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PubMed1974

On the role of the hippocampus in the integrative activity of the brain.

The present evidence plus data from the literature suggest that the hippocampus is concerned with responses to signals having low probability of reinforcement. The theta-rhythm, characteristic of the hippocampus, arises in a situation of pragmatic uncertainty, when stereotypical behavioral patterns have not yet been formed and when decisions are still being sought. The theta-rhythm may serve as a correlate only of orienting-exploratory responses and not as a correlate of the orienting-defensive responses of "biological alertness", in Pavlov's terminology. Functionally, the hippocampus belongs to the system of structures which make decisions about the response to a given stimulus. If, following destruction of the hippocampus, the neocortex gives preference to signals with high probability of reinforcement and in the sphere of unconditioned responses a stronger motivation is predominant, then hippocampal involvement is essential for simultaneous assessment of these two factors. For that reason, the hippocampus plays an important role in the competition among conditioned reflexes having different magnitudes and reinforcement probabilities.

Animals↗
PubMed1974

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.

Acoustic Stimulation↗