Elaboration of conditioned alimentary reflexes having different probabilities of reinforcement in rats with hippocampal lesions.

A motor alimentary conditioned reflex was elaborated in hippocampectomized and intact albino rats. Food reinforcement followed 100 percent, 50 percent, 33 percent or 25 percent of conditional stimulus presentations (click from a rotating food box). No differences were found in the rate of conditioned alimentary reflex elaboration between the hippocampectomized and control rats at 100 percent and 50 percent reinforcement, although the time-courses of formation of the conditioned reflex connection differed substantially. With low reinforcement probabilities (33 percent and 25 percent) the operated rats, unlike the intact ones, exhibited no adequate responses throughout the 10 experimental days. The results obtained corroborate an earlier suggestion that the hippocampus is involved in the organization of behavior the reinforcement probability of which is unknown or relatively low.