NEURAL BASIS OF INTERNAL REPRESENTATION OF PLACE

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The objective of this project is an understanding of the neural mechanism underlying the formation of internal representations of places, and the linkage of these representations in the guidance of spatial navigation. The primary hypothesis under consideration is that place learning involves the formation of an internal transition matrix which links information about a given location with movement information in order to reconstruct, by associative recall, a representation of the corresponding target location. A minimal model is presented for the neural implementation of this computational scheme, which describes how the associative property of long-term synaptic enhancement could be used to accomplish this task. There are four main parts to the proposed project. First will be an investigation of the nature of the spatial and movement representations in rat cortical areas which converge on the hippocampal formation. We will apply a novel neurophysiological technique, which permits the recording and analysis of the behavioral correlates of several single units at the same time. We will also explore further the relation of dentate gyrus neuronal activity to spatial memory and/or decision making which is suggested by the results of the previous support period. This will be carried out in two different studies which will combine single unit recording and the analysis of changes in synaptic efficacy and/or post-synaptic excitability during spatial "working" memory. Finally, we will analyze the specific role of long-term synaptic enhancement in the control of place specific neuronal discharge in the hippocampal formation of freely moving rats during a spatial memory problem. The latter study should clarify the relative importance of "hard wiring" versus modulation of synaptic gain in this process during both stimulus-driven, and memory-driven spatial orientation. The overall project is expected to provide data which will aid in the construction of a general model for the brain mechanisms underlying more complex, but analogous, types of information processing found in humans, and which are characterized by the formation of conditional associations between actions and their consequences under different contexts.