Active spatial information processing in the septo-hippocampal system

The hippocampal formation (HF) receives the final outputs from all association cortices, and processes and integrates this diverse information. Our neurophysiological data in rats and monkeys suggest active selection of relevant sensory information in the HF. In an open field, rat HF neurons strengthened their sensitivity to more relevant variables among various movement variables such as movement speed, direction, and turning angle based on navigation contexts. The HF place-related activity in the monkey, which rode on a movable cab, became obscure in passive translocation of a monkey by an experimenter. This suggests that the animal actively senses the environment surrounding it during spatial navigation, and that spatial correlates of HF neurons depend on this active sensing. In the monkey septal nuclei that receive hippocampal outputs, some neurons were differential to specific views from 4 specific locations in an experimental room (place-differential responses). Multidimensional scaling (MDS) analysis of place-differential responses indicated that the 4 locations represented in a 2-dimensional virtual space at relative positions were similar to those in the real experimental room. This might be a neurophysiological basis of a cognitive map and path finding. These results are consistent with recent human PET studies that indicated HF involvement in recalling routes and landmarks. Thus, a cognitive mapping system represented in the HF plays a pivotal role in active computation for path finding.