COMPUTATIONAL ASPECTS OF PRIMATE MEMORY

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Active short-term memory plays a critical role in the temporal organization of behavior, reasoning, and language. It is impaired in a variety of mental disorders, notably in the psychoses, major affective disorders and syndromes resulting from pathological aging of the brain. Recent experimental evidence indicates that active short-term memory consists in the sustained activation of an extensive network of interconnected neuronal assemblies of the cerebral cortex. Memory networks are widely distributed, extending beyond the boundaries of anatomically defined cortical areas. The mechanisms of active memory are believed to include the sustained circulation of neuronal impulses within one such network. This research will attempt to substantiate the distributed nature of active short-term memory and the reentry of neural impulses presumed to be the basis of short-term memory retention. Experiments with that objective will be conducted in nonhuman primates trained to perform auditory, tactile, and cross-modal memory tasks. Fields potentials and cell discharge will be recorded from frontal and parietal regions of the cortex during performance-and also to some extent during learning-of those tasks. Frequency and pattern of cell discharge will be analyzed for evidence of neuronal interactions within and between those cortical regions during the short-term memorization of sensory information. Special computational methods of time-series analysis will be used to explore those interactions. Some of the interactions will be further explored by reversible functional depression (by local cooling) of frontal cortex and the study of its effects on parietal cell discharge and the animal's performance of haptic memory tasks. The results of these studies are expected to shed light on the functional architecture of cortical memory networks and on the mechanisms of encoding, retention, and retrieval of memory. A better understanding of the neural dynamics of memory may help us better understand the pathogenesis of memory disorders in the mentally ill and thus lead to better treatments.