Training-induced recovery of manual dexterity after a lesion in the motor cortex.

Cerebral injury, such as stroke, cause functional deficits; however some functions can recover with postlesion rehabilitative training. Several recent studies using rodents and monkeys have reported the effects of postlesion training on functional recovery after brain injury. We present herein an overview of recent animal experimental studies on the effects of postlesion motor training on brain plasticity and motor recovery. Our study in the macaque monkey reported the effects of hand motor training on motor recovery after lesioning of the primary motor cortex (M1). In monkeys that had undergone intensive daily training after the lesion, manual dexterity recovered to previous levels. Relatively independent digit movements, including those of precision grip, were restored in the trained monkeys. While hand movements recovered to some extent in the monkeys without postlesion training, these monkeys frequently used alternative grips to grasp a small object instead o f the precision grip. These findings suggest that recovery after M1 lesions includes both training-dependent and training-independent processes, and that recovery of precision grip requires intensive postlesion training. Recent results of both brain imaging and gene expression analyses suggest that functional and structural changes may occur in uninjured motor areas during recovery of hand function after M1 lesions. In particular, our preliminary results suggest that structural changes in ventral premotor cortex neurons may participate in functional compensation of precision grip.