Functional role of corticoperipheral loop circuits during voluntary movements in the monkey: a preferential bias theory.

The functional role of the sensory input to the motor cortex in the execution of voluntary movements is still controversial. We have proposed that the input functions by changing the excitability of cortical efferent columns before and during movements (Asanuma and Arissian, 1984). Experiments were performed to support this hypothesis. Monkeys were trained to sit still in a chair and to pick up a food pellet from a food board rotating at a high speed, so that the subjects had to concentrate their efforts to pick up the pellet. Microelectrode recordings were made from pre- and post-central cortical neurons related to hand movement during the pickup task. It was found that neurons in the motor (10%) and in the sensory (5%) cortices started discharging far ahead of actual movement of the hand. EMGs in the target muscles, which were identified by microstimulation at the recording sites, revealed that some muscles changed their tone during these premovement discharges, although there were no visible movements of the hand. Section of the dorsal columns abolished the premovement discharges and also produced retardation of motor skills. The results supported the hypothesis that circulation of impulses between the cortical efferent columns and the periphery before the movement plays an important role in the execution of skilled movements.