Biomagnetism

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.

Measurements of the brain's magnetic field, called magnetoencephalograms (MEG's), have been taken with a superconducting magnetometer in a heavily shielded room. This magnetometer has been adjusted to a much higher sensitivity than was previously attainable, and as a result MEG's can, for the first time, be taken directly, without noise averaging. MEG's are shown, simultaneously with the electroencephalogram (EEG), of the alpha rhythm of a normal subject and of the slow waves from an abnormal subject. The normal MEG shows the alpha rhythm, as does the EEG, when the subject's eyes are closed; however, this MEG also shows that higher detector sensitivity, by a factor of 3, would be necessary in order to clearly show the smaller brain events when the eyes are open. The abnormal MEG, including a measurenment of the direct-current component, suggests that the MEG may yield some information which is new and different from that provided by the EEG.