Magnetoencephalography: evidence of magnetic fields produced by alpha-rhythm currents.

Weak alternating magnetic fields outside the human scalp, produced by alpha-rhythm currents, are demonstrated. Subject ard magnetic detector were housed in a multilayer magnetically shielded chamber. Background magnetic noise was reduced by signal-averaging. The fields near the scalp are about 1 x 10(-9) gauss (peak to peak). A course distribution shows left-right symmetry for the particular averaging technique used here.