[Evoked potential asymmetry in the motor cortex of Macaca fascicularis monkeys during instrumental reflex...

The monkeys were trained to draw a lever by the left or right hand. Cortical motor evoked potentials (MEP) exhibited the highest amplitude in the cortical motor representation of the "working" hand during the period of learning. The extent of interhemispheral asymmetry of the MEP was the same during operation by the left and right hands. After formation of the conditioned reflex, the interhemispheral asymmetry was significantly less during manipulation by the left hand than by the right one. The decrease of asymmetry was due to relatively high amplitude of the MEP in the left hemisphere during instrumental manipulation of both the right and left hands. The data obtained indicate the formation of functional differences in symmetrical motor areas of the cortex in monkeys during their symmetrical instrumental conditioning by the left and right extremities.