Neurons in the rat hippocampal formation play an important role in spatial information encoding. The neurons in the different regions of this medial temporal lobe structure have different spatial and temporal firing properties, suggesting differences in the way information is processed through the regions. The specific aims of this project are to: 1) develop accurate statistical models of single neurons in CA3, the subiculum, and the entorhinal cortex that describe the relationship between neural spiking activity and relevant covariates such as the position of the animal in its environment, theta phase, theta phase precession, bursting, running velocity and the spiking history of other neurons; 2) develop accurate statistical models that describe the joint spiking activity of sets of neurons in order to measure coordinated spiking activity patterns across an ensemble of simultaneously recorded neurons within the same region or a different region; 3) test the hypothesis that the effects of behavioral correlates on single neuron activity in CA3, CA1, subiculum and the deep entorhinal cortex differ according to whether the animal is performing a task that either does or does not depend on an intact hippocampus; and 4) test the hypothesis that patterns of coordinated multiple neuron activity in CA3, CA1, the subiculum and the deep entorhinal cortex differ according to whether the animal is performing a task that either does or does not depend on an intact hippocampus. These differences in coordinated activity may offer insight into how the rat hippocampus maintains representations of relevant spatial information and facilitates transfer of that information to other brain regions. The experimental methods will include use of multielectrode arrays to record simultaneously the activity of neurons in the hippocampal formation, as well as application of point process theory to develop accurate statistical methods to characterize the firing properties of hippocampal ensembles and their relation to behavioral and neurophysiological covariates. The broad long-term objectives are to: develop a statistical paradigm tailormade for the analysis of spike trains from multiple electrode recordings; and characterize how ensemble neuronal activity in the hippocampal formation represents information in short-term memory and how it aids in encoding and retrieval of information from long-term memory. The potential health benefits of the experimental research are a better understanding of the basic neurophysiology of hippocampal dependent memory processes and insight into how to develop new treatments for memory dysfunction. More accurate characterizations of neuronal dynamics may also lead to more physiologically-sound approaches to creating machine-brain interfaces and designing neural prosthetic devices.