Lesions of Premotor Cortex in Man

Moderate unilateral weakness of shoulder and hip muscles and limb-kinetic apraxia were observed in 11 patients with frontal lobe lesions on the side opposite to the neurological deficits. On the CT scans, the posterior border of the lesions lay anterior to the precentral gyrus, thus involving the premotor cortex but not the primary motor cortex. In 9 cases, the lesions were caused by a brain infarct, in 2 cases by a tumour. In 1 patient the lesion was purely subcortical. Whereas the paresis affected all hip muscles, in the shoulder mainly those movements associated with abduction and elevation of the arm were disturbed. The EMG showed considerable delays for the preactivation of proximal arm muscles during rapid arm movements, thus interfering with the normal proximal-distal sequencing of muscle action. Limb-kinetic apraxia only became apparent during tasks requiring certain coordinations between both arms or legs. Bimanual interaction was normal. Two patients with proximal hemiparesis and small lesions in the precentral gyrus which have been examined for comparison showed no limb-kinetic apraxia and different distributions of the paretic shoulder girdle muscles. In view of the long-standing controversies as to the functional role of the premotor cortex and the question of specific deficits after lesions of this area, the relevant literature is reviewed.