Theta phase synchrony underlies successful memory retrieval

Poster Session E - Monday, April 15, 2024, 2:30 – 4:30 pm EDT, Sheraton Hall ABC

Aditya Rao¹ (amrao@sas.upenn.edu), Michael Kahana¹; ¹University of Pennsylvania

Previous studies have found that theta synchrony throughout the brain underlies improved encoding of list items. However, the details, especially the topography, of the theta synchrony effect underlying memory retrieval is poorly understood. Here, we analyzed free recall data from 375 patients implanted with intracranial electrodes for epilepsy monitoring. Each session consisted of sequentially presented word lists that the subject subsequently attempted to recall. For each macroelectrode pair, we compute the difference between theta (3–8 Hz) phase locking during the period preceding correct recall of an item, and phase locking before a matched period of silence, to generate a theta synchrony network map specific to memory retrieval function. Likewise, we examine the periods after successful versus unsuccessful word encoding and before fast versus slow recall of arithmetic facts for a comprehensive picture of memory function. We report a significant whole-brain theta synchrony effect in verbal encoding, verbal recall, and math recall. We find 44 regions in the verbal recall contrast and 20 regions in the math recall contrast that serve as significant network hubs, while no region was a significant desynchronizing hub. Among the most significant hubs were regions functionally implicated in memory function, such as the LTC, EC, and HPC, but overall, the hubs were distributed throughout the brain, especially in the case of math recall. In retrieval, we also find a positive correlation between node strength and theta power effect of memory. Future work will probe further the relationship between the functional networks of memory encoding and retrieval.

Topic Area: LONG-TERM MEMORY: Episodic