D9 Magnetoencephalography (MEG)

Topic

The magnetic field recorded by magnetoencephalography originates from the same intracellular dipole currents that produce the electroencephalogram signal. Unlike the electroencephalogram signal, however, the magnetic field is not distorted as it passes through the heterogeneous conductivity of the skull and scalp; this allows magnetoencephalography to offer more precise source localization than the electroencephalogram signal, with particular sensitivity to sources oriented tangentially to the sensor.

Reconstruction of cortical activity from this magnetic field is typically achieved through spatial filtering techniques, which estimate the optimal combination of magnetic field sensors at each point in space. This optimal sensor combination minimizes the variance of unwanted magnetic field sources without distorting the source of interest—that is, without distorting the cortical activity being reconstructed.

Furthermore, the magnetic field recorded by magnetoencephalography combines very high temporal resolution—limited only by the magnetic field sampling rate—with spectral and phase-connectivity analyses analogous to those applied to the electroencephalogram signal, yet with superior spatial resolution due to the magnetic field's more precise source localization.

Ultimately, it is this very magnetic field—generated by the same intracellular dipole currents that produce the electroencephalogram signal, but free from the distortion caused by the heterogeneous conductivity of the skull and scalp—that enables magnetoencephalography to combine more precise source localization, very high temporal resolution, and better spatial resolution than the electroencephalogram signal, all within the same types of spectral and phase-connectivity analyses shared by both techniques.

ID:4305