Source Estimation of the K-Complex MEG and Auditory Evoked Fields

This study focuses on electrical brain activities during sleep, particularly on K-complexes in normal subjects during sleep stage 2. We investigated the relationship between the sources of K-complexes and the sources of auditory evoked responses. We analyzed these waveforms on the basis of both topographic electroencephalographic (EEG) and magnetoencephalographic (MEG) maps. The components of magnetic fields perpendicular to the surface of the head were measured using a one-channel dc SQUID with a second-order gradiometer or a seven-channel dc SQUID with a first-order gradiometer, and electric potentials were simultaneously recorded at 14 electrodes. On the basis of the MEG measurement results, the source of K-complexeas can be modeled by two current dipoles. The dipoles are estimated to be at a position 10 mm superior to the sources of N100 components of the auditory evoked responses as estimated from the evoked potentials and magnetic fields. This result suggests that the mechanism of K-complexes is closely related to that of auditory evoked responses.