Reacting while moving: influence of right limb movement on left limb reaction

An experiment was designed to determine whether the activation of a muscle group (flexors or extensors) used to produce an ongoing movement of one limb influenced the reaction time and associated initiation of elbow flexion or extension movements of the contralateral limb. Right-handed participants in the bimanual groups were asked to produce a pattern of flexion/extension movements defined by a sine wave (period = 2 s, amplitude = 16°) with the right limb. While performing the right limb movement, participants were instructed that they were to react as quickly as possible by making a flexion or extension movement with their left limb when the cursor they were using to track the sine wave changed color. Participants in the unimanual groups performed the left limb reaction time task but were not asked to make right limb movements. The reaction time stimulus occurred once in each trial and was presented at one of six locations on one of the six cycles comprising the sinusoidal waveform. Participants performed 7 blocks of 6 test trials. Reaction time was calculated as the time interval between the color change of the cursor and the initiation of the response with the left limb. Movement time was calculated as the interval of time between the initiation of the response and the left limb cursor crossing the upper or lower boundary line. Mean reaction of the left limb was significantly influenced by the concurrent type of movement (flexion/extension) of the right limb. Reaction times were shorter on trials in which both limbs were initiating movement with homologous muscles as compared to trials in which the limbs were initiating movement with non-homologous muscles. No differences were detected when the stimuli were presented during the ballistic phase of the right limb movement, and no differences at any position were detected for the unimanual groups. This result is consistent with the notion that neural crosstalk can influence the time required to react to a stimulus but this influence occurs when contralateral muscles are activated.     

Increasingly complex bimanual multi-frequency coordination patterns are equally easy to perform with on-line relative velocity feedback

An experiment was conducted to determine whether multi-frequency continuous bimanual circling movements of varying difficulty (1:2. 2:3, 3:4, and 4:5) could be effectively performed following relatively little practice when on-line continuous relative velocity feedback is provided. The between-subjects results indicate extremely effective bimanual multi-frequency performance for all coordination patterns with relatively stable and continuous movements of both limbs. The findings suggest that the previous performance effects using Lissajous feedback with reciprocal movement can be extended to circling movements using on-line relative velocity feedback. Contrary to the long-held position that these coordination patterns result in increasing difficulty, we failed to find systematic relative velocity error, variability, or bias differences between the participants performing the various multi-frequency coordination patterns. Indeed, coordination error, variability, and biases were remarkably low for each of the tasks. The results clearly indicate the ease with which participants are able to produce bimanual coordination patterns typically considered difficult if not impossible when salient visual information is provided that allows the participants to detect and correct their coordination errors.     

Impossible is nothing: 5:3 and 4:3 multi-frequency bimanual coordination

The present findings demonstrate that when participants are provided a Lissajous display with cursor indicating the position of the limbs and a template illustrating the desired movement pattern they can rapidly (10 min) and effectively (continuous relative phase errors and variability ~10°) tune in a difficult 5:3 bimanual coordination pattern and without additional practice re-tune their responding to an equally difficult 4:3 coordination pattern. The findings indicate the extreme difficulty associated with producing complex polyrhythms in previous experiments has been due to split attention when Lissajous feedback has been provided and inability of the participant to detect and correct coordination errors when only provided vision of the limbs. Effective transfer to the 4:3 polyrhythm without previous practice suggests that the perception–action system’s capabilities are extensive. The present findings when viewed in the context of recent experiments using similar protocols suggest that much, but not all, of the difficulty associated with producing a variety of bimanual coordination tasks should be viewed in terms of perceptual constraints imposed by the testing environment.     

Functional synchronization in repetitive bimanual prehension movements

To examine the mechanisms of functional bimanual synchronization in goal-directed movements, we studied the movement kinematics of motorically unimpaired subjects while they performed repetitive prehension movements (either unimanually or bimanually) to small food items. Compared to unimanual conditions, bimanual movement execution yielded a significantly prolonged mouth contact phase. We hypothesized that this threefold prolongation led to a proper functional synchronization of the movement onsets of both hands at the beginning of each new movement cycle. That these temporal adjustments occurred in the movement phase with maximal haptic input points to the importance of sensory feedback for bimanual coordination. These results are discussed with respect to the important role of sensory feedback in the timing of coordinated bimanual movements. Furthermore, we propose that time-based coordinating schemas, which are implemented by the cerebellum and the posterior parietal cortex using sensory feedback, underlie functional inter-limb coordination.     

Developmental changes in unimanual and bimanual aiming movements

The aim of this study was twofold: (a) analyze the development of reaction time (RT) and movement time (MT) for bimanual and unimanual movements and (b) investigate the interaction of age and sex on the changes in RT and MT. Participants (5-, 8-, and 11-year-olds) were asked to aim at target buttons under three conditions of movement: unimanual, bimanual symmetrical, and bimanual nonsymmetrical. As expected, RTs for bimanual symmetrical movements were shorter than RTs for unimanual and bimanual nonsymmetrical movements in the 5-year-olds. By the age of 8, bimanual nonsymmetrical movements still yielded longer RTs than unimanual and bimanual symmetrical movements, which no longer differed from each other. Regarding MT, in the 2 younger groups there was an advantage of unimanual over bimanual symmetrical movements. The latter were executed faster than nonsymmetrical movements at all ages. These results suggest that the evolution of RT and MT with age reflects development of interhemispheric transfer of information. It appears that the functional improvement of such transfer, which depends on the corpus callosum, progressively enables contralateral motor inhibition and the coordination of complex bilateral movements. The exchange of movement feedback information could mature more slowly than that of feed-forward information, explaining the extended time course of MT evolution.     

The coordination patterns observed when two hands reach-to-grasp separate objects

What determines coordination patterns when both hands reach to grasp separate objects at the same time? It is known that synchronous timing is preferred as the most stable mode of bimanual coordination. Nonetheless, normal unimanual prehension behaviour predicts asynchrony when the two hands reach towards unequal targets, with synchrony restricted to targets equal in size and distance. Additionally, sufficiently separated targets require sequential looking. Does synchrony occur in all cases because it is preferred in bimanual coordination or does asynchrony occur because of unimanual task constraints and the need for sequential looking? We investigated coordinative timing when participants (n = 8) moved their right (preferred) hand to the same object at a fixed distance but the left hand to objects of different width (3, 5, and 7 cm) and grip surface size (1, 2, and 3 cm) placed at different distances (20, 30, and 40 cm) over 270 randomised trials. The hand movements consisted of two components: (1) an initial component (IC) during which the hand reached towards the target while forming an appropriate grip aperture, stopping at (but not touching) the object; (2) a completion component (CC) during which the finger and thumb closed on the target. The two limbs started the IC together but did not interact until the deceleration phase when evidence of synchronisation began to appear. Nonetheless, asynchronous timing was present at the end of the IC and preserved through the CC even with equidistant targets. Thus, there was synchrony but requirements for visual information ultimately yielded asynchronous coordinative timing.     

Additional load decreases movement time in the wrist but not in arm movements at ID 6

An experiment using reciprocal arm and wrist aiming movements with an amplitude of 16^o and target width of .5° (ID = 6) was conducted to determine the impact of adding external loads. We predicted that wrist and arm performance may be differentially impacted by the added mass. Participants were asked to flex/extend their limb/lever in a horizontal plane at the wrist (arm stabilized) or elbow joint (wrist stabilized) in an attempt to move back and forth between the two targets as quickly and accurately as possible. External loads of 0, .568, or 1.136 kg were fixed at the distal end of the limb/lever. The targets and the current position of the limb were projected on the screen in front of the participant. The results indicated significant Group × Load interactions for movement time and percent time to peak velocity. Movement time decreased as load increased for the wrist but remained stable across loads for arm movements. Percent movement time utilized to accelerate the limb increased as load increased for wrist movements but only increased from 0 to .568 kg load for the arm movements. For both groups increased load had no significant effect on endpoint variability. The present findings suggest that the additional load allowed the control advantages of the wrist muscles to be exploited.     

Amplitude differences, spatial assimilation, and integrated feedback in bimanual coordination

The purpose of the experiment was to determine the influence of Lissajous feedback on 1:1 bimanual coordination patterns (0°, 90°, and 180° phase lags) when the movement amplitudes of the two limbs were different (30°, 60°). The present data supports the notion that the lead–lag relationship as well as amplitude assimilation observed in the literature can be partially attributed to the visual-perceptual factors present in the testing environment. When participants are provided integrated feedback in the form of Lissajous plots much of the lead–lag and amplitude assimilation effects were eliminated, and relative phase error and variability were also greatly reduced after only 3 min of practice under each condition.     

Perceptual and motor contributions to bimanual coordination

Following earlier work by Mechsner et al. (Nature 414 (2001) 69), the purpose of this experiment was to determine the perceptual and motoric contributions to bimanual coordination. Twenty right-handed, healthy, young adults performed continuous, horizontal, linear movements of both upper limbs at frequencies of 1.5 and 2.0 Hz. The goal was to control the spatial-temporal displacement of two flags by coordinating upper limb movements in two perceptual conditions. In a congruent condition, the movement of the flags matched the movement of the upper limbs. In an incongruent condition, the movement of the flags was opposite to the movement of the upper limbs. Measures of error in coordination provided support primarily for a motor view of bimanual coordination, and failed to replicate the earlier findings of Mechsner et al.     

Decomposition of spontaneous movements of infants as combinations of limb synergies

We hypothesized that a variety of limb movements in infants, including spontaneous movements and movements during interactions with the environment, can be represented as combinations of limb synergies, which are building blocks for generating coordinated movements of multiple limbs. A decomposition algorithm based on a nonnegative matrix factorization was applied to the discrete data segments taken from continuous data of limb movements in 298 infants (age, 3–4 months). The data were linearly decomposed into bases, which were referred to as synergies. The results showed that approximately 70 % of the variance in the velocity profiles of the data segments of the four limbs can be explained by a set of five simple synergies that represent single-limb movements and the synchronous movement of all limbs. The present method showed that the complex properties of limb movements can be represented as combinations of synergies. Furthermore, comparisons of movement patterns across different age groups showed that in older infants, the contribution ratios of each synergy were different between spontaneous movements and movements during playing with a toy, whereas in younger infants, there were no differences in the contribution ratios between the different movement conditions. These results demonstrate that decomposition into limb synergies is useful for determining the spatiotemporal properties of interlimb coordination during spontaneous movements and task-constrained movements in infants.     

Age-related changes in the bimanual advantage and in brain oscillatory activity during tapping movements suggest a decline in processing sensory reafference

Deficits in the processing of sensory reafferences have been suggested as accounting for age-related decline in motor coordination. Whether sensory reafferences are accurately processed can be assessed based on the bimanual advantage in tapping: because of tapping with an additional hand increases kinesthetic reafferences, bimanual tapping is characterized by a reduced inter-tap interval variability than unimanual tapping. A suppression of the bimanual advantage would thus indicate a deficit in sensory reafference. We tested whether elderly indeed show a reduced bimanual advantage by measuring unimanual (UM) and bimanual (BM) self-paced tapping performance in groups of young (n = 29) and old (n = 27) healthy adults. Electroencephalogram was recorded to assess the underlying patterns of oscillatory activity, a neurophysiological mechanism advanced to support the integration of sensory reafferences. Behaviorally, there was a significant interaction between the factors tapping condition and age group at the level of the inter-tap interval variability, driven by a lower variability in BM than UM tapping in the young, but not in the elderly group. This result indicates that in self-paced tapping, the bimanual advantage is absent in elderly. Electrophysiological results revealed an interaction between tapping condition and age group on low beta band (14–20 Hz) activity. Beta activity varied depending on the tapping condition in the elderly but not in the young group. Source estimations localized this effect within left superior parietal and left occipital areas. We interpret our results in terms of engagement of different mechanisms in the elderly depending on the tapping mode: a ‘kinesthetic’ mechanism for UM and a ‘visual imagery’ mechanism for BM tapping movement.     

Postural context alters the stability of bimanual coordination by modulating the crossed excitability of corticospinal pathways

The tendency for movements of the upper limbs to be drawn systematically toward one another and to follow similar spatiotemporal trajectories is well known. Although suppression of this tendency is integral to tasks of daily living, its exploitation may prove to be critical in the rehabilitation of acquired hemiplegias. In general, however, the task-related factors that determine the degree of coupling between the upper limbs and the mechanisms that mediate bilateral interactions between neural pathways projecting to the muscles of the arm and hand are not yet well understood. We present evidence that the postural context in which human participants perform upper limb movements determines the relative stability of patterns of bimanual coordination. Manipulation of the axes of rotation of forearm movements reversed the relative stability of simultaneous and alternating patterns of bimanual coordination. Transcranial magnetic stimulation of motor cortex revealed that these manipulations of postural context altered the crossed modulation of excitability in corticospinal pathways that arises from movement of the opposite limb. Furthermore, modulation of responses to electrical stimulation of the cervicomedullary junction indicated that crossed modulation was also expressed at the level of the spinal motoneurons. Our data support the view that crossed modulation of excitability in corticospinal pathways mediates the stability of bimanual coordination. Furthermore, task-related factors that are sufficient to give rise to changes in the stability of bimanual coordination are accompanied by crossed modulation of excitability at multiple levels of the neuraxis, indicative of a failure of inhibitory control.     

Resource-demanding versus cost-effective bimanual interaction in the brain

When two hands require different information in bimanual asymmetric movements, interference can occur via callosal connections and ipsilateral corticospinal pathways. This interference could potentially work as a cost-effective measure in symmetric movements, allowing the same information to be commonly available to both hands at once. Using functional magnetic resonance imaging, we investigated supra-additive and sub-additive neural interactions in bimanual movements during the initiation and continuation phases of movement. We compared activity during bimanual asymmetric and symmetric movements with the sum of activity during unimanual right and left finger-tapping. Supra-additive continuation-related activation was found in the right dorsal premotor cortex and left cerebellum (lobule V) during asymmetric movements. In addition, for unimanual movements, the right dorsal premotor cortex and left cerebellum (lobule V) showed significant activation only for left-hand (non-dominant) movements, but not for right-hand movements. These results suggest that resource-demanding interactions in bimanual asymmetric movements are involved in a non-dominant hand motor network that functions to keep non-dominant hand movements stable. We found sub-additive continuation-related activation in the supplementary motor area (SMA), bilateral cerebellum (lobule VI) in symmetric movements, and the SMA in asymmetric movements. This suggests that no extra demands were placed on these areas in bimanual movements despite the conventional notion that they play crucial roles in bimanual coordination. Sub-additive initiation-related activation in the left anterior putamen suggests that symmetric movements place lower demands on motor programming. These findings indicate that, depending on coordination patterns, the neural substrates of bimanual movements either exhibit greater effort to keep non-dominant hand movements stable, or save neural cost by sharing information commonly to both hands.     

Effect of transcranial magnetic stimulation on bimanual movements

Transcranial magnetic stimulation (TMS) of the motor cortex can interrupt voluntary contralateral rhythmic limb movements. Using the method of "resetting index" (RI), our study investigated the TMS effect on different types of bimanual movements. Six normal subjects participated. For unimanual movement, each subject tapped either the right or left index finger at a comfortable rate. For bimanual movement, index fingers of both hands tapped in the same (in-phase) direction or in the opposite (antiphase) direction. TMS was applied to each hemisphere separately at various intensities from 0.5 to 1.5 times motor threshold (MT). TMS interruption of rhythm was quantified by RI. For the unimanual movements, TMS disrupted both contralateral and ipsilateral rhythmic hand movements, although the effect was much less in the ipsilateral hand. For the bimanual in-phase task, TMS could simultaneously reset the rhythmic movements of both hands, but the effect on the contralateral hand was less and the effect on the ipsilateral hand was more compared with the unimanual tasks. Similar effects were seen from right and left hemisphere stimulation. TMS had little effect on the bimanual antiphase task. The equal effect of right and left hemisphere stimulation indicates that neither motor cortex is dominant for simple bimanual in-phase movement. The smaller influence of contralateral stimulation and the greater effect of ipsilateral stimulation during bimanual in-phase movement compared with unimanual movement suggest hemispheric coupling. The antiphase movements were resistant to TMS disruption, and this suggests that control of rhythm differs in the 2 tasks. TMS produced a transient asynchrony of movements on the 2 sides, indicating that both motor cortices might be downstream of the clocking command or that the clocking is a consequence of the 2 hemispheres communicating equally with each other.     

Unimanual and bimanual voluntary movement in Huntington's disease

Unimanual and bimanual cyclical forearm movements were studied in 15 Huntington's disease (HD) patients and 15 healthy, gender- and age-matched controls. Whereas the unimanual task was only performed at maximal speed, the bimanual movements were performed according to the in-phase and anti-phase mode at different cycling frequencies. The HD patients also performed the tasks after 12 months of follow-up. Findings revealed that maximal cycling frequency during unimanual movement was significantly lower in HD patients as compared with controls. In addition, measures of relative phasing established that bimanual cyclical movements were performed with lower accuracy and higher variability in HD patients. The differential variability between both groups was magnified by increasing the cycling frequency and coordinative complexity whereas only coordinative complexity differentially affected the accuracy of relative phasing. The obtained performance measures were found to be significantly correlated with disease duration (unimanual) and with the score on the total motor scale, the Mini-Mental State Examination and the Stroop Interference Test (uni- and bimanual). After 12 months, maximal cycling frequency of unimanual elbow flexion–extension was significantly decreased in HD patients whereas the quality of the in-phase and anti-phase movement patterns remained stable. Electronic Publication     

The positive effect of mirror visual feedback on arm control in children with Spastic Hemiparetic Cerebral Palsy is dependent on which arm is viewed

Mirror visual feedback has previously been found to reduce disproportionate interlimb variability and neuromuscular activity in the arm muscles in children with Spastic Hemiparetic Cerebral Palsy (SHCP). The aim of the current study was to determine whether these positive effects are generated by the mirror per se (i.e. the illusory perception of two symmetrically moving limbs, irrespective of which arm generates the mirror visual feedback) or by the visual illusion that the impaired arm has been substituted and appears to move with less jerk and in synchrony with the less-impaired arm (i.e. by mirror visual feedback of the less-impaired arm only). Therefore, we compared the effect of mirror visual feedback from the impaired and the less-impaired upper limb on the bimanual coupling and neuromuscular activity during a bimanual coordination task. Children with SHCP were asked to perform a bimanual symmetrical circular movement in three different visual feedback conditions (i.e. viewing the two arms, viewing only one arm, and viewing one arm and its mirror image), combined with two head orientation conditions (i.e. looking from the impaired and looking from the less-impaired body side). It was found that mirror visual feedback resulted in a reduction in the eccentric activity of the Biceps Brachii Brevis in the impaired limb compared to the condition with actual visual feedback from the two arms. More specifically, this effect was exclusive to mirror visual feedback from the less-impaired arm and absent when mirror visual feedback from the impaired arm was provided. Across conditions, the less-impaired arm was the leading limb, and the nature of this coupling was independent from visual condition or head orientation. Also, mirror visual feedback did not affect the intensity of the mean neuromuscular activity or the muscle activity of the Triceps Brachii Longus. It was concluded that the positive effects of mirror visual feedback in children with SHCP are not just the result of the perception of two symmetrically moving limbs. Instead, in order to induce a decrease in eccentric neuromuscular activity in the impaired limb, mirror visual feedback from the ‘unaffected’ less-impaired limb is required.     

Visual feedback alters the variations in corticospinal excitability that arise from rhythmic movements of the opposite limb

Augmented visual feedback can have a profound bearing on the stability of bimanual coordination. Indeed, this has been used to render tractable the study of patterns of coordination that cannot otherwise be produced in a stable fashion. In previous investigations (Carson et al. 1999), we have shown that rhythmic movements, brought about by the contraction of muscles on one side of the body, lead to phase-locked changes in the excitability of homologous motor pathways of the opposite limb. The present study was conducted to assess whether these changes are influenced by the presence of visual feedback of the moving limb. Eight participants performed rhythmic flexion–extension movements of the left wrist to the beat of a metronome (1.5 Hz). In 50% of trials, visual feedback of wrist displacement was provided in relation to a target amplitude, defined by the mean movement amplitude generated during the immediately preceding no feedback trial. Motor potentials (MEPs) were evoked in the quiescent muscles of the right limb by magnetic stimulation of the left motor cortex. Consistent with our previous observations, MEP amplitudes were modulated during the movement cycle of the opposite limb. The extent of this modulation was, however, smaller in the presence of visual feedback of the moving limb (FCR ²=0.41; ECR ²=0.29) than in trials in which there was no visual feedback (FCR ²=0.51; ECR ²=0.48). In addition, the relationship between the level of FCR activation and the excitability of the homologous corticospinal pathway of the opposite limb was sensitive to the vision condition; the degree of correlation between the two variables was larger when there was no visual feedback of the moving limb. The results of the present study support the view that increases in the stability of bimanual coordination brought about by augmented feedback may be mediated by changes in the crossed modulation of excitability in homologous motor pathways.     

Cerebral midline structures in bimanual coordination

In six healthy right-handed volunteers, we compared the cerebral activation pattern related to unimanual right- and left-hand movements and to bimanual in-phase and anti-phase movements using functional magnetic resonance imaging (fMRI). Internally paced unimanual finger-to-thumb opposition movements led to a strong contralateral activation of primary sensorimotor areas in all six subjects. Midline activity was lateralized to the left side during right-hand movements, but to both sides during left-hand movements. Activity patterns of bimanual in-phase movements resembled the combined activity patterns of the two unimanual conditions: right and left hemispheric activations of the primary sensorimotor cortices and predominantly left-sided medial frontal activity. In contrast, during anti-phase movements, we observed a clear increase in activity, in both right and left frontal midline areas and in right hemispheric, mainly dorsolateral premotor areas compared to in-phase movements. These results indicate that frontal midline activity is not specific for bimanual movements per se. It can already be involved during simple unimanual movements but becomes progressively more involved during more complex aspects of movement control. Received: 20 September 1998 / Accepted: 24 February 1999     

Coordinative and limb-specific control of bimanual movements in patients with Parkinson's disease and cerebellar degeneration

The present study examined the effects of basal ganglia and cerebellar pathology on bimanual coordination using patients with Parkinson's disease (PD) and cerebellar dysfunction (CD). Twenty patients with idiopathic PD (10 untreated early and 10 advanced PD), 10 patients with cerebellar degeneration, and 11 normal subjects were instructed to perform in-phase and anti-phase bimanual coordination movements. The results indicated that while the quality of coordinated bimanual movements in untreated early PD and CD patients was not significantly different from that of normal controls, advanced PD patients exhibited reduced synchronized coordination during the faster anti-phase mode. This suggests that the observed bimanual coordination abnormalities in PD are not an early sign of the pathophysiology of the disease, and cerebellar degeneration may have minimal consequences on synchronized coordination between the limbs. In terms of the parameterization of individual limb movements, CD patients showed a tendency for hypermetric impairments with more irregular movements, while PD patients exhibited relatively slower limb movements and lower amplitudes than normal controls. Overall, the current data provide evidence of the specific functions of different neural structures involved in the pathological process of PD and CD on bimanual coordination.     

Bimanual 1:1 with 90° continuous relative phase: difficult or easy!

The purpose of the present experiment was to observe the performance of participants attempting to produce a 1:1 bimanual coordination pattern with 90° relative phase between the arms when feedback concerning the movement of the two limbs was integrated within a Lissajous plot and when this information was withdrawn. One group was paced with an auditory metronome and the other was encouraged to increase frequency when they fell below the goal frequency. We predicted that providing a salient integrated feedback display without a metronome would allow participants to effectively tune-in the goal relative phase pattern within several minutes; instead of several days as typically found in the literature when the metronome was used. The data indicated remarkably effective performances after 5 min of practice when the metronome was not used, with motion of both limbs harmonic in nature, and continuous relative phase errors (~10°) and standard deviation of continuous relative phase (~10°) relatively small. This seems remarkable given that this coordination pattern has proven relatively difficult to perform under normal and Lissajous feedback conditions even after several days of practice. As predicted relative phase errors and variability increased substantially when the metronome was used. When the extrinsic feedback was withdrawn all participants tended to drift from the required 90° relative phase, but the cycle duration variability in the two limbs remained stable and limb motion remained harmonic in nature. The current findings suggest that some of the difficulty typically associated with producing various relative phase patterns is due to the less than optimal perceptual information available in the various testing situations and the use of pacing metronomes.