Non-invasive long-term recordings of cortical 'direct current' (DC-) activity in humans using magnetoencephalography

Recently, biomagnetic fields below 0.1 Hz arising from nerve or muscle inju ry currents have been measured noninvasively using superconducting quantum interference devices (SQUIDs), Here we report first long-term recordings of cortical direct current (DC) fields in humans based on a horizontal modula tion (0.4 Hz) of the body and, respectively, head position beneath the sens or array: near-DC fields with amplitudes between 90 and 540 fT were detecte d in 5/5 subjects over the auditory cortex throughout prolonged stimulation periods (here: 30 s) during which subjects were listening to concert music . These results prove the feasibility to record non-invasively low amplitud e near-DC magnetic fields of the human brain and open the perspective for s tudies on DC-phenomena in stroke, such as anoxic depolarization or periinfa rct depolarization, and in migraine patients. (C) 1999 Elsevier Science Ire land Ltd, All rights reserved.