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

Damage to the perirhinal cortex (PRh) in rats impairs anterograde object-recognition memory after retention intervals of up to several hours, but there is little direct evidence to link PRh function to object-recognition abilities after substantially longer intervals that span several days or weeks. We assessed the effects of PRh lesions on anterograde object recognition using a novel-object preference test, with retention intervals lasting 24 h and 3 weeks. The rats received multiple exposures to the sample object during the learning phase--5 min per day on 5 consecutive days. Control rats displayed a significant novel-object preference after both retention intervals, indicating recognition of the sample object, whereas the rats with PRh lesions displayed a significant preference after the 24-h interval, but not after the 3-week interval. When the learning phase of the trial was shortened to a single 5-min session, the PRh group was impaired in the 24-h condition. The findings indicate that the disruptive effects of PRh damage on anterograde object recognition persist over very long postlearning intervals. The results indicate further that object recognition impairments following PRh damage are not ubiquitous, and that learning conditions play a significant role in determining the subsequent recognition performance in rats with PRh damage.