Spatial Reference Memory is Associated with Modulation of Theta-Gamma Coupling in the Dentate Gyrus.

Spatial reference memory in rodents represents a unique opportunity to study brain mechanisms responsible for encoding, storage and retrieval of a memory. Even though its reliance on hippocampal networks has long been established, the precise computations performed by different hippocampal subfields during spatial learning are still not clear. To study the evolution of electrophysiological activity in the CA1-dentate gyrus axis of the dorsal hippocampus over an iterative spatial learning paradigm, we recorded local field potentials in behaving mice using a newly designed appetitive version of the Barnes maze. We first showed that theta and gamma oscillations as well as theta-gamma coupling are differentially modulated in particular hippocampal subfields during the task. In addition, we show that dentate gyrus networks, but not CA1 networks, exhibit a transient learning-dependent increase in theta-gamma coupling specifically at the vicinity of the target area in the maze. In contrast to previous immediate early-gene studies, our results point to a long-lasting involvement of dentate networks in navigational memory in the Barnes maze. Based on these findings, we propose that theta-gamma coupling might represent a mechanism by which hippocampal areas compute relevant information.