Previous research applying transcranial magnetic stimulation during unimanual reaction time tasks indicates a transient change in the inhibitory influence of the dorsal premotor cortex over the contralateral primary motor cortex shortly after the presentation of an imperative stimulus. The degree of interhemispheric inhibition from the dorsal premotor cortex to the contralateral primary motor cortex shifts depending on whether the targeted effector representation in the primary motor cortex is selected for movement. Further, the timing of changes in inhibition covaries with the selection demands of the reaction time task. Less is known about modulation of dorsal premotor to primary motor cortex interhemispheric inhibition during the preparation of bimanual movements. In this study, we used a dual coil transcranial magnetic stimulation to measure dorsal premotor to primary motor cortex interhemispheric inhibition between both hemispheres during unimanual and bimanual simple reaction time trials. Interhemispheric inhibition was measured early and late in the ‘pre-movement period’ (defined as the period immediately after the onset of the imperative stimulus and before the beginning of voluntary muscle activity). We discovered that interhemispheric inhibition was more facilitatory early in the pre-movement period compared with late in the pre-movement period during unimanual reaction time trials. In contrast, interhemispheric inhibition was unchanged throughout the pre-movement period during symmetrical bimanual reaction time trials. These results suggest that there is greater interaction between the dorsal premotor cortex and contralateral primary motor cortex during the preparation of unimanual actions compared to bimanual actions.

中文翻译：

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背侧前运动皮层和初级运动皮层之间的半球间抑制在单手运动准备期间释放，但双手运动不释放

先前在单手反应时间任务中应用经颅磁刺激的研究表明，在出现命令性刺激后不久，背侧前运动皮层对对侧初级运动皮层的抑制影响会发生短暂变化。从背侧前运动皮层到对侧初级运动皮层的半球间抑制程度会发生变化，具体取决于初级运动皮层中的目标效应器表示是否被选择进行运动。此外，抑制变化的时间随反应时间任务的选择要求而变化。关于双手运动准备过程中背侧前运动对初级运动皮层半球间抑制的调节知之甚少。在这项研究中，我们使用双线圈经颅磁刺激来测量单手和双手简单反应时间试验中两个半球之间的背侧前运动到初级运动皮层的半球间抑制。在“运动前阶段”（定义为命令性刺激开始后和随意肌肉活动开始前的时期）的早期和晚期测量半球间抑制。我们发现，在单手反应时间试验中，与运动前后期相比，运动前早期的半球间抑制更为容易。相比之下，在对称双手反应时间试验中，半球间抑制在整个运动前阶段没有变化。这些结果表明，与双手动作相比，在准备单手动作期间，背侧前运动皮层和对侧初级运动皮层之间存在更大的相互作用。