Subicular place cells generate the same “map” for different environments: Comparison with hippocampal cells

Since the initial discovery of place cells in the hippocampus proper, similar spatial firing has been observed in additional regions throughout the hippocampal formation. One such region is the subiculum. Here, most cells show a significant, consistent variation in rate relative to location. Thus, subicular and hippocampal cells are similar, in providing a representation of momentary location in space.However, there are also some fundamental differences. First, many subicular cells have a directional signal superimposed on the place-related patterns. In contrast, hippocampal cells in the open field paradigm used here typically do not show a genuine directional component.The second critical difference has to do with how the cells code different environments. As is well known, hippocampal cells show different spatial patterns in environments which offer distinctly different stimulus properties. For example, a hippocampal cell which fires in the northwest portion of a striped cylinder will likely display a different field, or no field, when recorded in a gray square. In contrast, subicular cells are likely to show the same behavior across environments, such as choosing the northwest region of both enclosures. Further, if two environments differ in size, the subicular patterns will expand/shrink to fit.Thus, it appears that subicular cells form a rigid framework of interrelated firing fields which is fit into each new enclosure. In contrast, hippocampal cells create a new “map” specific to each environment. This suggests that the hippocampal and subicular regions work together to help provide the overall cognitive mapping abilities of the animal.