoustic (82dB) go-signal. On selected trials, either TMS was applied to the left motor cortex 70 ms prior to the expected EMG response onset, a SAS (120dB) replaced the go-signal, or both TMS and SAS were delivered. Results showed that TMS led to a significant RT delay in the right limb during both unimanual and bimanual extension but had no impact on the left limb initiation. In addition, the magnitude of the right limb RT delay was smaller when the response was triggered by a SAS. These results imply that preplanned bimanually synchronous movements are susceptible to lateralized dissociation late into the cortical motor output stage and movements triggered by startle involve increased reticulospinal output.

Correlations between Hand Dexterity and Bimanual Coordination on the Activities of Daily Living in Older Adults with Mild Cognitive Impairment

Background/Aims

Many motor impairments are present in older adults with cognitive decline. One of them is the impairment of hand dexterity and bimanual coordination that result in poor functional ability in the activities of daily living (ADL). This study investigated the effects of hand dexterity and bimanual coordination declination on the sub-domains of ADL in older adults with mild cognitive impairment (MCI).

Methods

Thirty-one senior individuals with MCI were recruited in this study. The Purdue Pegboard Test was used to measure hand dexterity, and bimanual coordination was assessed by the continuous circle-drawing task. Their ADL were assessed with the General Activity Daily Living questionnaire.

Results

The correlations analysis showed an association between the dominant hand and bimanual dexterity with the domestic domain of ADL and all conditions of hand dexterity with the complex domain of ADL. Moreover, the multiple regression analysis showed that the predictor of the greatest effect for domestic and complex domains was dominant hand dexterity.

Discussion/Conclusion

These results revealed that dominant hand dexterity strongly affected domestic and complex ADL in older adults with MCI. There were age-related changes regarding lateral asymmetrical motor reduction, especially in cognitive tasks. However, complex tasks involving cognitive function may need dominant, nondominant and bimanual hand dexterity.

Unimanual sensorimotor learning-A simultaneous EEG-fMRI aging study

Sensorimotor coordination requires orchestrated network activity in the brain, mediated by inter‐ and intra‐hemispheric interactions that may be affected by aging‐related changes. We adopted a theoretical model, according to which intra‐hemispheric inhibition from premotor to primary motor cortex is mandatory to compensate for inter‐hemispheric excitation through the corpus callosum. To test this as a function of age we acquired electroencephalography (EEG) simultaneously with functional magnetic resonance imaging (fMRI) in two groups of healthy adults (younger N = 13: 20–25 year and older N = 14: 59–70 year) while learning a unimanual motor task. On average, quality of performance of older participants stayed significantly below that of the younger ones. Accompanying decreases in motor‐event‐related EEG β‐activity were lateralized toward contralateral motor regions, albeit more so in younger participants. In this younger group, the mean β‐power during motor task execution was significantly higher in bilateral premotor areas compared to the older adults. In both groups, fMRI blood oxygen level dependent (BOLD) signals were positively correlated with source‐reconstructed β‐amplitudes: positive in primary motor and negative in premotor cortex. This suggests that β‐amplitude modulation is associated with primary motor cortex “activation” (positive BOLD response) and premotor “deactivation” (negative BOLD response). Although the latter results did not discriminate between age groups, they underscore that enhanced modulation in primary motor cortex may be explained by a β‐associated excitatory crosstalk between hemispheres.

Representational Similarity Scores of Digits in the Sensorimotor Cortex Are Associated with Behavioral Performance

Previous studies aimed to unravel a digit-specific somatotopy in the primary sensorimotor (SM1) cortex. However, it remains unknown whether digit somatotopy is associated with motor preparation and/or motor execution during different types of tasks. We adopted multivariate representational similarity analysis to explore digit activation patterns in response to a finger tapping task (FTT). Sixteen healthy young adults underwent magnetic resonance imaging, and additionally performed an out-of-scanner choice reaction time task (CRTT) to assess digit selection performance. During both the FTT and CRTT, force data of all digits were acquired using force transducers. This allowed us to assess execution-related interference (i.e., digit enslavement; obtained from FTT & CRTT), as well as planning-related interference (i.e., digit selection deficit; obtained from CRTT) and determine their correlation with digit representational similarity scores of SM1. Findings revealed that digit enslavement during FTT was associated with contralateral SM1 representational similarity scores. During the CRTT, digit enslavement of both hands was also associated with representational similarity scores of the contralateral SM1. In addition, right hand digit selection performance was associated with representational similarity scores of left S1. In conclusion, we demonstrate a cortical origin of digit enslavement, and uniquely reveal that digit selection is associated with digit representations in primary somatosensory cortex (S1). Significance statement In current systems neuroscience, it is of critical importance to understand the relationship between brain function and behavioral outcome. With the present work, we contribute significantly to this understanding by uniquely assessing how digit representations in the sensorimotor cortex are associated with planning- and execution-related digit interference during a continuous finger tapping and a choice reaction time task. We observe that digit enslavement (i.e., execution-related interference) finds its origin in contralateral digit representations of SM1, and that deficits in digit selection (i.e., planning-related interference) in the right hand during a choice reaction time task are associated with more overlapping digit representations in left S1. This knowledge sheds new light on the functional contribution of the sensorimotor cortex to everyday motor skills.

The Influence of Altered-Gravity on Bimanual Coordination: Retention and Transfer

Many of the activities associated with spaceflight require individuals to coordinate actions between the limbs (e.g., controlling a rover, landing a spacecraft). However, research investigating the influence of gravity on bimanual coordination has been limited. The current experiment was designed to determine an individual's ability to adapt to altered-gravity when performing a complex bimanual force coordination task, and to identify constraints that influence coordination dynamics in altered-gravity. A tilt table was used to simulate gravity on Earth [90° head-up tilt (HUT)] and microgravity [6° head-down tilt (HDT)]. Right limb dominant participants (N = 12) were required to produce 1:1 in-phase and 1:2 multi-frequency force patterns. Lissajous information was provided to guide performance. Participants performed 14, 20 s trials at 90° HUT (Earth). Following a 30-min rest period, participants performed, for each coordination pattern, two retention trials (Earth) followed by two transfer trials in simulated microgravity (6° HDT). Results indicated that participants were able to transfer their training performance during the Earth condition to the microgravity condition with no additional training. No differences between gravity conditions for measures associated with timing (interpeak interval ratio, phase angle slope ratio) were observed. However, despite the effective timing of the force pulses, there were differences in measures associated with force production (peak force, STD of peak force mean force). The results of this study suggest that Lissajous displays may help counteract manual control decrements observed during microgravity. Future work should continue to explore constraints that can facilitate or interfere with bimanual control performance in altered-gravity environments.

Individual Optimal Attentional Strategy in Motor Learning Tasks Characterized by Steady-State Somatosensory and Visual Evoked Potentials

Focus of attention is one of the most influential factors facilitating motor performance. Previous evidence supports that the external focus (EF) strategy, which directs attention to movement outcomes, is associated with better motor performance than the internal focus (IF) strategy, which directs attention to body movements. However, recent studies have reported that the EF strategy is not effective for some individuals. Furthermore, neuroimaging studies have demonstrated that the frontal and parietal areas characterize individual optimal attentional strategies for motor tasks. However, whether the sensory cortices are also functionally related to individual optimal attentional strategy remains unclear. Therefore, the present study examined whether an individual’s sensory processing ability would reflect the optimal attentional strategy. To address this point, we explored the relationship between responses in the early sensory cortex and individuals’ optimal attentional strategy by recording steady-state somatosensory evoked potentials (SSSEP) and steady-state visual evoked potentials (SSVEP). Twenty-six healthy young participants first performed a motor learning task with reaching movements under IF and EF conditions. Of the total sample, 12 individuals showed higher after-effects under the IF condition than the EF condition (IF-dominant group), whereas the remaining individuals showed the opposite trend (EF-dominant group). Subsequently, we measured SSSEP from bilateral primary somatosensory cortices while presenting vibrotactile stimuli and measured SSVEP from bilateral primary visual cortices while presenting checkerboard visual stimuli. The degree of increasing SSSEP response when the individuals in the IF-dominant group directed attention to vibrotactile stimuli was significantly more potent than those in the EF-dominant individuals. By contrast, the individuals in the EF-dominant group showed a significantly larger SSVEP increase while they directed attention to visual stimuli compared with the IF-dominant individuals. Furthermore, a significant correlation was observed such that individuals with more robust IF dominance showed more pronounced SSSEP attention modulation. These results suggest that the early sensory areas have crucial brain dynamics to characterize an individual’s optimal attentional strategy during motor tasks. The response characteristics may reflect the individual sensory processing ability, such as control of priority to the sensory inputs. Considering individual cognitive traits based on the suitable attentional strategy could enhance adaptability in motor tasks.

A brief review of motor imagery and bimanual coordination

Motor imagery is increasingly being used in clinical settings, such as in neurorehabilitation and brain computer interface (BCI). In stroke, patients lose upper limb function and must re-learn bimanual coordination skills necessary for the activities of daily living. Physiotherapists integrate motor imagery with physical rehabilitation to accelerate recovery. In BCIs, users are often asked to imagine a movement, often with sparse instructions. The EEG pattern that coincides with this cognitive task is captured, then used to execute an external command, such as operating a neuroprosthetic device. As such, BCIs are dependent on the efficient and reliable interpretation of motor imagery. While motor imagery improves patient outcome and informs BCI research, the cognitive and neurophysiological mechanisms which underlie it are not clear. Certain types of motor imagery techniques are more effective than others. For instance, focusing on kinesthetic cues and adopting a first-person perspective are more effective than focusing on visual cues and adopting a third-person perspective. As motor imagery becomes more dominant in neurorehabilitation and BCIs, it is important to elucidate what makes these techniques effective. The purpose of this review is to examine the research to date that focuses on both motor imagery and bimanual coordination. An assessment of current research on these two themes may serve as a useful platform for scientists and clinicians seeking to use motor imagery to help improve bimanual coordination, either through augmenting physical therapy or developing more effective BCIs.