Lesions of the rat perirhinal cortex spare the acquisition of a complex configural visual discrimination yet impair object recognition.

Abstract

Rats with perirhinal cortex lesions were sequentially trained in a rectangular water tank on a series of 3 visual discriminations, each between mirror-imaged stimuli. When these same discriminations were tested concurrently, the rats were forced to use a configural strategy to solve the problems effectively. There was no evidence that lesions of the perirhinal cortex disrupted the ability to learn the concurrent configural discrimination task, which required the rats to learn the precise combination of stimulus identity with stimulus placement (“structural” learning). The same rats with perirhinal cortex lesions were also unimpaired on a test of spatial working memory (reinforced T maze alternation), although they were markedly impaired on a new test of spontaneous object recognition. For the recognition test, rats received multiple trials within a single session in which on every trial, they were allowed to explore 2 objects, 1 familiar, the other novel. On the basis of their differential exploration times, rats with perirhinal cortex lesions showed very poor discrimination of the novel objects, thereby confirming the effectiveness of the surgery. The discovery that bilateral lesions of the perirhinal cortex can leave configural (structural) learning seemingly unaffected points to a need to refine those models of perirhinal cortex function that emphasize its role in representing conjunctions of stimulus features.

New behavioral protocols to extend our knowledge of rodent object recognition memory

“…Furthermore, because each object serves as both a novel and a familiar stimulus, the protocol counteracts the variance associated with individual object preferences. Experiment 1 (light) produced mean D1 scores ranging from 40-80 sec and mean D2 scores ranging from 0.3-0.4 (depending on strain) for a single 20-min session (see also Aggleton et al 2010;Albasser et al 2010;Horne et al 2010). These D1 are higher than those often achieved after combining two sessions to ensure side counterbalancing (also 20 min of testing) in the standard spontaneous exploration task (D1 ranging from 10-20 sec in Ennaceur and Delacour [1988]; Dix and Aggleton [1999]).…”

BDNF controls object recognition memory reconsolidation

“…We defined exploration as sniffing or touching the stimuli objects with the muzzle and/or forepaws. A discrimination index (DI = (Time exploring novel object À Time exploring familiar object)/Total object exploration time) was used as a measure of discrimination between familiar and novel objects (Aggleton, Albasser, Aggleton, Poirier, & Pearce, 2010;Aubele, Kaufman, Montalmant, & Kritzer, 2008;Langston & Wood, 2010;Cohen et al, 2008;Till et al, 2015). DI varies between À1 and +1.…”

Spontaneous object recognition memory in aged rats: Complexity versus similarity

“…These findings might be consistent with previous results emphasizing the relevance of ambiguity to explain SOR deficits using complex objects. It should be noted that feature ambiguity is maximized in discriminations involving complex objects (Aggleton et al 2010). However, it also should be present in Experiment 2 since it cannot be solved by a particular feature (one plane), requiring the unique combination of planes in each pyramid.…”