Source analysis of MEG activities during sleep (abstract)

S. Ueno, K. Iramina

Research output: Contribution to journalArticlepeer-review


The present study focuses on magnetic fields of the brain activities during sleep, in particular on K complexes, vertex waves, and sleep spindles in human subjects. We analyzed these waveforms based on both topographic EEG (electroencephalographic) maps and magnetic fields measurements, called MEGs (magnetoencephalograms). The components of magnetic fields perpendicular to the surface of the head were measured using a dc SQUID magnetometer with a second derivative gradiometer. In our computer simulation, the head is assumed to be a homogeneous spherical volume conductor, with electric sources of brain activity modeled as current dipoles. Comparison of computer simulations with the measured data, particularly the MEG, suggests that the source of K complexes can be modeled by two current dipoles. A source for the vertex wave is modeled by a single current dipole which orients along the body axis out of the head. By again measuring the simultaneous MEG and EEG signals, it is possible to uniquely determine the orientation of this dipole, particularly when it is tilted slightly off axis. In sleep stage 2, fast waves of magnetic fields consistently appeared, but EEG spindles appeared intermittently. The results suggest that there exist sources which are undetectable by electrical measurement but are detectable by magnetic field measurement. Such source can be described by a pair of opposing dipoles of which directions are oppositely oriented.

Original languageEnglish
Pages (from-to)6023
Number of pages1
JournalJournal of Applied Physics
Issue number8
Publication statusPublished - Apr 15 1991

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy


Dive into the research topics of 'Source analysis of MEG activities during sleep (abstract)'. Together they form a unique fingerprint.

Cite this