Two Halves of Theta: Representation of Current Experience and Mind-travel

Summary

Date: 
February 3, 2016 - 1:00pm
Location: 
Northwest 243
About the Speaker
Name: 
Honi Sanders (Gershman Lab)

Hippocampal place cells and entorhinal grid cells both participate in spatial representation. What is the reason for these two interacting representations of space? It had previously been thought that grid cells performed path integration as a necessary prerequisite to the identification of location expressed by place cells. However, recent results have made this understanding untenable. We propose that grid cells provide a universally applicable representation of spatial relation, which allows for simulation of as-yet unexperienced combinations of previously experienced locations. This understanding can help explain aspects of theta phase precession, which is thought to correspond to predictive simulation (mind-travel). We further propose that the two halves of the theta frequency oscillations prominent in the hippocampus are dedicated to the particular functions of place cells and grid cells in representation of current experience and mind-travel respectively. In vivo single-cell recordings from rat hippocampus support the existence of a functional differentiation between the two halves of the theta cycle: during the first half of the theta cycle rate remapping (representation of non-spatial information) is expressed, and during the second half of the theta cycle phase precession (mind-travel) is expressed.