A neuromagnetic normative data set for hemispheric sensory hand cortical representations and their interhemispheric differences.

Somatotopy of human hand primary sensory cortex has been studied neuromagnetically [C. Baumgartner, A. Doppelbauer, L. Deecke, D.S. Barth, J. Zeitlhofer, G. Lindinger, W.W. Sutherling, Neuromagnetic investigation of somatotopy of human hand somatosensory cortex, Exp. Brain Res. 87 (1991) 641-648.] [1]. Investigation of sensory cortex devoted to the hand will be of major importance in relation to clinical recovery after sensorimotor deficits as well as an index of plasticity phenomena following alterations of peripheral nerves inputs. Here a normative data set has been constructed, on the basis of the neuromagnetic investigation of the primary sensory hand cortical representation in the two hemispheres of 20 healthy volunteers. This can be used to evaluate interhemispheric differences of the 'sensory' hand areas during experimental paradigms in the healthy as well as following patients with monohemispheric lesions. The localizations in each hemisphere of the cortical Equivalent Current Dipoles (ECDs) activated with the shortest latencies (N20m and P30m components) by separate stimulation of left and right median nerve, thumb and little finger were analysed. By considering the ECDs to thumb and little finger stimulation the boundaries of the hand cortical representation in primary sensory cortex, the 'hand extension' was measured as the distance between the two. For all the considered parameters (related to N20m and P30m ECDs: latency, strength, spatial position in the individual head, 'hand extension', interhemispheric differences) the appropriate variable distribution was considered and by including the 98% of the healthy population normative limits were calculated.