Dorsal CA1 Hippocampal Place Cells Form a Multi-Scale Representation of Megaspace

Abstract

Spatially firing "place cells" within the hippocampal CA1 region form internal maps of the environment necessary for navigation and memory. In rodents, these neurons have been almost exclusively studied in small environments (<4 m2). It remains unclear how place cells encode a very large open 2D environment, which is more analogous to the natural environments experienced by rodents and other mammals. Such an ethologically realistic environment would require a more complex spatial representation, capable of simultaneously representing space at overlapping multiple fine to coarse informational scales. Here we show that in a megaspace (18.6 m2), the majority of dorsal CA1 place cells exhibited multiple place subfields of different sizes, akin to those observed along the septo-temporal axis. Furthermore, the total area covered by the subfields of each cell was not correlated with the number of subfields, and this total area increased with the scale of the environment. The multiple different-sized subfields exhibited by place cells in the megaspace suggest that the ensemble population of subfields form a multi-scale representation of space within the dorsal hippocampus. Our findings point to a new dorsal hippocampus ensemble coding scheme that simultaneously supports navigational processes at both fine- and coarse-grained resolutions.