Abstract
Trigeminal somatosensory evoked potentials (SEPs) were recorded from the scalp (A), the skull (B), the dura (C) and from the cortical surface (D) in compliance with the International 10-20 system in cats anesthetized with ketamine and immobilized with pancronium bromide. SEP amplitude decreased most when the recording sites moved from C to B and had the largest spread on A. The intracortical distribution of evoked potentials was also examined at the area where the largest SEP value was obtained. With stimulation of the whisker pad, SEP's early positive wave (P) changed reversely to a deep negative wave (Nd) at the deep layers of the cortex, showing the largest amplitude at a depth of about 1.0 mm from the cortical surface. The amplitude then started to diminish as the electrode was inserted into the deeper layers. Conversely, a negative wave (N) following P, showed the largest amplitude just on the surface of the cortex.
