FOCAL BRAIN-STIMULATION IN HEALTHY HUMANS - MOTOR MAPS CHANGES FOLLOWING PARTIAL HAND SENSORY DEPRIVATION

Cortical motor maps of first dorsal interosseus (FDI), abductor digiti minimi (ADM) and wrist flexors muscles were produced following transc ranial focal magnetic stimulation of the contralateral motor areas in seven volunteers. Motor evoked potentials (MEPs) were recorded before and during median and radial nerves anaesthetic block at wrist. Result s indicated that the FDI muscle cortical representation was significan tly reduced; this muscle was entirely 'enveloped' in the hand region d eprived of its cutaneous sensory information, despite maintaining its usual proprioceptive feed-back and strength via the ulnar nerve. On th e contrary, the ADM (serving as 'control condition' because outside th e anaesthetised hand area) cortical representation was unchanged, even if showing a tendency to enlarge in the topographic maps. No amplitud e changes of compound muscle action potentials of ADM and FDI during p eripheral stimulations were observed, while changes in F-wave response s were detected in both muscles. No significant topographic changes we re found for the wrist flexors muscles. A possible explanation for the se 'short term' rearrangements of brain motor maps is given on the bas is of neural plasticity mechanisms due to the loss of tonic cutaneous inputs on cortical and spinal motoneurons.