The Roles of Grid and Place Cells and Phase Precession in Human Episodic Memory

This research project uses direct human brain recordings to characterize the neuronal signals that represent aspects of individual episodic memories. A key question is understanding how the brain supports tasks such as “Where did I leave my keys this morning?” We will test the hypothesis that “grid cells” in the human entorhinal cortex provide a coordinate system that represents the spatial information that is stored in individual episodic memory traces. We perform this work by examining direct brain recordings from epilepsy patients who have electrodes implanted to map their seizure outcomes. During recordings patients will perform a novel hybrid spatial-episodic memory task in which they navigate a virtual environment and encounter different objects throughout the environment. Because object encounters act as episodic memories, we will probe the neural basis of episodic memory representation by asking them to remember these events while we measure the activity of their grid and place cells. Our main hypothesis is that the activity of grid cells during memory retrieval represents the spatial location where the event occurred. We also test the role of grid cells in memory retrievals based on cues as well as self-initiated recalls from memory search. We will also test our novel hypotheses that the temporal order of memories is represented computationally by the brain via theta-band phase coding.