Nonreversibility of the appetitive characteristics of intracranial stimulation

¹ Merck Institute for Therapeutic Research, West Point, Pennsylvania

Stainless steel electrodes were implanted in the vicinity of the medial forebrain bundle of monkeys. The monkeys were trained to lever press on an appetitive schedule to receive intracranial stimulation, and on an aversive schedule to avoid a foot shock which was preceded by a warning signal. The lever pressing behavior on the avoidance schedule was extinguished and brain stimulation was substituted as the punishment in the aversive situation. None of the monkeys avoided or escaped the 15-second brain shock. Even when the time period was prolonged to 1 hour, no avoidance behavior occurred. The results indicated that the nature of the intracranial stimulation for the electrode site used was not reversible from appetitive to aversive either with a change in the experimental situation or with a prolongation of the stimulus duration.