Freyja OLAFSDOTTIR

The Role of Hippocampal Replay in Memory and Planning

Lab: University College London (GB)

Abstract: The hippocampus is important for spatial and episodic memory. Place cells – the principal cell of the hippocampus, represent information about an animal’s spatial location. Yet, during rest and awake quiescence place cells spontaneously recapitulate past trajectories (‘replay’). Replay has been hypothesised to serve a variety of functions, such as spatial planning and systems consolidation – the stabilisation of a new memory trace, likely through the maturation of a complementary cortical memory. In my talk I will describe recent work I have carried out which shows replay may indeed support both planning and consolidation. In past work, we found during rest periods place and grid cells, from the deep medial entorhinal cortex (dMEC, the principal cortical output region of the hippocampus), replayed coherently. Importantly, dMEC grid cells lagged place cells by ~11ms; suggesting the replay coordination may reflect consolidation. Moreover, we found replay occurring just before movement to or upon arrival at a reward site preferentially depicted locations and trajectories consistent with the animals’ current task demands; perhaps indicative of spatial planning. If animals lingered at reward sites, however, no biases in replay content were observed. Importantly, the occurrence of task-focused replay predicted accurate spatial decisions. Thus, replay may abruptly yet flexibly switch between a planning and consolidation function in response to task demands. Finally, I will discuss some unpublished data investigating how dMEC-hippocampal coordination changes as a function of experience with a spatial task and how these changes may underpin learning.

Inmed meeting room, Monday October 1st, 11 a.m.