The goal of this program of research is to provide a comprehensive neuroanatomical analysis of the two major regions of the primate limbic system the hippocampal formation and the amygdaloid complex. The hippocampal formation has been implicated in the mediation of long term declarative memory and the amygdaloid complex is involved in species-specific behaviors and emotion. During the past year we have completed studies directed at determining the entire complement of cortical sensory inputs to the hippocampal formation that enter via the adjacent perirhinal and parahippocampal cortices. These studies were carried out by placing intracerebral injections of the retrograde tracers fast blue and diamidino yellow into different positions within the perirhinal and parahippocampal cortex and mapping the location of labeled neurons in other regions of the neocortical mantle. In the amygdala, we have focused on studies of its intrinsic circuitry. Analyses of the intranuclear and internuclear connections of the lateral nucleus have been completed and studies of similar connections of the basal nucleus are currently under way. We have also begun a series of studies to determine the circuitry by which the amygdala influences visceral and autonomic regions of the brain during emotional behavior. In particular, we are using the combination of retrograde neural tracing and in situ hybridization techniques to determine whether the major output pathway of the amygdala uses the inhibitory neurotransmitter gaba. Taken together, these data provide substantial insight into how temporal lobe limbic regions mediate the formation and consolidation of memory and allow the appreciation of species-specific emotional communication.
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