Role of the Primate Perirhinal Cortex in Memory and Emotional Regulation: Ontogeny and Early Insults

The perirhinal cortex, a small strip of the anterior medial temporal cortex, first came into prominence through studies of memory. While examining patients with damage to the medial temporal lobe as well as animals with similar regional damage, findings showed that combined damage to the hippocampus, amygdala, and adjacent cortical areas, including the perirhinal cortex, were responsible for the profound memory loss observed. Later, however, the evidence demonstrated that the accompanying damage to the underlying medial temporal cortical areas were largely responsible for the memory deficit that had been attributed to the combined hippocampal and amygdala lesions. The perirhinal cortex has become appreciated as a critical structure supporting familiarity judgement, recognition memory, flexible executive control and behavioral regulation. The objective of this article is first to review the anatomy of the perirhinal cortex and its interactions with other medial temporal structures as well as the neocortex. A series of neurosurgical ablation studies in nonhuman primates will provide evidence for its role in memory and behavioral regulation in adulthood. The next section will highlight the functional maturation of the perirhinal from infancy through adulthood and will show that its role in support of recognition memory emerges in early infancy. The findings will also show that the neonatal perirhinal dysfunction results in functional compensation of recognition and working memory in adulthood but impacts higher-order executive processes such as cognitive control and flexibility. Interestingly, the discovery of the role of perirhinal cortex in familiarity judgements instead of recollection, which is mediated by the hippocampus, is now well documented in several clinical neurodevelopmental disorders (epilepsy, Alzheimer's disease, schizophrenia), providing valuable markers in the prodromal phase of the diseases for early diagnosis and treatment.