Somatosensory evoked responses and slow potential oscillations in human scalp recordings.

Average evoked responses obtained from the frontal, parietal and vertex regions, by electrical stimulation of the median nerve or common peroneal nerve, indicate the presence of time locked components which occur as late as 500 to 3500 msec after the stimulus. Spectral analysis shows that these components are distributed mostly in the 1.5 to 2 and 3.6 to 4 Hz frequently bands, and their presence in the evoked response may be due to the driving, by the stimuli of oscillations of similar frequencies which can be seen in the spontaneous activity recorded from the same region.