The bilateral origin of movement-related potentials preceding unilateral actions

It is as yet unclear why a unilateral self-paced movement in human and nonhuman primates is preceded by a bilateral Bereitschaftspotential (BP) or readiness potential (RP). The RP consists of an early symmetrical part (termed BP1 or RP), presumably of supplementary motor area (SMA) origin, and a later contralaterally dominant part (termed BP2 or NS'), to which the primary motor cortex (M1) is thought to contribute. Apart from the SMA there are other motor areas in the mesial cortex, which might provide additional sources for these slow waves. Although bilateral intracortical sources of the RP are found in the premotor cortex (Sasaki & Gemba, 1991), they play nearly any role in most discussions on the RP. Recently the very existence of the ipsilateral RP over MI has been doubted. RP recordings of two patients with an intracerebral electrode in the ventro-intermedius nucleus (Vim) of the thalamus are shown, suggesting that the ipsilateral RP is not the consequence of volume conduction or signal transmission via the corpus callosum. Rather they point to a subcortical source, from where the ipsilateral cortex is activated. Anatomical and recent RP recordings from Vim and subthalamic nucleus seem to support this interpretation