The hippocampus and conditioning to contextual cues.

Two experiments are reported in which behavioral control by contextual cues was assessed in groups of rats with dorsal hippocampal (HC), neocortical (NC), or operated control (OC) lesions. Following Odling-Smee's (1975) procedure, a Pavlovian conditioning paradigm was followed in which conditioned stimuli (CSs: tone, light) predicted an unconditioned stimulus (US:footshock) always, never, or half the time. Conditioning trials took place in a small black box. Subsequently, conditioning to background contextual cues was assessed by measuring the amount of time rats spent in the black box in preference to an adjacent white one with neither CS nor US presented. In OC groups and, to a lesser extent, NC groups, conditioning to background cues was inversely related to the probability that CS predicted US. In contrast to graded contextual conditioning in control groups, the HC groups consistently showed abnormally strong conditioning to context that was at or near asymptotic level. The results, which were related to current theories of the relation between contextual stimuli and CSs, suggest that the hippocampus may play an important role in stimulus selection during learning.