Single neurons in the parahippocampal region (subiculum, presubiculum, postsubiculum, parasubiculum, entorhinal cortex and perirhinal cortex) will be recorded in freely moving rats. A TV-computer based system will be developed to measure firing of a neuron as a function of head direction, place and head direction, place, and speed, turning of the head from side to side, and head elevation and pitch. The stimuli which control these spatial sensory-behavioral correlates of firing will be studied. Firing in different environments will be studied looking for constancies across environments, and ways in which these constancies can be disrupted. Electrophysiological studies of the projections of the neurons studied will be made. The slow wave theta rhythm and the relation of cell firing to the theta rhythm will be studied.