SOMATOTOPY OF HUMAN HAND SOMATOSENSORY CORTEX REVEALED BY DIPOLE SOURCE ANALYSIS OF EARLY SOMATOSENSORY-EVOKED POTENTIALS AND 3D-NMR TOMOGRAPHY

Somatosensory evoked potentials (SEPs) to median nerve and finger stim ulation were analyzed by means of spatio-temporal dipole modelling com bined with 3D-NMR tomography,in 8 normal subjects. The early SEPs were modelled by 3 equivalent dipoles located in the region of the brain-s tem (B) and in the region of the contralateral somatosensory cortex (T and R). Dipole B explained peaks P14 and N18 at the scalp. Dipole T w as tangentially oriented and explained the N20-P20, dipole R was radia lly oriented and modelled the P22. The tangential dipole sources T wer e located within a distance of 6 mm on the average and all were less t han 9 mm from the posterior bank of the central sulcus. In 6 subjects the tangential sources related to finger stimulation arranged along th e central sulcus according to the known somatotopy. The radial sources did not show a consistent somatotopic alignment across subjects. We c onclude that the combination of dipole source analysis and SD-NMR tomo graphy is a useful tool for functional localization within the human h and somatosensory cortex.