76 ©1998 Elsevier Scie

Background. This study is an attempt to combine and compare EEG, MEG and functional magnetic resonance imaging (FMRI) methods to map the somatotopic organization of primary somatosensory cortex. Methods. 32-channel EEG and 143-channel MEG recordings were acquired from two subjects during tactile stimulation of the fingertips. In addition, FMRI activation maps were produced during fingertip vibration and finger movements. Dipole analysis was used to calculate source location and confidence regions for the EEG and MEG responses which were compared to the FMRI activation maps. Results. The 50 ms response in the averaged EEG and MEG data could be modeled as an equivalent current dipole in the postcentral gyrus with the expected somatotopic organization. 95% confidence regions indicated that sources for individual digits can be discriminated with sufficient signal-to-noise ratio. Conclusions. The results indicated that the somatotopic organization of the somatosensory cortex can be successfully demonstrated using EEG and MEG responses to mechanical stimulation of individual digits. Initial fMRI results suggest that tactile stimulation does not produce robust responses, whereas passive stimulation produced clear activation patterns in the postcentral gyrus in close proximity to the dipole sources for tactile stimulation.,