Poster A67, Saturday, March 24, 1:30–3:30 pm, Exhibit Hall C
Reinstatement of spatial information in a hybrid spatial-episodic memory task
Nora A Herweg1, Ashwini D Sharan2, Michael R Sperling2, Armin Brandt3, Andreas Schulze-Bonhage3, Michael J Kahana1; 1University of Pennsylvania, 2Thomas Jefferson University Hospital, 3University Medical Center Freiburg
The context in which we experience events helps to organize them in memory. To investigate the influence of spatial context on the organization of episodic memories, we recorded intracranial EEG data in 23 patients with medication-resistant epilepsy while they performed a hybrid spatial-free recall task. Patients navigated through a virtual town and items were presented at a sequence of locations. We relate neural similarity between encoding and retrieval events (i.e. correlation of time-frequency spectra) to the spatial contexts associated with those events. Prior research has shown reinstatement effects in the hippocampus and several cortical brain regions, but few studies have addressed the relative timing of these effects. Here, we examined the time course of reinstatement in the hippocampus and the parahippocampal gyrus, regions which have been linked to both, spatial processing and the retrieval of contextual information. We observed distinct temporal profiles of spatial context reinstatement: slopes were more positive in the parahippocampal gyrus than the hippocampus (p = 0.051). Qualitatively, spatial information (i.e. neural similarity as a function of spatial proximity) decreased in the hippocampus and increased in the parahippocampal gyrus leading up to recall. In the same time window, we observed significantly greater than chance theta phase to gamma amplitude coupling between the two regions (p < 0.05), revealing a physiologically plausible mechanism for information transfer. These results confirm the role of the MTL in retrieval of contextual information and, more specifically, contribute to our understanding of the interplay of its sub-regions during retrieval of spatial information.
Topic Area: LONG-TERM MEMORY: Episodic