Perceptual cues of reinforcing brain stimulations in the postero-lateral area of the hypothalamus.

In order to study the perception of intracranial reward in the rat, a rewarding hypothalamic brain stimulation served as conditioned stimulus (CS) in an avoidance paradigm. The rate of self-stimulations behavior was used to estimate the strength of intracranial reward and reinforcement. Tests of stimulus generalization were performed by modifying the electrical parameters of the CS so as to form a set of substitute stimuli (SS). Results show that the discrimination gradient depends mainly on the rewarding value of the intracranial stimulation. A Stevensian power function relates the percentage of avoidance responses to the intensity of the self-stimulation behavior, which in turn was estimated by such methods as continuous reinforcement frequency, fixed ratio schedules, weight, choice, self-regulation and cost methods. Moreover, the latency of the avoidance responses is related directly to the magnitude of the self-stimulation elicited by the same brain stimulations. On grounds of this data, we assume that the internal decisional process could discriminate well between the different brain stimuli on the basis of the rewarding value produced. Differences observed between methods evaluating the magnitude of reinforcement induced by the rewarding electrical brain stimuli are thus mainly due to differences in motor performances required by each method to obtain the electrical reward.