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Coordination between arm and leg movements during locomotion.

To evaluate the contrasting dynamical and biomechanical interpretations of the 2:1 frequency coordination between arm and leg movements that occurs at low walking velocities and the 1:1 frequency coordination that occurs at higher walking velocities, the authors conducted an experiment in which they quantified the effect of walking velocity on the stability of the frequency and phase coordination between the individual limb movements. Spectral analyses revealed the presence of 2:1 frequency coordination as a constant feature of the data in only 3 out of 8 participants at walking velocities ranging from 1.0 to 2.0 km/h, in spite of the fact that the eigenfrequencies of the arms were rather similar across participants. The degree of interlimb coupling, as indexed by weighted coherence and variability of relative phase, was lower for the arm movements and for ipsilateral and diagonal combinations of arm and leg movements than for the leg movements. Furthermore, the coupling between all pairs of limb movements was found to increase with walking velocity, whereas no clear signs were observed that the switches from 2:1 to 1:1 frequency coordination and vice versa were preceded by loss of stability. Therefore, neither a purely biomechanical nor a purely dynamical model is optimally suited to explain these results. Instead, an integrative model involving elements of both approaches seems to be required.

Adult↗

The development of locomotor coordination: longitudinal change and invariance.

Developmental sequence, relative timing, center of gravity, and phase-plane analyses were used to study a minimum of 15 years of longitudinal, filmed data on the development of hopping in 7 children. The developmental sequences revealed common, qualitative changes in the movement of the children, although each child progressed through the changes at his/her own rate. The timing analyses showed that, in the advanced hop, the tightest limb relationships were found within the hopping leg, then between contralateral limbs of the same girdle, and then between legs and arms. Relative-timing calculations revealed (a) intralimb, timing invariances that were present in first attempts to perform the skill at age 3 and remained for 15 years across all developmental levels; (b) emergent, interlimb timings that gradually became invariant; and (c) intra- and interlimb timing showing gradual development over the 15 years. One invariant, the time between landing and deepest knee flexion, is also invariant in the walk and the run (Shapiro, Zernicke, Gregor, & Diestel, 1981). Phase plane analyses indicated that the timing of peak and zero velocities may be the coordinative constant accounting for a relative timing invariance between the two legs. Position of the body's center of gravity may explain the invariant relative time between landing and deepest knee flexion, or the explanation could lie in the "equation of constraint" regulating joint equilibrium points. The data suggest that modeling the developing hop as the evolving interaction of four vibratory systems would be promising.

Journal Article↗

Acquiring bimanual skills: contrasting forms of information feedback for interlimb decoupling.

The present experiments addressed the learner's capability to perform different upper-limb actions simultaneously with the help of various sources of information feedback. An elbow flexion movement was made in the left limb together with a flexion-extension-flexion movement in the right limb. Interlimb interactions were assessed at the structural as well as the metrical level of movement specification during acquisition and retention. Despite a strong initial tendency for the limbs to be synchronized, findings revealed that Ss became gradually more successful in interlimb decoupling as a result of practice with augmented feedback. However, detailed knowledge of movement kinematics was no more effective than global outcome information for interlimb decoupling, indicating that knowledge of results may have more potential for acquiring multiple degree-of-freedom tasks than previously believed. Finally, the data support the general notion that learning new coordination tasks involves the suppression of preexisting preferred coordination tendencies, which is often a prerequisite for building new coordination modes.

Adolescent↗

Human interlimb reflexes evoked by electrical stimulation of cutaneous nerves innervating the hand and foot.

There is some discrepancy over the extent to which reflex pathways from different cutaneous nerves in the hand and foot link the cervical and lumbar spinal cord in neurologically intact humans. The present experiments were designed to determine whether stimulation of a cutaneous nerve in the foot or in the hand evoked reflexes in the non-stimulated limbs (interlimb reflexes). Reflexes were elicited by stimulating (5x1-ms pulses at 300 Hz) the superficial peroneal (SP; innervates the foot dorsum) or superficial radial (SR; innervates the dorsolateral portion of the hand) nerve while subjects (n=10) performed focused contractions of different upper and lower limb muscles. Reflex responses were divided into early (<75 ms), middle (75-120 ms), and late (>120 ms) epochs as determined from averages of 50 sweeps of stimulus-locked electromyographic activity. Significant interlimb reflexes were found at the early latency in 44/106 and 44/103 muscles sampled after SP and SR nerve stimulation, respectively. At the middle latency, significant interlimb reflexes were seen in 89/106 and 87/103 muscles sampled after SP and SR nerve stimulation, respectively. Interlimb reflexes were seen when stimulating at the wrist (i.e. SR nerve) and when stimulating at the ankle (i.e. SP nerve) with an equal probability. The results show that interlimb cutaneous reflexes are widely distributed in humans. The mean latency of the earliest response was quite short and may be mediated by a propriospinal pathway. Functionally, these pathways may provide a substrate for transferring information to coordinate movements between the limb segments.

Action Potentials↗

Repetitive transcranial magnetic stimulation of the supplementary motor area (SMA) degrades bimanual movement control in humans.

Moving the upper limbs at a common tempo according to an in-phase or anti-phase mode represents elementary coordination dynamics. Previously, the role of the supplementary motor area (SMA) has been emphasized for successful production of these patterns. The objective of this study was to investigate whether repetitive transcranial magnetic stimulation (rTMS) of the SMA at 5 Hz can interfere with these isofrequency configurations in the post-stimulation stage. Results showed a deterioration of temporal control as a function of coordinative complexity. This effect was associated with a decrease in the functional coupling between the primary motor cortices, as measured by electroencephalographic coherence. These data suggest that rTMS of the SMA can modify interhemispheric communication and accordingly modulate interlimb behavior.

Adult↗

Dynamical aspects of learning an interlimb rhythmic movement pattern.

Learning a bimanual rhythmic task is explored from the perspective that motor skill acquisition involves the successive reparameterization of a dynamical control structure in the direction of increasing stability, where the intentional process of reparameterization is itself dynamical. Subjects learned to oscillate pendulums held in the right and left hands such that the right hand frequency was twice that of the left (2:1 frequency lock). Over 12 learning sessions of 20 trials each, we interpreted the decreasing fluctuations in the frequency locking to be an index of the increasing concavity of the underlying potential, a measure of stability; the time required to achieve the 2: 1 pattern was interpreted as indexing the relaxation time of an intentional dynamic. Power spectral analyses of the phase velocity ratio exhibited two strategies for acquiring the interlimb movement pattern: (a) adding spectral peaks at integer multiples of the left hand frequency or (b) distributing power across many frequencies in a l/f-like manner. Results are discussed in terms of the promise of a dynamical approach to learning coordinated movements.

Journal Article↗

Differences in control of limb dynamics during dominant and nondominant arm reaching.

This study compares the coordination patterns employed for the left and right arms during rapid targeted reaching movements. Six right-handed subjects reached to each of three targets, designed to elicit progressively greater amplitude interaction torques at the elbow joint. All targets required the same elbow excursion (20 degrees ), but different shoulder excursions (5, 10, and 15 degrees, respectively). Movements were restricted to the shoulder and elbow and supported on a horizontal plane by a frictionless air-jet system. Subjects received visual feedback only of the final hand position with respect to the start and target locations. For motivation, points were awarded based on final position accuracy for movements completed within an interval of 400-600 ms. For all subjects, the right and left hands showed a similar time course of improvement in final position accuracy over repeated trials. After task adaptation, final position accuracy was similar for both hands; however, the hand trajectories and joint coordination patterns during the movements were systematically different. Right hand paths showed medial to lateral curvatures that were consistent in magnitude for all target directions, whereas the left hand paths had lateral to medial curvatures that increased in magnitude across the three target directions. Inverse dynamic analysis revealed substantial differences in the coordination of muscle and intersegmental torques for the left and right arms. Although left elbow muscle torque contributed largely to elbow acceleration, right arm coordination was characterized by a proximal control strategy, in which movement of both joints was primarily driven by the effects of shoulder muscles. In addition, right hand path direction changes were independent of elbow interaction torque impulse, indicating skillful coordination of muscle actions with intersegmental dynamics. In contrast, left hand path direction changes varied directly with elbow interaction torque impulse. These findings strongly suggest that distinct neural control mechanisms are employed for dominant and non dominant arm movements. However, whether interlimb differences in neural strategies are a consequence of asymmetric use of the two arms, or vice versa, is not yet understood. The implications for neural organization of voluntary movement control are discussed.

Adult↗

Varieties of paw and digit movement during spontaneous food handling in rats: postures, bimanual coordination, preferences, and the effect of forelimb cortex lesions.

This study describes how rats use their paws and digits when handling a wide range of foodstuffs, including food pellets, grapes, sunflower seeds, shelled and unshelled peanuts, and different sized pastas, etc. Analysis of videorecordings show that the rats display digit postures that include variations in the spacing of the digits, differences in the relative use of different digits, and interlimb differences in paw and digit posture. The rats also display limb preferences in that one paw is used in a supporting function while the other rotates, flips, or pushes the food as is required by the shape of the item. There is a significant correlation between the paw used for manipulation and food items of similar shape but no correlation between the limb used for manipulation and that used for skilled reaching. Small unilateral lesions to the forepaw area of somatic sensorimotor cortex produced impairments in use of the paw contralateral to the lesions. These results: (1) reveal a surprising complexity in the way in which rats use their paws and digits in manipulating food; (2) show that rats have limb preferences in spontaneous food handling; and (3) show that manipulatory dexterity is dependent upon the integrity of the forelimb area of motor cortex. The results are discussed in relation to the evolution of motor skill, the use of rats for investigating questions of motor system organization, neural plasticity, and recovery of function after brain damage.

Animals↗

Time structure of a goal-directed bimanual skill and its dependence on task constraints.

The aim of the study was to elucidate the underlying principles of bimanual coordination and to establish quantitative coordination criteria. Healthy human subjects were instructed to open a loaded drawer with the left hand and to grasp, lift and reinsert with the right hand a small peg in the drawer recess. This bimanual goal-oriented task was executed promptly and consistently after a few trials. The temporal structure of the individual limb actions was assessed for computing interlimb synchronization and temporal correlation. In all subjects, both hands were well synchronized at the goal with high intermanual correlation in reaching the goal (event times of drawer opening and grasping the peg). This temporal goal-invariance was independent of movement speed and of the highly variable timing of the individual hands and persisted when subjects were blindfolded. Unilateral loading of the pulling hand and cutaneous anesthesia of the left index finger and thumb used for grasping the drawer handle significantly increased the pull-phase. This slowing of the left hand was matched by an adaptive delay of the right non-disturbed hand, thus preserving goal invariance. As a working hypothesis, we propose that multimodal sensory signals generated in the leading arm be transmitted centrally to re-parameterize the non-disturbed arm.

Adult↗

Inter- and intralimb transfer of a bimanual task: generalisability of limb dissociation.

The present study examined whether the ability to dissociate bimanual limb movements following learning of a new coordination task (i.e. star-line drawing paradigm) can be generalised to different effector systems, as expressed by inter- and intralimb transfer. In Experiment 1, subjects practised the 'Line-Star' task (i.e. left arm traced the line/right arm traced the star) and then transferred this pattern to its symmetry partner: the 'Star-Line' task (left arm star/right arm line). In Experiment 2, intralimb transfer from the shoulder-elbow (proximal) to the wrist-finger joints (distal), and vice versa, was investigated. Results revealed positive interlimb transfer among symmetry partners of the star-line movement. Moreover, learning the star-line task spontaneously transferred from the trained to the untrained effector system whereby proximal to distal transfer was larger than vice versa. It is concluded that learning to spatially dissociate the movements of both limbs is generalisable to different motor conditions even though transfer to some conditions is suboptimal. It is hypothesised that the nature of the representation of the spatial interference task is largely effector independent.

Adult↗

Effects of movement frequency and joint kinetics on the joint coordination underlying bimanual circle drawing.

Ten healthy participants performed bimanual symmetric and asymmetric circle drawing at 4 frequencies. The authors partitioned the variance of the joint configuration across repetitions into 1 component representing equivalent joint configurations with respect to achieving stability of the mean hand path (i.e., goal-equivalent variance, GEV) and 1 component leading to a variable hand path (non-goal-equivalent variance, NGEV) across cycles. Higher frequencies led to increased NGEV related to control of the nondominant hand and to the relative position and orientation between the hands during asymmetric drawing. The results were related to differences in muscle and interaction moments between the arms, and they suggest a possible relationship between the ability to use intersegmental forces and the stability of interlimb synergy.

Adult↗

Temporal control of a bimanual task in patients with cerebellar dysfunction.

The objective of the study was to investigate whether temporal control during a goal-directed bimanual action is disturbed in cerebellar patients. The task was to open a drawer with one hand and to reach and grasp a small object with the other hand. Interlimb coupling was determined at start and end positions. Cerebellar patients as compared to normal subjects showed an increased offset for initiating the hand movements which denotes the involvement of the cerebellum for organizing the components underlying the bimanual task. The reduced simultaneity was caused by a delayed movement onset of the grasping (non-leading) hand as compared to the pulling hand. Lack of vision increased the degree of desynchronization for the patients at the start position, indicating that they depended on external cues for organizing the temporal coordinates of the combined motion pattern. At the goal, the magnitude of temporal offset was similar/smaller than at movement onset which can be related to feedforward mechanisms that are used to anticipate the limbs' end positions. These results confirm the role of the cerebellum for planning the temporal ordering of movement sequences into a synergic action.

Adult↗

Spontaneous and intentional pattern switching in a multisegmental bimanual coordination task.

Two experiments required right-handed subjects to trace circular trajectories while complying with either a symmetric or asymmetric pattern. In symmetric patterns, circles were traced in a mirror image either inward or outward. In asymmetric patterns, circles were traced in the same direction either clockwise or counterclockwise. Subjects were instructed to trace with spatial accuracy while maintaining a strict temporal relationship to a metronome that scaled movement rates from 1.25 to 3 Hz. The symmetric patterns were more stable than asymmetric patterns; the circularity of trajectories was greater for the dominant side; and there were spontaneous reversals in the direction of circling in the nondominant limb when performing asymmetric patterns. The second experiment examined the same subjects under the instruction of intentionally changing the pattern by reversing the left or right limb circling direction when cued to do so. The degree of interlimb interference was highly asymmetric and contingent on the direction of pattern change. Intentional direction reversals were more expedient and with less disruption to the contralateral limb when asymmetric to symmetric pattern changes were effected through a reversal in the direction of nondominant side. The results are interpreted with reference to evidence that the supplementary motor area mediates descending input to the upper limbs during disparate bimanual actions, but not during symmetric actions.

Adult↗

Dissociation of grip/load-force coupling during a bimanual manipulative assignment.

The aim of the present study was to examine interlimb interactions of grasping forces during a bimanual manipulative assignment that required the execution of a drawer-opening task with the left hand and an object-holding task with the right hand. Compared with the unimanual performance, the grip/load-force ratio of the object-holding task was shifted towards that of the simultaneously executed drawer-opening task. This shows that force parameterization of the dynamic activity interacted with that of the static activity. That the increased force ratio only involved modification of grip force, while load force was held constant, indicates a disruption of the commonly observed co-variation of both forces during a manipulative action. These data are consistent with the notion that the coordinative constraint between grip and load force is a flexible parameter.

Adult↗

Coordination of coupled hand and foot movements during childhood.

To acquire further insight into the neural mechanisms governing the association of voluntary oscillations of ipsilateral hand and foot we investigated when and how coordination of such coupling develops in children 7-10 years old. Sixty-six children were asked to rhythmically oscillate their right hand and foot, paired in-phase or anti-phase (i.e. rotating in the same or in the opposite angular direction). Angular displacement was monitored by a potentiometric technique, and EMGs from extensor carpi radialis (ECR) and tibialis anterior (TA) were recorded. All subjects were able to couple in-phase oscillations, but 13 of them failed to perform the anti-phase task. Maximal frequency of oscillation was found to be positively correlated with age. Phase-relations between hand and foot oscillations and between onsets of the EMG activity in hand and foot movers were measured in 37 of the children. During in-phase coupling limb oscillations were kept in an almost perfect synchrony by three different modalities of muscle recruitment. Ten of the youngest children activated TA before ECR, while 13 of the oldest subjects activated ECR before TA, as do adults. The remaining 14 children (7-8 years old) activated the two muscles almost synchronously. During anti-phase coupling, most of the younger children (20) showed a strict phase-opposition between both EMG onsets and movements. The remaining 10 (9-10 years old) activated the ECR first. The hand frequency-response (i.e. the phase-relation between the onset of the EMG and the related movement) showed age-related changes, corresponding to the behaviour of a mass-spring model (with lumped parameters) decreasing its resonant frequency. Instead, the foot frequency-response remained unchanged. The age-related modifications of the hand frequency-response adequately explain the changes of the interlimb relations described above. These results show that central structures controlling hand and foot coupling are still immature before 10 years of age and reinforce the view that in-phase and anti-phase coupling require separate neural controls.

Adult↗