The hippocampal formation as a source of the slow endogenous potentials.

Magnetic fields were detected with a SQUID sensor at the temporal and occipital areas of the head in response to a frequent and an infrequent attended visual stimulus. The time-course of the magnetic field for the infrequent stimulus correlated highly with the simultaneously measured electrical potential that showed the commonly observed N2-P3 complex. Analysis of the pattern of the magnetic field showed that the sources of N2 and P3 lay deep in the brain within the hippocampal formation.