10:00–11:00 am
Please Join us:
Yu Hung Chiu's PhD Thesis Defense
Monday, August 28 at 10:00 AM CDT
HIPPOCAMPAL COGNITIVE MAP DYNAMICS: INVESTIGATING THE FATE AND REPLAY OF PLACE CELLS
The hippocampus is known to play a role in encoding, consolidating, updating and retrieving episodic memories. But the mechanism underlying these processes remains unclear. My work focuses on investigating hippocampal network and cellular dynamics in subregion CA1 during and across episodes of experience, giving insight on how memories are updated and retrieved.
We first investigated the association between the spatial preciseness of place fields (PFs) and the representational drift across sessions in the same environment. We reanalyzed data from experiments in which male mice navigated familiar and novel environments for blocks of trials across days (distinct temporal episodes), and experiments in which mice changed their reward expectation across blocks of trials (distinct internal state episodes). We found that PFs that underwent a drift across episodes showed lower spatial precision in the preceding block of trials. We suggest a conceptual model explaining the association between PF precision and drift that involves changes in CA3 input to CA1 and synaptic plasticity at CA1-CA3 synapses.
We then investigated another feature in hippocampus that is closely related to memory - place cell sequence replay. We investigated how the rate and fidelity of replay events were be modulated by reward contingencies and fear memory. We observed that replay rate dropped when reward was removed from blocks of trials and increased when reward was put back for blocks of trials. We also observed that associating an environment with an aversive shock significantly modulated the rate and fidelity of replay events.
Together these results give insight into how network and single cell dynamics within the hippocampus facilitate memory formation, consolidation and retrieval of rewarding and aversive experiences.
Committee Members: Prof. Jason MacLean (Chair) Prof. Stephanie Palmer Prof. Heinrich Jaeger Prof. Mark Sheffield