Effects of premotor cortex cooling upon visually initiated hand movements in the monkey.

The premotor cortex was temporarily impaired with a local cooling method and effects of the cooling upon visually initiated hand movement and upon cortical field potentials associated with the movement were examined in the monkey. Bilateral cooling of the premotor cortex (the dorsolateral part of presumed area 6) disorganized the well-trained reaction-time movement, in which a lever was lifted within duration of the light stimulus (about 0.5 s) delivered at random time intervals. Accordingly the monkey showed nearly self-paced, random movements with little regard to the light stimulus during the cooling. To obtain a certain number of appropriate reaction-time movements, about twice as many as trials in normal conditions were required during the premotor cooling. Unilateral (contralateral to the moving hand) cooling of the premotor cortex produced similar but weak effects. No appreciable paresis was observed by cooling. Such effects of cooling the premotor cortex faded in successive experimental days of several weeks or even in successive cooling sessions on the same day. This was in contrast with effects of motor cortex cooling which were reported to be almost unfaded on repetition. It is suggested that compensatory actions are quickly elicited in some other structures even on temporal impairment of the premotor cortex and that the actions are gradually accumulated on repetitive cooling with days and weeks.