Functional properties of the primary motor cortex and ventral premotor cortex in the monkey during a visually guided jaw-movement task with a delay period

This study investigated single neuronal activity in the face area of the pr imary motor cortex (MI) and ventral part of the premotor cortex (PMv) while a monkey performed a visually guided jaw-movement task with a delay period . When the monkey executed the jaw movements, 48 MI and 53 PMv neurons show ed statistically significant activities time-locked to jaw movements and we re defined as movement-related neurons. The activities of movement-related neurons could be classified into phasic, phasic-tonic and tonic patterns ba sed on the changes in discharge rate. Most of the neurons exhibiting phasic and phasic-tonic activities probably contributed to the initiation of jaw movements, since they exhibited transient responses immediately after the o nset of the go-cue indicating the jaw movement. In contrast, the sustained activity of the movement-related neurons exhibiting phasic-tonic and tonic activities may be involved in controlling and/or maintaining jaw position. Sustained activity was also detected during the delay period in 4 MI and 29 PMv neurons and these neurons were defined as set-related neurons. It is t hought that these set-related neurons are involved in the preparation for t he subsequent jaw movement, since the masticatory muscles showed no signifi cant changes during the delay period. These findings suggest that the MI ma y be involved predominantly in the initiation and control of jaw movements, and that the PMv may be involved in motor preparation, and may play a role as a higher-order motor area related to the initiation and control of jaw movements. (C) 2000 Elsevier Science B.V. All rights reserved.