Activation of multiple cortical areas in response to somatosensory stimulation: Combined magnetoencephalographic and functional magnetic resonance imaging

We combined information from functional magnetic resonance imaging (fMRI) a nd magnetoencephalography (MEG) to assess which cortical areas and in which temporal order show macroscopic activation after right median nerve stimul ation. Five healthy subjects were studied with the two imaging modalities, which both revealed significant activation in the contra- and ipsilateral p rimary somatosensory cortex (SI), the contra- and ipsilateral opercular are as, the walls of the contralateral postcentral sulcus (PoCS), and the contr alateral supplementary motor area (SMA). Ln fMRI, two separate foci of acti vation in the opercular cortex were discerned, one posteriorly in the parie tal operculum (PO), and one anteriorly near the insula or frontal operculum (anterior operculum, AO). The activation sites from fMRI were used to cons train the solution of the inverse problem of MEG, which allowed us to const ruct a model of the temporal sequence of activation of the different sites. According to this model, the mean onset latency for significant activation at the contralateral SI was 20 msec (range, 17-22 msec), followed by activ ation of PoCS at 23 msec (range, 21-25 msec). The contralateral PO was acti vated at 26 msec (range, 19-32 msec) and AO at 33 msec (range, 22-51 msec). The contralateral SMA became active at 36 msec (range, 24-48 msec). The ip silateral SI, PO, and AO became activated at 54-67 msec. We conclude that f MRI provides a useful means to constrain the inverse problem of MEG, allowi ng the construction of spatiotemporal models of cortical activation, which may have significant implications for the understanding of cortical network functioning. (C) 1999 Wiley-Liss, Inc.