Deficits In Bimanual Coordination Research Articles

Distinctive features of bimanual coordination in idiopathic normal pressure hydrocephalus

BackgroundIdiopathic normal pressure hydrocephalus (iNPH) is characterized by cerebrospinal fluid circulation disorders, and presents as gait and balance disturbances similar to those observed in other incurable neurological diseases. Although previous studies have reported deficits in bimanual coordination among patients with iNPH, these potential pathological characteristics have not received much attention to date. This study investigated the temporal characteristics of a bimanual finger-tapping task in patients with iNPH, focusing on within- and between-hand coordination.MethodsStudy participants comprised three groups: patients with iNPH (N = 19, mean age = 76.9 ± 5.6 years), older adults (N = 19, 76.4 ± 5.3 years), and younger adults (N = 13, 32.2 ± 8.5 years). Participants performed a bimanual finger-tapping task under five conditions that manipulated the temporal differences between the two taps.ResultsThe iNPH group exhibited significantly greater errors in both within- and between-hand coordination tasks compared to the other two groups.ConclusionThese results suggest that assessing temporal errors in bimanual coordination tasks, particularly within-hand coordination, may be useful for uncovering pathological characteristics specific to iNPH.

In-depth quantification of bimanual coordination using the Kinarm exoskeleton robot in children with unilateral cerebral palsy

BackgroundRobots have been proposed as tools to measure bimanual coordination in children with unilateral cerebral palsy (uCP). However, previous research only examined one task and clinical interpretation remains challenging due to the large amount of generated data. This cross-sectional study aims to examine bimanual coordination by using multiple bimanual robotics tasks in children with uCP, and their relation to task execution and unimanual performance.MethodsThe Kinarm exoskeleton robot was used in 50 children with uCP (mean age: 11 years 11 months ± 2 years 10 months, Manual Ability Classification system (MACS-levels: l = 27, ll = 16, lll = 7)) and 50 individually matched typically developing children (TDC). All participants performed three tasks: object-hit (hit falling balls), ball-on-bar (balance a ball on a bar while moving to a target) and circuit task (move a cursor along a circuit by making horizontal and vertical motions with their right and left hand, respectively). Bimanual parameters provided information about bimanual coupling and interlimb differences. Differences between groups and MACS-levels were investigated using ANCOVA with age as covariate (α < 0.05, {upeta }_{p}^{2}). Correlation analysis (r) linked bimanual coordination to task execution and unimanual parameters.ResultsChildren with uCP exhibited worse bimanual coordination compared to TDC in all tasks (p ≤ 0.05, {eta }_{p}^{2} = 0.05–0.34). The ball-on-bar task displayed high effect size differences between groups in both bimanual coupling and interlimb differences (p < 0.001, {eta }_{p}^{2} = 0.18–0.36), while the object-hit task exhibited variations in interlimb differences (p < 0.001, {eta }_{p}^{2} = 0.22–0.34) and the circuit task in bimanual coupling (p < 0.001, {eta }_{p}^{2} = 0.31). Mainly the performance of the ball-on-bar task (p < 0.05, {eta }_{p}^{2} = 0.18–0.51) was modulated by MACS-levels, showing that children with MACS-level lll had worse bimanual coordination compared to children with MACS-level l and/or II. Ball-on-bar outcomes were highly related to task execution (r = − 0.75–0.70), whereas more interlimb differences of the object-hit task were moderately associated with a worse performance of the non-dominant hand (r = − 0.69–(− 0.53)).ConclusionThis study gained first insight in important robotic tasks and outcome measures to quantify bimanual coordination deficits in children with uCP. The ball-on-bar task showed the most discriminative ability for both bimanual coupling and interlimb differences, while the object-hit and circuit tasks are unique to interlimb differences and bimanual coupling, respectively.

Development and Psychometric Testing of the Bimanual Assessment Measure for People With Chronic Stroke.

Few tools are available to assess bimanual deficits after stroke. To develop the Bimanual Assessment Measure (BAM), which assesses a person's hand coordination in both preferred and prestroke roles (i.e., stabilizer or manipulator). Development and psychometric testing of the BAM. Research laboratory. People with chronic stroke (n = 24), age-matched controls (n = 23), and occupational therapists (n = 40). We assessed the BAM's internal consistency, reliability, and face and known-groups validity. Items were selected as meaningful tasks that represented a range of bimanual coordination requirements (e.g., symmetrical forces and timing, asymmetrical forces and timing, time-limited reactive movement). Focus groups of people with stroke and occupational therapists provided input into BAM development. The BAM was found to have excellent reliability and internal consistency and face and known-groups validity. The BAM is a valid, reliable measure for people with chronic stroke that identifies bimanual coordination deficits beyond unimanual impairments and the potential capacity for people to return to prestroke hand roles (i.e., as a manipulator). What This Article Adds: This article introduces the BAM as a new assessment measure of bimanual functioning with the potential capacity to restore prestroke hand roles as either a manipulator or a stabilizer among people with chronic stroke.

Bimanual coordination deficits in hands following stroke and their relationship with motor and functional performance

BackgroundStroke can lead to movement disorders that affect interlimb coordination control of the bilateral upper extremities, especially the hands. However, few studies have investigated the influence of a stroke on bimanual force coordination control between the hands using a quantitative measurement tool, or the relationship of force coordination with paretic upper extremity motor and functional performance. We aimed to investigate these outcomes using a novel measurement device, and analyze the relationship of bimanual force coordination control deficits in both hands with motor and functional performances of the paretic upper extremity in stroke patients.MethodsSixteen healthy adults and 22 stroke patients were enrolled. A novel bilateral hand grip measurement device with two embedded dynamometers was used to evaluate the grip force during a bilateral hand grip-force coordination control task. The alternating time and force applied for coordination with the grip force of both hands were calculated to analyze control of bimanual grip force coordination. Motor and functional measurements included the upper-extremity portion of the Fugl-Meyer assessment (FMA-UE), Wolf Motor Function Test (WMFT), Motor Assessment Scale (MAS), and Barthel Index (BI).ResultsCompared with the healthy group, the alternating time from the non-paretic to the paretic hand was 27.6% shorter for stroke patients (p < 0.001). The grip force generated for coordination in the healthy group was significantly greater (30–59%) than that of the stroke group (p < 0.05), and the coefficients of variation of alternating time (p = 0.001) and force applied (p = 0.002) were significantly higher in the stroke group than the healthy group. The alternating time from the paretic to the non-paretic hand showed moderately significant correlations with the FMA-UE (r = − 0.533; p = 0.011), the WMFT (r = − 0.450; p = 0.036), and the BI (r = − 0.497; p = 0.019).ConclusionsStroke results in a decline in bimanual grip force generation and increases the alternating time for coordinating the two hands. A shorter alternating time is moderately to highly associated with enhanced motor and functional performances.

Age-Related Changes in Bimanual Instrument Playing with Rhythmic Cueing.

Deficits in bimanual coordination of older adults have been demonstrated to significantly limit their functioning in daily life. As a bimanual sensorimotor task, instrument playing has great potential for motor and cognitive training in advanced age. While the process of matching a person’s repetitive movements to auditory rhythmic cueing during instrument playing was documented to involve motor and attentional control, investigation into whether the level of cognitive functioning influences the ability to rhythmically coordinate movement to an external beat in older populations is relatively limited. Therefore, the current study aimed to examine how timing accuracy during bimanual instrument playing with rhythmic cueing differed depending on the degree of participants’ cognitive aging. Twenty one young adults, 20 healthy older adults, and 17 older adults with mild dementia participated in this study. Each participant tapped an electronic drum in time to the rhythmic cueing provided using both hands simultaneously and in alternation. During bimanual instrument playing with rhythmic cueing, mean and variability of synchronization errors were measured and compared across the groups and the tempo of cueing during each type of tapping task. Correlations of such timing parameters with cognitive measures were also analyzed. The results showed that the group factor resulted in significant differences in the synchronization errors-related parameters. During bimanual tapping tasks, cognitive decline resulted in differences in synchronization errors between younger adults and older adults with mild dimentia. Also, in terms of variability of synchronization errors, younger adults showed significant differences in maintaining timing performance from older adults with and without mild dementia, which may be attributed to decreased processing time for bimanual coordination due to aging. Significant correlations were observed between variability of synchronization errors and performance of cognitive tasks involving executive control and cognitive flexibility when asked for bimanual coordination in response to external timing cues at adjusted tempi. Also, significant correlations with cognitive measures were more prevalent in variability of synchronization errors during alternative tapping compared to simultaneous tapping. The current study supports that bimanual tapping may be predictive of cognitive processing of older adults. Also, tempo and type of movement required for instrument playing both involve cognitive and motor loads at different levels, and such variables could be important factors for determining the complexity of the task and the involved task requirements for interventions using instrument playing.

Bimanual coordination: A missing piece of arm rehabilitation after stroke.

Inability to use the arm in daily actions significantly lowers quality of life after stroke. Most contemporary post-stroke arm rehabilitation strategies that aspire to re-engage the weaker arm in functional activities have been greatly limited in their effectiveness. Most actions of daily life engage the two arms in a highly coordinated manner. In contrast, most rehabilitation approaches predominantly focus on restitution of the impairments and unilateral practice of the weaker hand alone. We present a perspective that this misalignment between real world requirements and intervention strategies may limit the transfer of unimanual capability to spontaneous arm use and functional recovery. We propose that if improving spontaneous engagement and use of the weaker arm in real life is the goal, arm rehabilitation research and treatment need to address the coordinated interaction between arms in targeted theory-guided interventions. Current narrow focus on unimanual deficits alone, difficulty in quantifying bimanual coordination in real-world actions and limited theory-guided focus on control and remediation of different coordination modes are some of the biggest obstacles to successful implementation of effective interventions to improve bimanual coordination in the real world. We present a theory-guided taxonomy of bimanual actions that will facilitate quantification of coordination for different real-world tasks and provide treatment targets for addressing coordination deficits. We then present evidence in the literature that points to bimanual coordination deficits in stroke survivors and demonstrate how current rehabilitation approaches are limited in their impact on bimanual coordination. Importantly, we suggest theory-based areas of future investigation that may assist quantification, identification of neural mechanisms and scientifically-based training/remediation approaches for bimanual coordination deficits post-stroke. Advancing the science and practice of arm rehabilitation to incorporate bimanual coordination will lead to a more complete functional recovery of the weaker arm, thus improving the effectiveness of rehabilitation interventions and augmenting quality of life after stroke.

Subthalamic deep brain stimulation and dopaminergic medication in Parkinson’s disease: Impact on inter-limb coupling

Patients with Parkinson’s disease (PD) often present with bimanual coordination deficits whose exact origins remain unclear. One aspect of bimanual coordination is inter-limb coupling. This is characterized by the harmonization of movement parameters between limbs. We assessed different aspects of bimanual coordination in patients with PD, including inter-limb coupling, and determined whether they are altered by subthalamic (STN) deep brain stimulation (DBS) or dopaminergic medication. Twenty PD patients were tested before STN DBS surgery; with and without medication. Post- surgery, patients were tested with their stimulators on and off as well as with and without medication. Patients were asked to perform a unimanual and bimanual rapid repetitive diadochokinesis task. The difference in mean amplitude and mean duration of cycles between hands was computed in order to assess inter-limb coupling. Also, mean angular velocity of both hands and structural coupling were computed for the bimanual task. There was a positive effect of medication and stimulation on mean angular velocity, which relates to clinical improvement. PD patients exhibited temporal inter-limb coupling that was not altered by either medication or STN stimulation. However, PD patients did not exhibit spatial inter-limb coupling. Again, this was not altered by medication or stimulation. Collectively, the results suggest that structures independent of the dopaminergic system and basal ganglia may mediate temporal and spatial inter-limb coupling.

Movement preparation and execution: differential functional activation patterns after traumatic brain injury.

Years following the insult, patients with traumatic brain injury often experience persistent motor control problems, including bimanual coordination deficits. Previous studies revealed that such deficits are related to brain structural white and grey matter abnormalities. Here, we assessed, for the first time, cerebral functional activation patterns during bimanual movement preparation and performance in patients with traumatic brain injury, using functional magnetic resonance imaging. Eighteen patients with moderate-to-severe traumatic brain injury (10 females; aged 26.3 years, standard deviation = 5.2; age range: 18.4-34.6 years) and 26 healthy young adults (15 females; aged 23.6 years, standard deviation = 3.8; age range: 19.5-33 years) performed a complex bimanual tracking task, divided into a preparation (2 s) and execution (9 s) phase, and executed either in the presence or absence of augmented visual feedback. Performance on the bimanual tracking task, expressed as the average target error, was impaired for patients as compared to controls (P < 0.001) and for trials in the absence as compared to the presence of augmented visual feedback (P < 0.001). At the cerebral level, movement preparation was characterized by reduced neural activation in the patient group relative to the control group in frontal (bilateral superior frontal gyrus, right dorsolateral prefrontal cortex), parietal (left inferior parietal lobe) and occipital (right striate and extrastriate visual cortex) areas (P's < 0.05). During the execution phase, however, the opposite pattern emerged, i.e. traumatic brain injury patients showed enhanced activations compared with controls in frontal (left dorsolateral prefrontal cortex, left lateral anterior prefrontal cortex, and left orbitofrontal cortex), parietal (bilateral inferior parietal lobe, bilateral superior parietal lobe, right precuneus, right primary somatosensory cortex), occipital (right striate and extrastriate visual cortices), and subcortical (left cerebellum crus II) areas (P's < 0.05). Moreover, a significant interaction effect between Feedback Condition and Group in the primary motor area (bilaterally) (P < 0.001), the cerebellum (left) (P < 0.001) and caudate (left) (P < 0.05), revealed that controls showed less overlap of activation patterns accompanying the two feedback conditions than patients with traumatic brain injury (i.e. decreased neural differentiation). In sum, our findings point towards poorer predictive control in traumatic brain injury patients in comparison to controls. Moreover, irrespective of the feedback condition, overactivations were observed in traumatically brain injured patients during movement execution, pointing to more controlled processing of motor task performance.

Task-Dependent Bimanual Coordination After Stroke: Relationship With Sensorimotor Impairments

ObjectivesTo determine (1) bimanual coordination deficits in patients with stroke using 3-dimensional kinematic analyses as they perform naturalistic tasks requiring collaborative interaction of the 2 arms; and (2) whether bimanual coordination deficits are related to clinical measures of sensorimotor impairments and unimanual performance of the paretic arm. DesignCase-control study. SettingRehabilitation hospital research institute. ParticipantsParticipants (N=24) were patients with unilateral chronic stroke (n=14) and age-matched controls (n=10). InterventionsNot applicable. Main Outcome MeasuresTemporal coordination between the 2 hands as participants performed (1) a symmetric task: reach to pick up a box using both hands; and (2) an asymmetric task: open a drawer with 1 hand to press a button inside with the other hand. ResultsDuring the symmetric task, patients and controls showed preserved temporal coupling while transporting the hands to the box. However, on reaching the box, patients demonstrated an impaired ability to cooperatively interact their 2 arms for an efficient pickup. This led to significantly longer pickup times compared with controls. Pickup time positively correlated with proprioceptive deficits of the paretic arm. During the asymmetric task, patients had a longer time delay between drawer opening and button pressing movements than controls. The deficits in asymmetric coordination did not significantly correlate with sensorimotor impairments or unimanual paretic arm performance. ConclusionsBimanual coordination was impaired in patients poststroke during symmetric and asymmetric bimanual tasks that required cooperative interaction between the 2 arms. While the proprioceptive system contributes to symmetric cooperative coordination, commonly tested measures of paretic arm impairment or performance, or both, do not strongly predict deficits in bimanual coordination.

Age-related motor dysfunction: Manual slowing in Gorilla gorilla gorilla.

Aging in humans and rhesus monkeys is commonly associated with motor function decrements including dexterity, speed, and strength. Despite their longevity and phylogenetic relatedness to humans, the effects of aging on motor function in non-human apes have been minimally studied. We conducted two experiments with western lowland gorillas (11-54 years of age) to determine whether aged gorillas exhibit motor deficits similar to those seen in other species. In experiment one, gorillas extracted up to 12 food rewards lodged in holes of a Lexan board. Extraction rates were calculated for eight test sessions. A repeated measures ANOVA revealed no main effects of session or sex on extraction rate, but a significant main effect of age. Comparisons between the first and last sessions showed that experience significantly improved extraction rates in young but not aged gorillas. In experiment two, gorillas retrieved a hex nut from three differently shaped rods with each hand for a reward. Latencies of retrieval were calculated for 16 test sessions. A repeated measures ANOVA revealed significant main effects of age class, sex, and session. There were significant interactions between session and sex, session and age, and session, sex, and age. These findings held when analyzing each rod shape separately. Post hoc comparisons revealed that young gorillas were significantly faster at the task than aged gorillas, and females were faster than males. This finding held only for the question mark shaped rod when analyzing each rod shape separately. Comparisons between the first and last sessions showed that experience did not significantly improve latencies in either age or sex class. The direction of these results are congruent with previous findings in humans and monkeys and suggest that aged gorillas experience deficits in bimanual coordination compared to younger gorillas and that age and sex influence fine motor ability in gorillas.

Inter-limb coupling during diadochokinesis in Parkinson's and Huntington's disease

Patients with neurodegenerative diseases often exhibit deficits in bimanual coordination. One characteristic of bimanual movements is inter-limb coupling. It is the property of motor performance harmonization between hands during a bimanual task. The objective of this study was to identify whether spatial and temporal inter-limb coupling occurred in Parkinson's disease (PD) and Huntington's disease (HD) patients. Twenty-three PD patients and 15 healthy controls were tested. Data from 12 choreic HD patients were also taken from a databank. Participants were asked to perform a unimanual and bimanual rapid repetitive diadochokinesis task. The difference between hands in mean amplitude and mean duration of cycles was computed in the unimanual and bimanual tasks for each group. Results show that healthy controls exhibited temporal and spatial inter-limb coupling during the bimanual diadochokinesis task. Conversely, PD and HD patients exhibited temporal inter-limb coupling; but failed to exhibit spatial inter-limb coupling during the bimanual diadochokinesis task. Furthermore, HD patients exhibited reduced levels of structural coupling compared to controls and PD patients. These results suggest that alterations in basal ganglia-thalamo-cortical networks due to PD and HD do not affect temporal inter-limb coupling. However, common pathophysiological changes related to PD and HD may cause altered spatial inter-limb coupling during a rapid repetitive bimanual diadochokinesis task.

Is DOPA-Responsive Hypokinesia Responsible for Bimanual Coordination Deficits in Parkinson’s Disease?

Bradykinesia is a well-documented DOPA-responsive clinical feature of Parkinson’s disease (PD). While amplitude deficits (hypokinesia) are a key component of this slowness, it is important to consider how dopamine influences both the amplitude (hypokinesia) and frequency components of bradykinesia when a bimanually coordinated movement is required. Based on the notion that the basal ganglia are associated with sensory deficits, the influence of dopaminergic replacement on sensory feedback conditions during bimanual coordination was also evaluated. Bimanual movements were examined in PD and healthy comparisons in an unconstrained three-dimensional coordination task. PD were tested “off” (overnight withdrawal of dopaminergic treatment) and “on” (peak dose of dopaminergic treatment), while the healthy group was evaluated for practice effects across two sessions. Required cycle frequency (increased within each trial from 0.75 to 2 Hz), type of visual feedback (no vision, normal vision, and augmented vision), and coordination pattern (symmetrical in-phase and non-symmetrical anti-phase) were all manipulated. Overall, coordination (mean accuracy and standard deviation of relative phase) and amplitude deficits during bimanual coordination were confirmed in PD participants. In addition, significant correlations were identified between severity of motor symptoms as well as bradykinesia to greater coordination deficits (accuracy and stability) in PD “off” group. However, even though amplitude deficits (hypokinesia) improved with dopaminergic replacement, it did not improve bimanual coordination performance (accuracy or stability) in PD patients from “off” to “on.” Interestingly, while coordination performance in both groups suffered in the augmented vision condition, the amplitude of the more affected limb of PD was notably influenced. It can be concluded that DOPA-responsive hypokinesia contributes to, but is not directly responsible for bimanual coordination impairments in PD. It is likely that bimanual coordination deficits in PD are caused by the combination of dopaminergic system dysfunction as well as other neural impairments that may be DOPA-resistant or related to non-dopaminergic pathways.

Bimanual motor coordination in agenesis of the corpus callosum.

The nature and extent of deficiencies in bimanual motor coordination in individuals with agenesis of the corpus callosum (ACC) was studied using the computerized Bimanual Coordination Test (cBCT). Compared with previous bimanual tasks, the cBCT is more specifically reliant on interhemispheric interactions of lateralized motor control, allows more precise measurement, and permits examination of performance over a wider range of bimanual challenges. The cBCT performance of 13 high-functioning individuals with complete ACC was compared to 21 age- and IQ-matched controls. The groups did not differ in unimanual response speed. On trials involving angled paths that require bimanual coordination, the ACC group performed significantly slower and less accurately across all angles. The largest group differences in speed occurred on trials where the hands must respond symmetrically, while mirror-image (vs. parallel) responding produced the greatest deficits in accuracy. These data confirm previous findings of deficits in bimanual coordination in callosal absence, but using significantly improved measurement technology. Deficits in bimanual coordination in ACC are present across different demands for interhand interactions in the speed and direction of movement.

Bimanual coordination deficits with Parkinson's disease: the influence of movement speed and external cueing.

Continuous coordinated movement of the upper limbs performed at different movement frequencies, and with different external timing conditions, was examined in individuals with Parkinson's disease (PD) and healthy, age- and gender-matched controls. Participants performed symmetric in-phase movements toward and away from the midline of the body, and isodirectional anti-phase movements at one of three metronome speeds (0.75, 1.25, and 1.75 Hz), and in two different auditory cueing conditions (cue present, cue absent). Measures of relative phase accuracy (absolute mean error) and stability (standard deviation) revealed that individuals with PD performed in-phase movements as well as the controls, while anti-phase movements were performed with greater mean error and variability. The adverse effects of PD on the anti-phase task were also reflected by freezing (8.1% of anti-phase trials) and hypometric deficits (5.1% of anti-phase trials) during movement. None of these PD-related impairments occurred during in-phase trials. The overall accuracy or stability of movement coordination was not improved with the presence of external pacing cues, suggesting that although execution impairments of individuals with PD may be dramatically influenced by attention, external cueing does not necessarily improve movement performance.

Bimanual coordination deficits with Parkinson's disease: The influence of movement speed and external cueing

Continuous coordinated movement of the upper limbs performed at different movement frequencies, and with different external timing conditions, was examined in individuals with Parkinson's disease (PD) and healthy, age- and gender-matched controls. Participants performed symmetric in-phase movements toward and away from the midline of the body, and isodirectional anti-phase movements at one of three metronome speeds (0.75, 1.25, and 1.75 Hz), and in two different auditory cueing conditions (cue present, cue absent). Measures of relative phase accuracy (absolute mean error) and stability (standard deviation) revealed that individuals with PD performed in-phase movements as well as the controls, while anti-phase movements were performed with greater mean error and variability. The adverse effects of PD on the anti-phase task were also reflected by freezing (8.1% of anti-phase trials) and hypometric deficits (5.1% of anti-phase trials) during movement. None of these PD-related impairments occurred during in-phase trials. The overall accuracy or stability of movement coordination was not improved with the presence of external pacing cues, suggesting that although execution impairments of individuals with PD may be dramatically influenced by attention, external cueing does not necessarily improve movement performance. © 2002 Movement Disorder Society.

Speech-Motor Control and Interhemispheric Relations in Recovered and Persistent Stuttering

The neurological basis of stuttering is associated with anomalies of interhemispheric relations and of the neural mechanisms of speech-motor control, specifically those involving the supplementary motor area (SMA). Stuttering typically develops through childhood and adolescence but many children will recover without formal treatment or intervention. The hypothesis that such spontaneous recovery is related to a maturation of the SMA is explored. Four experimental tasks were performed by adults whose stuttering has persisted, adults who reported having stuttered as children, and a control group of adults who reported never having stuttered. A Sequence Reproduction Finger Tapping task (Webster, 1986) and a Bimanual Crank Turning task (Preilowski, 1972) examined the functioning of the SMA, and 2 Divided Visual Field tasks examined asymmetries of hemispheric activation. The overall pattern of results for persistent stutterers compared to nonstutterers was consistent with motor-perceptual anomalies previously reported in the literature. The Bimanual Crank Turning task revealed additionally that the bimanual coordination deficits reported in adults who stutter are kinesthetically based and mediated through anterior callosal systems, including the SMA. Ex-stutterers were similar to nonstutterers in their performance of the motor control tasks, but similar to persistent stutterers in perceptual asymmetries associated with Divided Visual Field tasks. Taken together, the results from the four experimental tasks support the general hypothesis that an anomaly in interhemispheric relations and a deficit in the mechanisms of speech-motor control are each a necessary but not sufficient condition for stuttering and that recovery from childhood stuttering reflects a maturation of the mechanisms of speech-motor control.

Who tells one hand what the other is doing: the neurophysiology of bimanual movements.

Research into neural mechanisms of bimanual coordination sheds light on questions raised by psychophysics. While the results we review are merely suggestive, the overall structure of the neural mechanisms may be emerging slowly.Different mechanisms may serve the spatial and temporal coupling of bimanual movements. Temporal coupling depends on a lateralized pace-keeping mechanism possibly associated with spinal CPGs, is preferentially controlled by the dominant hemisphere, and does not depend directly on the corpus callosum. Spatial coupling, in contrast, arises through interhemispheric interaction. Individual neurons in each hemisphere reflect this interaction, as does interhemispheric synchronization. The interaction allows decoupling of the arms, as substantiated by the PV analysis. Furthermore, bimanual proximal arm movements and finger movements are controlled differently, as shown in differences in the patterns of neural activity in M1 and SMA.Taken as a whole, the research we review has not yet culminated in a conclusive model. However, by combining psychophysics and neurophysiology, we raise concrete, testable hypotheses that may help realize this goal.*To whom correspondence should be addressed (e-mail: eilon@hbf.huji.ac.il).