Field potential change in the prefrontal cortex of the left hemisphere during learning processes of reaction time hand movement with complex tone in the monkey.

Field potentials were recorded with electrodes implanted in various cortical areas while a naive monkey was learning reaction time hand movements with complex tone. When cortical surface-negative, depth-positive potential (at a latency of about 80 ms after a stimulus onset) appeared in the rostral bank of the inferior limb of the arcuate sulcus of the left cerebral hemisphere, and became gradually larger, the monkey began to respond to the stimulus with the movement. As the potential in the prefrontal (prearcuate) cortex and the cerebellar-mediated potential in the motor cortex gradually increased with further training, the movement became quicker and more skillful. Three naive monkeys achieved the movement with complex tone in shorter training days than the movement with pure tone; the movement with pure tone was not accompanied by any significant potential in the prefrontal cortex. It is deduced from the present study, and previous studies on visuo-initiated movements, that the prefrontal area, especially in the left hemisphere, plays a significant role for a monkey to associate a stimulus with appropriate motor execution.