Neurons in Dorsal Premotor Cortex Adapted to Abrupt External Perturbation in Reaching Behavior

When confronted with an abrupt external perturbation force during movement, a subject will continuously adjust its behavior to adapt to the instant change. Although such adaptation is important for the subject, few studies have attempted to elucidate the associated potential neuronal mechanisms. This work aims to reveal the neural control system compensation for various types of external disturbance. We applied external perturbation to monkeys while they performed a reaching task, and chronically (long-term) recorded the neuronal activity in the dorsal premotor (PMd) cortex. The results show that PMd neurons did not respond to the “go” signal under the normal task condition without perturbation. In contrast, in the adaptation phase, a subpopulation of neurons developed time-locked activity to the “go” signal, which is a conditioned stimulus associated with the impending perturbation. In the three-week experiment on one monkey for eight targets, the neuronal activity increased as adaptation was processed, remained at a constant level for a couple of days during the extinction phase, and then gradually faded. In the single-day experiment on another monkey for one target, the neuronal activity increased as adaptation was processed, remained at a constant level for a couple of sessions, and gradually faded over a couple of sessions. We postulate that the increases in activity during adaptation to the external perturbation might reflect a preparation for the impending response.