Magnitude of the object recognition deficit associated with perirhinal cortex damage in rats: Effects of varying the lesion extent and the duration of the sample period.

Abstract

The present study examines 2 factors that might moderate the object-recognition deficit seen after perirhinal cortex damage. Object recognition by normal rats was improved by extending (from 4 to 8 min) the sample period during which an object was first explored. Furthermore, there was a significant positive correlation between time spent in close exploration of the sample object and degree of successful novelty discrimination. In contrast, rats with perirhinal cortex lesions failed to benefit from increased close exploration and did not discriminate the novel object after even the longest sample period. Nevertheless, the lesions did not disrupt habituation across repeated exposure to the same object. The second factor was extent of perirhinal cortex damage. A significant correlation was found between total perirhinal cortex loss and degree of recognition impairment. Within the perirhinal cortex, only damage to the caudal perirhinal cortex correlated significantly with recognition memory deficits. This study highlights the critical importance of the perirhinal cortex within the temporal lobe for recognition memory and shows that the lesion-induced deficit occurs despite seemingly normal levels of close object exploration.

Object recognition testing: Methodological considerations on exploration and discrimination measures

“…Furthermore the property of one-trial learning makes it suitable for the examination of temporal aspects of memory. Over time, it has become a widely used tool for the assessment of memory functions in combination with pharmacological treatments [6][7][8][9][10] and brain lesions [11][12][13][14]. The ORT is mainly used for rodent experiments, most research is done with rats and mice but the task is also suitable for testing other rodent species [15].…”

“…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]. Before testing starts, the animals are often familiarized or habituated and protocols differ greatly between laboratories.…”

“…Before testing starts, the animals are often familiarized or habituated and protocols differ greatly between laboratories. In some laboratories the animals are allowed to familiarize with only the apparatus [2,11,12,23], others also introduce objects in the pre-experimental phase [25] or even let the animals undergo the full testing procedure, including injections [34,35]. Even more fundamental, there is no consensus about the definition of object investigation.…”

“…In the original test, object investigation was defined as directing the nose towards the object at a distance of 2 cm or less [1]. However, also minimal proximities of 1 cm [11] and 4 cm [2] have also been reported. Generally, climbing and leaning on objects is not considered to be object examination [36], although some do in fact consider this to be relevant object-directed behaviour [2,37,38].…”

Unraveling the contributions of the diencephalon to recognition memory: A review

“…In the rat, unlike the monkey, structures such as the medial dorsal nucleus receive few, if any, projections from the perirhinal cortex (Groenewegen 1988). If the rat is predominantly reliant on perirhinal familiarity-based processes for standard tests of object recognition, then it is likely that temporal lobe functions are largely sufficient (Mumby and Pinel 1994;Albasser et al 2009Albasser et al , 2010, as the rat perirhinal cortex cannot access the medial diencephalon. Consistent with this interpretation, immediate-early gene imaging studies have found increased c-fos activity for novel visual stimuli in the perirhinal cortex but not in the medial dorsal thalamic nucleus (Zhu et al 1995).…”