Poster D69, Monday, March 26, 8:00-10:00 am, Exhibit Hall C
Functional wiring of the human medial temporal lobe
Ethan Solomon1, Joel Stein1, Sandy Das1, Michael Sperling2, Kareem Zaghloul3, Cory Inman4, Bradley Lega5, Kathryn Davis1, Gregory Worrell6, Barbara Jobst7, Daniel Rizzuto1, Michael Kahana1; 1University of Pennsylvania, 2Thomas Jefferson University Hospital, 3National Institutes of Health, 4Emory School of Medicine, 5University of Texas Southwestern, 6Mayo Clinic, 7Dartmouth Medical Center
Storing episodic memory is an inherently integrative operation, long conceptualized as a process that binds information about new experiences to a prevailing neural context. Neural synchronization, or the correlated spectral activity between different parts of the brain, has been proposed as a general mechanism for this binding process. However, the dynamics of neural synchronization in the human brain are largely unexplored, especially at the fine spatial scales of critical memory areas like the medial temporal lobe (MTL). Here, we characterize synchronization within substructures of human MTL that occurs during verbal memory encoding and retrieval. We leverage a large dataset of 87 subjects fitted with indwelling electrodes in the MTL and use connectivity measures which are resistant to electrical artifacts (the weighted phase-lag index). We find that, during successful encoding, MTL substructures tend to synchronize at low frequencies (theta/apha, 4-13 Hz). Particularly strong coupling was observed between the rhinal and parahippocampal cortices (PHC), but connections were also found between CA1, subiculum, and rhinal cortex. At higher frequencies (gamma, 30-90Hz), we observe strong desynchronizations of neural activity but note that synchronization is observed if volume-conduction artifacts are not considered, refuting longstanding notions of intra-MTL gamma synchronization. Moreover, we observe elevated spectral power in the gamma band during periods of enhanced theta/alpha synchronicity. Taken together, our results (1) highlight the PHC-rhinal junction as a locus of synchronous theta/alpha activity during memory formation, and (2) de-emphasize the importance of inter-regional gamma synchronization as a substrate of human memory.
Topic Area: LONG-TERM MEMORY: Episodic