Our mental record of past experiences is segmented into discrete episodes that are temporally structured over long time scales, and our memories for events that compose each episode are sequentially organized even further over much shorter time scales. This hierarchical organization deeply imbues our episodic memories with temporal context and supports our capacity to remember when episodes occurred in our distant past and the sequential flow of events that compose an episode. Human cognitive neuroscience has long considered episodic memories to be processed in a widely distributed network with the hippocampus serving as a fundamental hub for their formation and recall, as well as their temporal organization. In this talk, Dr. MacDonald will begin by describing his past work that identified a striking signature of temporal context in the hippocampal CA1 sub-region of awake-behaving rats wherein time cells activate in sequence to represent the flow of time within distinct episodes. Next, he will describe some of his current work that leverages genetically-defined, cell-type specificity in mice to show that CA2 – a direct input to CA1 – plays a critical role in sequentially organizing CA1 time cells and in so doing enables past events to guide a future choice. Finally, he will discuss a strategy that he has recently undertaken in order to begin to understand the circuit-level interactions between contextual memories for discrete episodes that are separated across long time scales – on the order of days. This strategy entails the use of activity-dependent and inducible genetic methods with the longer-term goal being to understand how contextual memories formed at very different points in time but with conflicting emotional content (i.e., a memory for a fearful episode vs. a memory for an extinction episode) interact to exert control over behavior. Dr. MacDonald will conclude with an overall summary of his talk and brief discussion of questions that motivate the overarching mission of my research, which is to resolve the cellular and network level principles that govern the organization of contextual memory, starting from their inception and continuing over the course of their lifetime.

To RSVP, please contact Basak Akdogan ([email protected])

This talk is part of the Cognitive & Behavioral Neuroscience Seminar series.