By Sam Gershman

The hippocampus contains “place cells” that fire when an animal occupies a specific part of space. This observation inspired the idea that the hippocampus represents a “cognitive map” of space. Evidence suggests that the hippocampal cognitive map is really a mosaic of maps for particular contexts; place cells remap whenever there is a change in context. This raises the question of how the hippocampus knows when the context has changed, and how it discovers new contexts. This paper proposes that contexts correspond to hidden states of the environment, and that place cells track beliefs about the hidden state, such that remapping occurs when these beliefs change. This theory can explain not only when remapping occurs, but also why place cells frequently remap only partially. According to the hidden state theory, beliefs are probabilistic and hence remapping is inherently graded. This theory takes a step towards reconciling the puzzling variety of remapping phenomena. It also generates new experimental predictions: we are currently looking at how changes in an animal’s uncertainty about hidden states affects remapping.

Sam Gershman is an Associate Professor of Psychology at Harvard University.

Learn more in the original research article:

Hippocampal remapping as hidden state inference. Honi Sanders, Matthew A Wilson, Samuel J Gershman. eLife 2020; 9:e51140.