Asymmetries in unimanual and bimanual coordination: evidence from behavioural and transcranial magnetic stimulation studies

Deborah Faulkner

Research output: ThesisDoctoral Thesis

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The issue of the laterality of control during unimanual and bimanual coordination was addressed in this thesis. Two tasks were used throughout: a repetitive discrete response task (finger tapping) and a continuous task (circle-drawing). Different mechanisms have been implicated in the temporal control of repetitive discrete movements and continuous movements. The tasks also differ in the degree of spatiotemporal coordination required which might have important implications in the question of laterality of control. The first section of the thesis examined between-hand differences in the dynamics of performance during unimanual and bimanual coordination. During tapping, the dominant hand was faster and less temporally variable than the nondominant hand. During circle drawing the dominant hand was faster, more accurate, less temporally and spatially variable, and produced smoother trajectories than the nondominant hand. During bimanual coordination, several of these asymmetries were attenuated: the rate of movement of the two hands became equivalent (the hands became temporally coupled), the asymmetry in temporal variability during tapping was reduced, and the asymmetry in trajectory smoothness during circle drawing was reduced. The second section of the thesis examined the effects of disrupting motor processes with transcranial magnetic stimulation (TMS) over the left or right primary motor cortex (M1) on the ongoing performance of the hands. In the first study, TMS over left or right M1 during unimanual tapping caused large disruptions to tapping with the contralateral hand but had little effect on the ipsilateral hand. In contrast, for a subset of trials during bimanual tapping, two lateralized effects of stimulation were seen: the effect of TMS on the contralateral hand was greater after stimulation over left M1 than after stimulation over right M1, and prolonged changes in inter-tap interval were observed in the left hand regardless of the side of stimulation. In the second study, TMS over left M1 during circle drawing decreased the accuracy of drawing with both the contralateral and ipsilateral hand, whereas TMS over right M1 decreased accuracy of drawing only with the contralateral hand. This lateralized effect was not limited to the bimanual case, but was also apparent during unimanual drawing. The final chapter addressed issues in bimanual motor control after unilateral stroke. Performance of the affected limb was examined during unimanual and bimanual coordination in a group of stroke patients with varying levels of impairment. The results indicated an improvement in the performance of the affected limb for some patients with mild to moderate, but not severe upper limb motor deficits during bimanual movement. The improvements were limited to the patients who showed evidence of temporal coupling between the hands. These findings support the hypothesis that the dominant motor cortex has a role in the control of both hands during bimanual coordination. In addition, the dominant hemisphere appears to play a role in controlling both hands during unimanual movements which require a greater degree of spatiotemporal coordination. The final study suggests that temporal coupling between the limbs is crucial for the facilitation of performance of the affected limb during bimanual coordination, which has both theoretical and practical implications.
Original languageEnglish
QualificationDoctor of Philosophy
Publication statusUnpublished - 2009


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