The effects of hippocampal aspiration lesions on conditioning to the CS and to a background stimulus in trace conditioned suppression.

Rats with hippocampal aspiration lesions or cortical control lesions were compared to sham operated controls in a trace conditioned suppression task, in which a long-lasting background stimulus played the role of more conventional contextual cues. In all three surgical treatment groups, conditioning to the explicit conditioned stimulus (CS) decreased, but conditioning to the background cue increased, when a longer trace interval was used. There was thus no evidence of a differential partitioning of associative conditioning as a result of the lesion, despite the evident sensitivity of the behavioural paradigm to variations in the CS-->unconditioned stimulus (US) interval. This result contrasts with earlier reports using conventional contextual cues in analogous experimental designs, and so suggests that the sensitivity of contextual conditioning to hippocampal dysfunction depends at least in part on the physical nature of conventional contextual cues, and not solely on the less precise predictive information that such cues typically provide.