2014 年 3 巻 3 号 p. 297-306
In primates, unilateral voluntary movements are preferentially controlled by the primary motor cortex (M1) contralateral to the side performing the movement. However, it has been reported that the M1 ipsilateral to the side performing the movement (ipsi-M1) is also activated during unilateral voluntary movements. Recently, studies involving transcranial magnetic stimulation (TMS) or functional magnetic resonance imaging (fMRI) techniques have gradually elucidated the neural mechanisms responsible for modulating ipsi-M1 activity. In particular, the modulation of ipsi-M1 activity is likely to occur in a task-dependent manner, and is also closely associated with advancing age. In addition, ipsi-M1 excitability is suppressed during the acquisition phase of motor learning. Previous studies have suggested that the modulation of ipsi-M1 activity occurs via changes in the activation of the corpus callosum pathways linking the bilateral M1. In this article, we will broadly review the features of ipsi-M1 activity, observed during the execution of unilateral movements, as well as the detailed neural mechanisms underlying the modulation of ipsi-M1 activity. Understanding the role played by ipsi-M1 activity during voluntary movements would improve our knowledge of human motor control systems.