Path integration deficits during linear locomotion after human medial temporal lobectomy.

Animal navigation studies have implicated structures in and around the hippocampal formation as crucial in performing path integration (a method of determining one's position by monitoring internally generated self-motion signals). Less is known about the role of these structures for human path integration. We tested path integration in patients who had undergone left or right medial temporal lobectomy as therapy for epilepsy. This procedure removed approximately 50% of the anterior portion of the hippocampus, as well as the amygdala and lateral temporal lobe. Participants attempted to walk without vision to a previously viewed target 2-6 m distant. Patients with right, but not left, hemisphere lesions exhibited both a decrease in the consistency of path integration and a systematic underregistration of linear displacement (and/or velocity) during walking. Moreover, the deficits were observable even when there were virtually no angular acceleration vestibular signals. The results suggest that structures in the medial temporal lobe participate in human path integration when individuals walk along linear paths and that this is so to a greater extent in right hemisphere structures than left. This information is relevant for future research investigating the neural substrates of navigation, not only in humans (e.g., functional neuroimaging and neuropsychological studies), but also in rodents and other animals.