Implications of animal object memory research for human amnesia

Damage to structures in the human medial temporal lobe causes severe memory impairment. Animal object recognition tests gained prominence from attempts to model 'global' human medial temporal lobe amnesia, such as that observed in patient HM. These tasks, such as delayed nonmatching-to-sample and spontaneous object recognition, for assessing object memory in non-human primates and rodents have proved invaluable as animal models of specific aspects of human declarative memory processes. This paper reviews research in non-human primates and rats using object recognition memory tasks to assess the neurobiological bases of amnesia. A survey of this research reveals several important implications for our understanding of the anatomical basis of memory and the medial temporal lobe amnesic syndrome. First, research with monkeys and rats reveals that the contributions of medial temporal lobe structures such as the hippocampus and perirhinal cortex to memory processes are dissociable, with particular structures contributing to specific tasks on the basis of the specific type of information that a structure is optimized to process. Second, the literature suggests that cognitive tasks requiring integration of different types of information, such as in the case of complex, multimodal declarative memory, will recruit structures of the medial temporal lobe in an interactive manner. The heterogeneity of function within the medial temporal lobe, as well as the multimodal and complex nature of human declarative memory, implies that animal tests of object recognition memory, once believed to be comprehensive models for the study of human global amnesia, model just one important facet of human declarative memory. Finally, in light of the research reviewed here, it is apparent that the specific nature of amnesia observed in an individual with medial temporal lobe damage will depend on the particular medial temporal lobe regions affected and their specific representational capacities.