Available online at www.sciencedirect.com Behavioural Brain Research 185 (2007) 82–87 Research report Perirhinal cortex damage and anterograde object-recognition in rats after long retention intervals Dave G. Mumby a,∗ , Pavel Piterkin a , Valerie Lecluse a , Hugo Lehmann b a Center for Studies in Behavioural Neurobiology, Department of Psychology, SP-244, Concordia University, 7141 Sherbrooke St. W., Montreal, Quebec H4B 1R6, Canada b Canadian Centre for Behavioural Neuroscience, The University of Lethbridge, Canada Received 30 November 2006; received in revised form 10 July 2007; accepted 15 July 2007 Available online 21 July 2007 Abstract 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—5min 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. © 2007 Elsevier B.V. All rights reserved. Keywords: Nonspatial memory; Object recognition; Novelty preference; Exploratory behavior; Open field Object-recognition memory is the ability to discriminate between objects that have been previously encountered and objects that have not. This ability is often impaired in patients with medial temporal-lobe damage affecting the hippocampus (HPC) and various parahippocampal cortical areas, including the entorhrinal cortex, parahippocampal gyrus, and perirhinal cortex (PRh). Much evidence suggests the PRh is the most important temporal-lobe structure for object recognition. Dam- age to the PRh impairs performance on tests of anterograde object-recognition memory in rats and monkeys [1–8], whereas, damage limited to the HPC typically spares anterograde object- recognition, at least in rats [9]. A significant number of PRh neurons display diminished responses following presentation of familiar objects as compared to novel objects, but such firing characteristics are uncommon among HPC neurons [10–13]. ∗ Corresponding author. Tel.: +1 514 848 2424x2233; fax: +1 514 848 4545. E-mail address: david.mumby@concordia.ca (D.G. Mumby). Our current understanding of the cellular and molecular mechanisms that underlie memory distinguishes between pro- cesses supporting relatively short-lasting versus long-lasting memories. Some of the processes that support short-lived memo- ries are initiated within milliseconds of an experience and persist for only a few seconds, minutes, or hours. Processes that support long-lasting memories take a relatively long time to transpire, requiring several minutes, hours, or days. Most evidence linking the PRh to object recognition comes from studies that examined relatively short-term processes. For example, studies reporting decreased responsiveness of PRh neurons to repeated presenta- tion of objects have generally been limited to recording periods of less than an hour, although some have employed interpresen- tation intervals as long as 24 h [13]. Most lesion studies have assessed anterograde recognition after retention intervals last- ing minutes or hours, and only a few have used intervals as long as 24 h. Accordingly, there is limited data on the role of PRh in supporting object-recognition memory at intervals that unam- biguously require long-term (i.e., protein-synthesis dependent) representations—intervals spanning days or weeks. The purpose 0166-4328/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.bbr.2007.07.026