Selective hippocampal lesions impair acquisition of appetitive trace conditioning with long intertrial and long trace intervals.

Whereas hippocampal lesions clearly impair performance on aversive trace conditioning tasks, recent evidence suggests that such lesions do not affect performance on appetitive trace conditioning tasks with trace intervals from 2 seconds up to 20 seconds. The current study first demonstrated that intact rats can learn trace conditioning tasks with longer trace intervals (8 s) when the average intertrial interval (intertrial interval [ITI]) was lengthened from 150-s to 300-s. In two subsequent experiments with longer ITIs (420-s and 825-s), hippocampal-lesioned rats performed similarly to intact controls in an appetitive trace conditioning task with 20-s trace interval but were impaired in an appetitive trace conditioning task with a 60-s trace interval. These results suggest that the training ITI and the trace interval are important variables to consider in appetitive trace conditioning, and the hippocampus may play an important role in appetitive trace conditioning when the ITI and trace intervals are both sufficiently long.