Perirhinal cortex lesions impair tests of object recognition memory but spare novelty detection.

Jeffrey Dalley,Cristian M Olarte‐Sánchez,Eman Amin,E Clea Warburton,John P Aggleton

doi:10.1111/ejn.13106

Jeffrey Dalley, Cristian M Olarte‐Sánchez + Show 3 more

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https://doi.org/10.1111/ejn.13106

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Abstract

The present study examined why perirhinal cortex lesions in rats impair the spontaneous ability to select novel objects in preference to familiar objects, when both classes of object are presented simultaneously. The study began by repeating this standard finding, using a test of delayed object recognition memory. As expected, the perirhinal cortex lesions reduced the difference in exploration times for novel vs. familiar stimuli. In contrast, the same rats with perirhinal cortex lesions appeared to perform normally when the preferential exploration of novel vs. familiar objects was tested sequentially, i.e. when each trial consisted of only novel or only familiar objects. In addition, there was no indication that the perirhinal cortex lesions reduced total levels of object exploration for novel objects, as would be predicted if the lesions caused novel stimuli to appear familiar. Together, the results show that, in the absence of perirhinal cortex tissue, rats still receive signals of object novelty, although they may fail to link that information to the appropriate object. Consequently, these rats are impaired in discriminating the source of object novelty signals, leading to deficits on simultaneous choice tests of recognition.

Highlights

The present study examined why the rat perirhinal cortex is vital for recognition memory, i.e. the ability to detect when a stimulus is repeated
Perirhinal cortex lesions in rats are presumed to impair recognition memory, as demonstrated by deficits on delayed non-matching-tosample problems (Mumby & Pinel, 1994), and the difficulty observed in discriminating novel from familiar objects in spontaneous preference tests (Brown, 1996; Ennaceur et al, 1996; Winters et al, 2008; Warburton & Brown, 2010; Kinnavane et al, 2015)
Two different explanations have been given for why perirhinal cortex lesions can spare this example of novelty detection, but impair the subsequent test phase, when rats are selecting between one novel and one familiar object

Summary

Introduction

The present study examined why the rat perirhinal cortex is vital for recognition memory, i.e. the ability to detect when a stimulus is repeated. The rationale arose from the finding that perirhinal cortex lesions consistently impair the spontaneous discrimination of a novel object from a familiar object (Ennaceur et al, 1996; Dere et al, 2007; Winters et al, 2008; Warburton & Brown, 2015) Such tests are based on the preferential exploration of novel objects. Ennaceur et al, 1996; Aggleton et al, 1997; Moran & DalrympleAlford, 2003; Winters et al, 2004; Barker et al, 2007; Bartko et al, 2007a,b; Mumby et al, 2007; Albasser et al, 2009, 2015; McTighe et al, 2010) Such behaviour during the sample phase suggests normal detection of novelty, but this seemingly spared ability contrasts with the discrimination deficit found in the subsequent spontaneous novelty preference test

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