Encoding and recall of memory for reward location in the mouse hippocampus

Abstract

The memory of where to find food can be crucial for an animal’s survival. Encoding and recall of these spatial memories involves the hippocampus, but whether and how hippocampal activity integrates memories of spatial relationships and locations is poorly understood. This thesis investigates how hippocampal activity facilitates the encoding of reward memories and how this encoding shapes hippocampal activity during memory recall in mice learning reward locations.

Encoding of memory happens in stages that depend on the hippocampal state. The thesis interrogated how two different hippocampal states, one during movement and the other during reward consumption, are affected by acetylcholine – a neuromodulator released predominantly during movement and exploration. The findings highlight how acetylcholine modulates hippocampal state and how, when experimentally altered, it can impede memory encoding.

Hippocampal activity facilitates navigation towards the learned reward locations. Individual neurons fire at specific locations of the environment, and, collectively, they cover the environment forming its cognitive map. To answer how the hippocampal activity could encode a memory of reward location, the thesis investigated how these spatial representations and the population activity change after learning. I found that the reward memory shapes the activity in the dorsal CA1 of the hippocampus by modulating its overall population activity and in the intermediate CA1 by modulating the activity of a reward-specific cell population.

Together, these results suggest how hippocampal activity could facilitate encoding and recall of memory for reward locations.