The cognitive P40, N60 and P100 components of somatosensory evoked potentials and the earliest electrical signs of sensory processing in man.

Selective attention tasks involving random sequences of electrical stimulation of fingers were designed to compare cerebral potentials to identical stimuli (for example to the left thumb) when they are 'infrequent target' signals or 'frequent-neglected' signals in the series. The experiments were carried out in normal adult subjects. The early SEP components were analyzed for the earliest cortical electrical sign of information processing stages. Two new components, P40 (with onset at 26 msec) and N60, precede the processing positivity P100 which may be more significant in somatosensory processing than the negativities recorded in auditory or visual tasks.