Study on Auditory Evoked Responses in Monkeys

Abstract

This investigation was carried out to study auditory cortical responses that could be recorded from the scalp, dura and brain of the rhesus monkeys.
In the alert monkey the averaged cortical response with the early wave components (P₁ and N₁) being the largest and most consistent, could be recorded from the scalp near the vertex and was maximally recorded from the precentral dura.
During anesthesia the averaged cortical response could be maximally recorded from the dura over the middle portion of the superior temporal lobe. Compared with the alert state the P₁ and N₁ waves greatly diminished in amplitude during anesthesia, but did not change significantly in latency. On the other hand, the P₂ and N₂ waves greatly increased in amplitude and became longer in latency.
In the alert state, scalp response thresholds were poorer than intracranial ones. Intracranial response thresholds were lowest during sedation with phencyclidine hydrochloride and progressively became worse during the anesthetized state and highest in the alert state.