Why Does Brain Damage Impair Memory? A Connectionist Model of Object Recognition Memory in Perirhinal Cortex

Abstract

Object recognition is the canonical test of declarative memory, the type of memory putatively impaired after damage to the temporal lobes. Studies of object recognition memory have helped elucidate the anatomical structures involved in declarative memory, indicating a critical role for perirhinal cortex. We offer a mechanistic account of the effects of perirhinal cortex damage on object recognition memory, based on the assumption that perirhinal cortex stores representations of the conjunctions of visual features possessed by complex objects. Such representations are proposed to play an important role in memory when it is difficult to solve a task using representations of only individual visual features of stimuli, thought to be stored in regions of the ventral visual stream caudal to perirhinal cortex. The account is instantiated in a connectionist model, in which development of object representations with visual experience provides a mechanism for judgment of previous occurrence. We present simulations addressing the following empirical findings: (1) that impairments after damage to perirhinal cortex (modeled by removing the "perirhinal cortex" layer of the network) are exacerbated by lengthening the delay between presentation of to-be-remembered items and test, (2) that such impairments are also exacerbated by lengthening the list of to-be-remembered items, and (3) that impairments are revealed only when stimuli are trial unique rather than repeatedly presented. This study shows that it may be possible to account for object recognition impairments after damage to perirhinal cortex within a hierarchical, representational framework, in which complex conjunctive representations in perirhinal cortex play a critical role.

The perirhinal cortex modulates V2 activity in response to the agreement between part familiarity and configuration familiarity

“…This provides compelling evidence that MTL structures are employed in the service of perceptual tasks as well as memory tasks. These findings are also consistent with interactive models of perceptual function (Lamme and Roelfsema, 2000;Bullier, 2001;Peterson and Skow, 2008), and call for a modification to feedfowardonly models (e.g., Cowell et al, 2006;Serre et al, 2007).…”

“…If the PRC were damaged (and thus, silenced) the weights of the ''familiarity'' responses in lower-level visual cortex would be increased, allowing them to influence figure-ground assignment. This feedforward view is consistent with computational models of PRC function (e.g., Cowell et al, 2006Cowell et al, , 2010bfor review, see Cowell, 2012); to date, these models do not posit feedback to lower-level visual areas.…”

Parallel interactive retrieval of item and associative information from event memory

“…This transition from associative to item information-with a concomitant transition from slow to fast retrieval as the unitized representation can be retrieved in toto rather than constructed "on the fly"-helps explain why well-learned semantic associations are retrieved more quickly than novel event associations (Dosher, 1984;Dosher & Rosedale, 1991). Evidence for exactly this kind of representational transition has been found in the function of perirhinal cortex to encode novel unitized associations, in contrast to other regions which encode well-learned item information (Cowell et al, 2006;Haskins et al, 2008;Staresina & Davachi, 2010;Cowell et al, 2010). In addition, the kind of facilitatory interactions we found between item and associative retrieval have been implicated in the learning of whole object and category representations (Goldstone, 2000).…”

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

“…Lesions of the perirhinal cortex have been shown to impair performance on a simple visual discrimination task (Myhrer, 2000) and, more recently, the perirhinal cortex's ability to perceive and discriminate between complex stimuli seems to play a role in recognition memory (Cowell et al, 2006(Cowell et al, , 2010aMurray et al, 2007). Other research seem to confirm this hypothesis that the perirhinal cortex acts as an area where complex stimuli are processed; it has been shown to be involved in discriminating between stimuli composed of complex, overlapping components (Eacott et al, 2001) and in resolving configural feature ambiguity in object recognition memory .…”