Abstract
Findings of pharmacological studies that have investigated the involvement of specific regions of the brain in recognition memory are reviewed. The particular emphasis of the review concerns what such studies indicate concerning the role of the perirhinal cortex in recognition memory. Most of the studies involve rats and most have investigated recognition memory for objects. Pharmacological studies provide a large body of evidence supporting the essential role of the perirhinal cortex in the acquisition, consolidation and retrieval of object recognition memory. Such studies provide increasingly detailed evidence concerning both the neurotransmitter systems and the underlying intracellular mechanisms involved in recognition memory processes. They have provided evidence in support of synaptic weakening as a major synaptic plastic process within perirhinal cortex underlying object recognition memory. They have also supplied confirmatory evidence that that there is more than one synaptic plastic process involved. The demonstrated necessity to long-term recognition memory of intracellular signalling mechanisms related to synaptic modification within perirhinal cortex establishes a central role for the region in the information storage underlying such memory. Perirhinal cortex is thereby established as an information storage site rather than solely a processing station. Pharmacological studies have also supplied new evidence concerning the detailed roles of other regions, including the hippocampus and the medial prefrontal cortex in different types of recognition memory tasks that include a spatial or temporal component. In so doing, they have also further defined the contribution of perirhinal cortex to such tasks. To date it appears that the contribution of perirhinal cortex to associative and temporal order memory reflects that in simple object recognition memory, namely that perirhinal cortex provides information concerning objects and their prior occurrence (novelty/familiarity).
Highlights
Findings of pharmacological studies that have investigated the involvement of specific regions of the brain in recognition memory are reviewed
Differential Fos expression in Te2 is not dependent on the unimpaired operation of Fos-dependent consolidation processes in perirhinal cortex (Seoane et al, 2012). If these activity differences in Te2 are related to a signal that passes from perirhinal cortex to Te2 the results suggest that this signal must pass after the time that calmodulin dependent protein kinase II (CAMKII) has been activated, i.e., 420 min after acquisition (Tinsley et al, 2009, 2012), but before further processing has been disrupted by preventing Fos expression, i.e., o3 h after acquisition (Seoane et al, 2012)
Temporary inactivation of the hippocampus immediately after acquisition produced impairment in mice tested after a 24 h delay, indicating an involvement of the hippocampus in consolidation of object location recognition memory (Oliveira, Hawk, Abel, & Havekes, 2010)—interestingly, this intervention produced an enhancement of object recognition memory
Summary
Perirhinal cortex is juxtallocortex with a structure that mirrors its transitional nature between neocortex and the archicortex of the hippocampal formation (Burwell, 2001) It has neither the columns of neocortex that allow information concerning an item or feature to be concentrated in one processing module, nor the widely distributed architecture of the hippocampus that potentially allows interconnections between very many distinct items or features, but an intermediate architecture. Such an architecture presumably allows somewhat wider associations than a neocortical column but not the potentially multiple and disparate associations possible within the hippocampus (Brown, 1990). There have been other recent reviews of pharmacological studies of recognition memory (Dere, Huston, & De Souza Silva., 2007; Lyon, Saksida, & Bussey, 2011; Winters et al, 2008)
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