Localization of evoked neuromagnetic 600 Hz activity in the cerebral somatosensory system.

Upon electrical median nerve stimulation wide-band scalp SEP recordings show a burst of high-frequency low-amplitude wavelets of uncertain origin. Digital high-pass filtering (above 400 Hz) of the primary cortical response ("N20") can separate the burst from the underlying "N20 proper" which itself is known to be generated by excitatory postsynaptic potentials (EPSPs) in area 3b. Here, neuromagnetic multichannel recordings show a close correlation between the spatial field distributions of the magnetic burst and of the magnetic "N20m" proper.