The overall objective of this research program is to obtain insight into the structure and function of the primate cerebral cortex. Current studies in this laboratory have focused on the connections of cytoarchitectonically defined areas of the posterior parahippocampal gyrus (PPHG) and the adjacent ventral peristriate cortices. These studies have revealed underlying principles of organization of the PPHG demonstrating that this area receives a stream of input from the visual system that is independent from the inferotemporal stream and also receives sensory input from the somatosensory and auditory association cortices. In addition important inputs arise from the multimodal areas of the superior temporal sulcus and the posterior parietal lobule as well as limbic input directly from the hippocampal formation. Behavioral data from monkeys and human stroke patients demonstrates that damage to this area produces impairments in cognitive processing and some aspects of recognition memory. Together with the anatomical data, this suggests that the PPHG functions as a nodal point for integrating highly processed cortical sensory information with the cortical output of the hippocampal formation. The specific working hypothesis is that the parahippocampal gyrus is a critical substrate for the interactions between the neocortical association areas and the medial temporal lobe limbic system that underlies normal recognition memory in monkey and man. Hence the guiding rationale for the proposed study is to establish the morphological, physiological and neurochemical substrates of information processing in the PPHG of the rhesus monkey. This hypothesis will be examined in three interrelated studies. The first study win investigate the subcortical connections of the PPHG utilizing anterograde and retrograde neuroanatomical tracers to characterize thalamic and striatal connections. This is necessary in order to evaluate the contributions of subcortical inputs and outputs to the hypothesized processing of sensory and limbic information in the PPHG. Secondly, in order to test the hypothesized interactions of sensory and limbic afferents in the PPHG we will physiologically characterize the sensory receptive field properties of neurons in this area and investigate the manner in which limbic input influences these responses. This will be accomplished by utilizing single unit recording techniques to ascertain the sensory responsivity of these neurons and the effect of limbic system stimulation on these responses. This will be followed by placing tracer injections into physiologically characterized sites to further establish the connectional basis for these physiological responses. The third study will investigate the chemical neuroanatomy underlying these physiological processes by utilizing in vitro, on-the-slide ligand binding techniques to characterize some of the major neurotransmitter afferents and their receptor subtypes that are likely to be critical to information processing and memory encoding in the PPHG. The knowledge gained from these multidisciplinary studies will enhance our understanding of the mechanisms underlying normal cortical function and the basis for disruption of cognitive processes and memory function in cases of stroke and in various types of dementia.
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