SUBICULAR CELLS GENERATE SIMILAR SPATIAL FIRING PATTERNS IN 2 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 relate d to the spatial location of a freely moving rat as it navigates in an environment. Since the subiculum receives a strong anatomical project ion from the hippocampus, it seems possible that the subicular cell sp atial patterns are simply driven by the spatial signals from hippocamp al place cells. Data presented here, however, suggest that the two are as code space in fundamentally different ways. Here, spatial firing pa tterns of individual hippocampal and subicular cells were studied as r ats navigated in two different environments. The two chambers were a c ylinder and a square, of equal area. For some rats the two chambers we re painted to have similar visual stimulus characteristics, while for others, the two were very different. The subicular cells showed very s imilar firing patterns in the two chambers, regardless of whether they were visually similar or different. In contrast, as predicted based o n the findings of earlier studies, hippocampal place cells showed diff erent patterns in the two (again, regardless of their visual similarit y). These results suggest that the subicular cells have the ability to transfer a single, abstract spatial representation from one environme nt 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 differ ent locations in an environment. It seems possible that this represent ation may contribute to some navigational abilities exhibited by anima ls, such as dead reckoning, and novel route generation in unfamiliar e nvironments. In contrast, it appears that hippocampal place cells prov ide a spatial representation which is unique for each environment and which is strongly influenced by the exact details and overall context of the situation.