Characterizing hippocampal activation with magnetoencephalography using the Mnemonic Similarity Task

1081 

Abstract Submission 

Pei Robins¹, Jessica Gilbert², Zhi-De Deng¹

¹National Institutes of Health, Bethesda, MD, ²NIMH/NIH, Bethesda, MD

Pei Robins  
National Institutes of Health
Bethesda, MD

Jessica Gilbert  
NIMH/NIH
Bethesda, MD

Zhi-De Deng, PhD  
National Institutes of Health
Bethesda, MD

The hippocampus is crucial for memory formation and consolidation, and aspects of emotion regulation in psychiatric disorders such as depression. The Mnemonic Similarity Task (MST) is a pattern separation task that can be used to measure hippocampal function. This study aims to determine the feasibility of magnetoencephalography (MEG) to characterize hippocampal activation during the MST in a cohort of healthy participants.

Sixteen healthy participants completed the MST, comprising of two phases. In the encoding phase, 120 pictures of everyday objects were presented. In the retrieval phase, 360 pictures comprised of 120 each of repeated, new, and similar pictures were presented, and participants were asked to categorize them. Pattern separation performance was measured by the Lure Discrimination Index (LDI) and Recognition (REC) score. MEG data was recorded on a 275-channels CTF system. The data was filtered and artifacted using Independent Component Analysis (ICA) to remove cardiac, blinking, and movement artifacts. Source reconstruction was performed using the linearly constrained minimum variance beamformer method.

The mean LDI was 0.35±0.20. The mean REC was 0.61±0.12. Participants were significantly faster in recognizing old objects compared to identifying similar objects (t=-5.6, p<.001). MEG revealed peak hippocampal activation approximately 200ms post-stimulus onset during both encoding and retrieval phases. The peak activation is observed in anterior hippocampus.

Our results demonstrate that MEG during the pattern separation task can detect hippocampal activation during the memory encoding and retrieval phases. Future directions include using this task to assess hippocampal function in depressed patients receiving electroconvulsive therapy.

Long-Term Memory (Episodic and Semantic) ¹

EEG/MEG Modeling and Analysis ²

MEG

Memory

Sub-Cortical