Source modeling of MEG and EEG activities evoked by color imagination

The authors propose models in which both magnetoencephalogram (MEG) and electroencephalogram (EEG) activities evoked by color imagination are recorded simultaneously. The components of the magnetic fields perpendicular to the surface of a head were measured by using a DC SQUID with a first-derivative gradiometer. The authors observed that both MEG and EEG activities were affected by color imagination. The power spectrum of the MEG evoked by color imagination showed a single sharp peak at 11 Hz. In contrast, the power spectrum of EEG showed broad patterns. The EEG topography showed that the spectrum component at 11 Hz dominated in the occipital region. On the basis of these results, the authors propose a two-dipole model whose directions vary with time to explain the change in EEG topography evoked by color imagination