Elisabeth A. Murray, Ph.D.

Memory loss typically accompanies strokes of the anterior communicating artery, viral infections of the brain, normal aging, and is a central feature of certain diseases such as Alzheimer's disease and AIDs dementia complex as well. To understand the mechanisms underlying storage of information in the brain we examine the effects of selective cerebral ablations and disconnections on different types of memory in macaque monkeys.

The storage of stimulus memories in monkeys is achieved in large part by a strip of cortex lying in the ventromedial aspect of the temporal lobes. This region is comprised of the entorhinal and perirhinal cortex. The perirhinal cortex, in particular, appears to be critical for accurate stimulus recognition and stimulus-stimulus association. Further, the perirhinal cortex receives information from several modality-specific neocortical regions, after processing through a series of cortical fields, and mediates stimulus recognition memory in at least the visual and somatic sensory (tactual) modalities. This same region seems to be responsible for stimulus-stimulus associative memories both within sensory modalities (i.e. intramodal associations) and across sensory modalities (i.e. crossmodal associations). Moreover, the perirhinal cortex can mediate stimulus recognition and association memory in the absence of the medial temporal lobe limbic structures, the amygdala and hippocampus. It is proposed that the perirhinal cortex is a kernel of a memory system specialized for storing knowledge about objects, analogous to a semantic memory system in humans.

Evidence from our own and other labs suggests that the perirhinal cortex is critical for "object identification". It is likely that such identification is achieved in two main ways: 1) by virtue of the information processing capability of perirhinal cortex, which resembles that of the remainder of the inferior temporal cortex; and 2) by virtue of its pivotal anatomical position, which allows the linking of representations stored in diverse sensory and motor areas.