dc Magnetoencephalography: Direct measurement in a magnetically extremely-well shielded room

Direct measurement of slow brain activity in the range of seconds is reported. The measurements were made by superconducting quantum interference devices operating in a magnetically extremely well-shielded room. Directly measured dc magnetoencephalography (MEG) reveals that sustained fields of the brain rise with a sharp slope immediately after motor stimulation, whereas their relaxation to the resting level is slower and is delayed by several seconds. These features of sustained brain activity could not be resolved by modulated dc MEG which was applied earlier to study these phenomena. (C) 2004 American Institute of Physics.