Thalamic negativity associated with the endogenous late positive component of cerebral evoked potentials (P300): recordings using discriminative aversive conditioning in humans and cats.

Electrical potentials within the thalamus associated with the endogenous late positive component (LPC or P300) of cerebral evoked potentials were investigated in humans and cats. Essentially identical discrimination tasks using classical aversive conditioning were employed for recording LPC in both species. In humans, a negative wave within the same latency range as that of LPC was noted, with dependency on stimulus-relevance, at all thalamic and mesencephalic recording sites which included the nucl. centrum medianum, nucl. parafascicularis, and periaqueductal gray. Similar negative waves were also observed over wide areas of the thalamus of cats including specific as well as non-specific thalamic nuclei. The negative waves seen in the thalamus were generally higher in amplitude than those seen in the white matter and became unclear when the electrodes penetrated the ventral border of the thalamus.