Hippocampal damage and anterograde object-recognition in rats after long retention intervals.

Although several studies in rats have found that hippocampal damage has negligible effects on anterograde object-recognition memory, the findings are not entirely conclusive, because most studies have used retention intervals lasting only a few hours. We assessed the effects of neurotoxic hippocampal lesions on anterograde object recognition, using a novel-object preference test, with retention intervals that were considerably longer than in previous studies-24 h, 1 week, and 3 weeks. To promote object recognition after such long intervals, rats were familiarized with a sample object in an open field for 5 min/day for 5 consecutive days. Recognition was assessed by comparing the amount of time spent investigating the sample versus a novel object on a preference test at one of the postlearning intervals. The rats with hippocampal lesions displayed a normal novelty preference after a 3-week interval, and their performance across the three delay conditions was not significantly different from that of control rats. The findings indicate that extensive hippocampal damage spares anterograde object recognition in rats, even after retention intervals lasting days or weeks.