Changes in corticomotor representations induced by prolonged peripheral nerve stimulation in humans

Objective: Manipulation of afferent input can induce reorganization within the sensorimotor cortex which may have important functional consequences. H ere we investigate whether prolonged peripheral nerve stimulation can induc e reorganization within the human motor cortex. Methods: Using transcranial magnetic stimulation, we mapped the scalp repre sentation of the corticospinal projection to hand muscles in 8 normal subje cts before and after 2 h of simultaneous repetitive electrical stimulation of the ulnar and radial nerves at the wrist. Control mapping experiments we re conducted in 6 subjects. Results: Following nerve stimulation, larger motor-evoked potentials were e voked from more scalp sites. The induced changes were most apparent in firs t dorsal interosseous, but were also seen in other hand muscles. The increa ses in area of the representational maps were accompanied by changes in the location of the optimal site for evoking responses in first dorsal interos seous, and changes in the centres of gravity of the maps. Conclusions: Prolonged afferent stimulation induces an increase in excitabi lity of the corticospinal projection. This is accompanied by a significant shift in the centre of gravity of the stimulated muscles which we propose i s evidence of a non-uniform expansion in their cortical representation. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.