Source analysis of spontaneous MEG activities in human subjects during sleep

This study focuses on neuromagnetic approaches to the detection of the brain electrical activities which are difficult to detect by EEG measurements. Sources of the delta waves in human subjects during sleep were investigated in the time and frequency domains. Both EEG and MEG activities were recorded simultaneously. The components of magnetic fields perpendicular to the surface of the head were measured using a SQUID. We observed that the frequency distributions were different for delta waves measured by MEG and EEG recordings. This frequency shift suggests that the sources which generate the magnetic fields are different from those which produce the EEG.