Double Dissociation between the Effects of Peri-Postrhinal Cortex and Hippocampal Lesions on Tests of Object Recognition and Spatial Memory: Heterogeneity of Function within the Temporal Lobe

Abstract

It is widely believed that declarative memory is mediated by a medial temporal lobe memory system consisting of several distinct structures, including the hippocampus and perirhinal cortex. The strong version of this view assumes a high degree of functional homogeneity and serial organization within the medial temporal lobe, such that double dissociations between individual structures should not be possible. In the present study, we tested for a functional double dissociation between the hippocampus and peri-postrhinal cortex in a single experiment. Rats with bilateral excitotoxic lesions of either the hippocampus or peri-postrhinal cortex were assessed in tests of spatial memory (radial maze) and object recognition memory. For the latter, the spontaneous object recognition task was conducted in a modified apparatus designed to minimize the potentially confounding influence of spatial and contextual factors. A clear functional double dissociation was observed: rats with hippocampal lesions were impaired relative to controls and those with peripostrhinal cortex lesions on the spatial memory task, whereas rats with peri-postrhinal lesions were impaired relative to the hippocampal and control groups in object recognition. These results provide strong evidence in favor of heterogeneity and independence of function within the temporal lobe.

The rat perirhinal cortex: A review of anatomy, physiology, plasticity, and function

“…Double dissociation studies confirmed these findings showing that animals with hippocampal lesions showed impairments in recognition memory but not in spatial memory and those with perirhinal lesions showed impairments in spatial memory but not in recognition memory (Ennaceur et al, 1996;Bussey et al, 2000;Winters et al, 2004). This dissociation between hippocampal and perirhinal function was conserved across rat strains (Futter et al, 2006) and species (Pihlajamä ki et al, 2004;Buckley, 2005;Kö hler et al, 2005).…”

“…Perirhinal lesion studies that do report spatial memory deficits also show some damage to the postrhinal cortex (Mumby and Glenn, 2000;Glenn et al, 2003) or also involve entorhinal cortex lesions (Nagahara et al, 1995). One combined perirhinal and postrhinal lesion study has reported impairments in spatial memory (Liu and Bilkey, 2001) but a number of other combined perirhinal and postrhinal lesion studies showed no deficits in spatial memory Bussey et al, 1999Bussey et al, , 2000Winters et al, 2004).…”

Towards a functional organization of the medial temporal lobe memory system: Role of the parahippocampal and medial entorhinal cortical areas

“…In studies that examine recognition by monitoring spontaneous exploration of familiar and novel stimuli, monkeys with selective hippocampal or parahippocampal cortex damage that show little or no deficit in DNMS have severe and rapidly apparent deficits on the spontaneous novelty exploration task Nemanic et al, 2004). In rats, some studies report no deficit (e.g., Mumby, 2001;Mumby et al, 2002;Winters et al, 2004), whereas other studies have observed impairment at long delays Hammond et al, 2004), or following a large amount of damage to the hippocampus (Broadbent et al, 2004). In contrast to the modest and variable deficit observed following damage to the hippocampus, ablation of the perirhinal cortex consistently results in a severe and rapidly developing deficit in both kinds of recognition memory tasks in monkeys (Nemanic et al, 2004) and in rats (Mumby et al, 2002;Winters et al, 2004;Norman and Eacott, 2005;Winters and Bussey, 2005).…”

Object recognition testing: Methodological considerations on exploration and discrimination measures

“…Furthermore, different test protocols are being used. For example, some studies use flexible sample trial durations, allowing all animals to reach a specific amount of object interaction [12,[30][31][32]. Other experiments have fixed sample trial durations and each individual animal differs in the amount of sample object exposure [1,11,25,33].…”