TY - JOUR T1 - Episodic memory formation in naturalistic viewing JF - bioRxiv DO - 10.1101/2022.05.24.485821 SP - 2022.05.24.485821 AU - Andrey R. Nikolaev AU - Inês Bramão AU - Roger Johansson AU - Mikael Johansson Y1 - 2022/01/01 UR - http://biorxiv.org/content/early/2022/06/23/2022.05.24.485821.abstract N2 - The brain systems of episodic memory and oculomotor control are tightly linked, suggesting a crucial role of eye movements in memory. But little is known about the neural mechanisms of memory formation across eye movements in naturalistic viewing behavior. Here, we leverage simultaneous recording and analysis of eye movements and EEG to examine the formation of episodic memory in free viewing. Participants memorized multi-element events while their EEG and eye movements were concurrently recorded. Each event comprised elements from three categories (face, object, place), with two exemplars from each category, in different locations on the screen. A subsequent associative memory test assessed participants’ memory for the between-category associations that specified each event. We overcame the problem of overlapping EEG responses to sequential saccades in free viewing using a deconvolution approach. Brain activity was segmented relative to the fixation onsets and we examined EEG power in the theta and alpha frequency bands, the putative oscillatory correlates of episodic encoding mechanisms. High subsequent memory performance was predicted by three modulations of fixation-related EEG during the event memory formation: 1) theta synchronization at fixations after between-category gaze transitions, 2) theta synchronization at fixations after within-element gaze transitions, 3) alpha desynchronization at fixations after between-exemplar gaze transitions. Thus, event encoding with unrestricted viewing behavior was characterized by three neural mechanisms, manifested in fixation-locked theta and alpha EEG activity that rapidly turned on and off during the unfolding eye movement sequences. These three distinct neural mechanisms may be the essential building blocks that subserve the buildup of coherent episodic memories during naturalistic viewing behavior.Competing Interest StatementThe authors have declared no competing interest. ER -