Magnetic detection of sleep spindles in normal subjects.

The magnetoencephalogram (MEG) and electroencephalogram (EEG) were recorded simultaneously from 3 normal subjects during light sleep. The extracranial magnetic field patterns associated with the ionic currents within the brain (MEG) were measured using a SQUID magnetometer in a magnetically shielded room. Although a previous report indicated that there are few sleep spindles in MEG records, we observed many in all 3 subjects. We believe this is because measurements were made vertically at the vertex region.