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The control of spatially constrained unilateral and bilateral movements : hemispheric and callosal contributions Garry, Michael Ian

Abstract

When a person performs an arm movement that requires concurrent activity of the contralateral arm, it is common to observe a decrement in performance relative to when the same task is performed in isolation (Ohtsuki, 1994). Thus, if a task requires a rapid movement of one arm, that movement will, in general, be executed more quickly compared with a condition where the opposite arm is moved simultaneously (Fowler et al., 1991; Marteniuk & MacKenzie, 1980). Reaction time is similarly affected when simultaneous bilateral actions are performed, with bilateral movements requiring more time for movement initiation (Anson & Bird, 1993; Ohtsuki, 1994). Recently it has been suggested that the increase in reaction time accompanying bilateral movements might reflect an inhibitory interaction between the motor cortexes of the left and right hemispheres through the corpus callosum, resulting in an increase in the time required for muscle activation (Ohtsuki, 1994). Recent studies have provided support for this interpretation (Meyer & Voss, 2000; Taniguchi et al., 2001). Despite empirical support, however, a number of studies have yielded results inconsistent with this proposal in that bilateral movements did not lead to increases in reaction time (Anson & Bird, 1993; Swinnen et al., 1995). We (Garry & Franks, 2000) also reported a failure for reaction time to increase with bilateral movements, but only when the task demanded spatial precision of the right arm. When left arm precision was required, reaction time increases were observed. Because our task involved proximal muscles, which can be controlled through ipsilateral pathways (Berlucchi et al., 1994; Brinkman & Kuypers, 1973), we interpreted this result as evidence that under certain conditions (right arm precision), bilateral movements can be initiated via a single hemisphere eliminating the inhibitory interhemispheric interactions that accompany bilateral movements. Although experiments 1 and 2 were consistent with the predictions of this model, experiment 3 failed to provide support. An alternative model involving premotor cortex mechanisms was proposed.

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