NEURAL BASIS OF INTERNAL REPRESENTATION OF PLACE

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The study of the neural basis of spatial orientation and learning in rodents is currently providing an excellent testing ground for theories concerned both with how higher cognitive processing is carried out in the nervous system and with the biophysical dynamics of associative memory in neural networks. Neurons in the hippocampal formation appear not only to construct distributed representations of spatial location and orientation, but also to have the capability to recall these representations from memory when available sensory information is incomplete. Neurons in cortical structures intimately associated with the hippocampus appear to keep track of the animal's orientation in space independently of location, partly by making dynamic associations between visual landmarks and the integral of angular velocity information, at least some of which originates in the vestibular system. Finally, neurons in the posterior parietal cortex appear to code for the interaction between spatial location and specific movements in space in such a way as could enable the internal representation of the relationships among different parts of the environment. The studies proposed represent extensions of ongoing neurophysiological investigations in which small ensembles of single neurons are recorded from the aforementioned cortical structures during spatial behavior in rats. The principal goals are specifically to understand the neural interactions through which these high-level spatial computations are carried out, and more generally, to provide a conceptual and empirical framework for understanding the devastating consequences of damage or dysfunction in these structures in the human brain.