Simultaneous electroencephalography and functional magnetic resonance imaging of primary and secondary somatosensory cortex in humans after electrical stimulation.

Simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) measurements were performed in six healthy subjects to determine the representation of stimulation of the right thumb in somatosensory cortex. In all subjects EEG-based dipole locations could be determined in primary (S1) and secondary (S2) somatosensory cortex. The stimulus-induced blood oxygenation level dependent response of the fMRI showed deviations of 23.5 mm (standard deviation, SD = 6.9) for S1 and 15.7 mm (SD = 3.5) for S2 cortex. fMRI constrained dipole searches lead to higher residual variances. The data show that simultaneous EEG and fMRI measurements of somatosensory activity are feasible and yield reliable and valid results. Copyright 2002 Elsevier Science Ireland Ltd.