Role of lateral non-primary motor cortex in humans as revealed by epicortical recording of Bereitschaftspotentials

In order to clarify the role of the lateral non-primary motor area in the control of voluntary movements, we studied movement-related cortical potentials (MRCPs) by direct epicortical recording from the lateral frontal lobe in nine patients with intractable partial epilepsy as a part of presurgical evaluation. We adopted movement tasks involving different body sites: eye closing, lip pursing, shoulder abduction, middle finger extension, thumb abduction, and foot dorsiflexion. We found that one or two small areas on the caudal lateral convexity of the frontal lobe generated pre-movement potential shifts regardless of the sites of movement (omni-Bereitschaftspotential; "omni-BP"). Such regions were located at or just rostral to the primary motor face area in six subjects, and at or rostral to the primary motor upper extremity area in three. Moreover, half of those areas were identified just adjacent (either rostral or caudal) to the primary negative motor area (PNMA), a cortical area of the lateral frontal lobe where negative motor responses were elicited by electric cortical stimulation. In conclusion, it is suggested that the lateral non-primary motor area plays a significant role, and has a close and direct relationship with other cortical areas in the frontal lobe, just like its counterpart on the mesial frontal cortex (supplementary negative motor area, SNMA).