Interaction between forced grasping and a learned precision grip after ablation of the supplementary motor area.

Monkeys were trained to compress and release a force transducer held between the thumb and forefinger. Immediately following ablation of the contralateral supplementary motor area a grasp reflex produced a disturbance of the learned precision grip characterized by an increase in mean grasping force, an increase in the rate of prehensile force application and the inability to release the strain gauge. No change was observed in the same learned grip with the ipsilateral hand.