SPATIAL PROPERTIES AND INTERHEMISPHERIC DIFFERENCES OF THE SENSORY HAND CORTICAL REPRESENTATION - A NEUROMAGNETIC STUDY

We performed a neuromagnetic investigation of the sensory hand cortica l representation in the two hemispheres of 20 healthy volunteers. The localizations within the brain hemispheres of the cortical Equivalent Current Dipoles (ECDs) activated with the shortest latencies (N20 m an d P30 m components) by separate stimulation of contralateral median ne rve, thumb and little finger were analysed. The ECD spatial coordinate s were in agreement with the known somatotopy of the sensory homunculu s: little finger more medial and posterior, thumb more lateral and ant erior, median nerve in-between. By considering the ECDs to thumb and l ittle finger stimulation the boundaries of the hand cortical represent ation in primary sensory cortex, the 'hand extension' was evaluated as the distance between the two. This parameter was similar on the two h emispheres, the 'hand extension' being 17 mm and 12 mm for N20 m and P 30 m components, respectively, with a standard deviation of 5 mm. We p rovide for the first time the ECDs localization of left and right medi an nerve, thumb and little finger, as well as the 'hand extension' val ues, and their interhemispheric differences as a normative data set de scribing the organization of primary sensory cortical areas reserved t o the hand in the healthy population. This approach permits objective measurements of absolute values, as well as of interhemispheric differ ences, of the sensory hand area following a monohemispheric lesion as well as to non-invasively follow-up its reorganization during clinical recovery. (C) 1997 Elsevier Science B.V.