This project investigates a key issue in human navigation. How does the medial temporal lobe (MTL) process information about space, time, and self-motion to keep us oriented while walking about? Extensive experimentation in rodents indicates that brain structures in the MTL play an important role in navigation, but currently there is a pressing need to validate the relevance of animal studies for understanding human navigation. In addition, there is very little data concerning the effects of brain injury on navigation ability, particularly within the nearby environment. The work in this project will bridge this gap by testing the navigational abilities of patients who have had part of the MTL removed as therapy for severe epilepsy. The project will answer the following questions: (1) Are deficits in navigation after MTL surgery due specifically to removal of MTL tissue, or instead to other factors related to the disease necessitating the surgery? (2) What specifically are the consequences of MTL injury for navigation? (3) How specialized are MTL structures for navigation? (Are only some types of navigation impaired but not others?) (4) Does the right hemisphere MTL play a more dominant role than the left for human navigation? The proposed experiments will provide a firm empirical foundation for understanding the effect of brain injuries and psychiatric disorders that impact the MTL. The work focuses specifically on navigation ability and will be particularly relevant for evaluating the homology of brain structures that subserve navigation in animals and humans. The studies are unique in that they will test a rare population of neurosurgical patients, using methods that focus on the perception of self-motion at an unprecedented level of detail. Furthermore, the methodology will allow an assessment of the possible non-specific effects on navigation of epilepsy and epilepsy medication. This basic data will be highly valuable for interpreting future research involving similar patients. [unreadable] [unreadable]