Subicular cells generate similar spatial firing patterns in two geometrically and visually distinctive environments: Comparison with hippocampal place cells

Cells in both the hippocampus and the subiculum show location related firing patterns, so that the momentary firing rate of a cell is related to the spatial location of a freely moving rat as it navigates in an environment. Since the subiculum receives a strong anatomical projection from the hippocampus, it seems possible that the subicular cell spatial patterns are simply driven by the spatial signals from hippocampal place cells. Data presented here, however, suggest that the two areas code space in fundamentally different ways. Here, spatial firing patterns of individual hippocampal and subicular cells were studied as rats navigated in two different environments. The two chambers were a cylinder and a square, of equal area. For some rats the two chambers were painted to have similar visual stimulus characteristics, while for others, the two were very different. The subicular cells showed very similar firing patterns in the two chambers, regardless of whether they were visually similar or different. In contrast, as predicted based on the findings of earlier studies, hippocampal place cells showed different patterns in the two (again, regardless of their visual similarity). These results suggest that the subicular cells have the ability to transfer a single, abstract spatial representation from one environment to another. This pattern is stretched to fit within the boundaries of the current environment. Thus, the subicular cells seem to provide a generic representation of the geometric relationships between different locations in an environment. It seems possible that this representation may contribute to some navigational abilities exhibited by animals, such as dead reckoning, and novel route generation in unfamiliar environments. In contrast, it appears that hippocampal place cells provide a spatial representation which is unique for each environment and which is strongly influenced by the exact details and overall context of the situation.