Abstract Details

Title Assessing Pupil Diameter as an Indicator of Arousal State to Distinguish Hippocampal Neural Rhythms During Wakefulness

Topic Epilepsy/Clinical Neurophysiology (EEG)

Presentation(s) P1 - Poster Session 1 (8:00 AM-9:00 AM)

Poster/Presentation
Number 6-008

Objective We determined whether pupil could serve as a reliable measure of arousal state to distinguish awake neural rhythms (e.g. hippocampal theta, gamma) from resting neural rhythms (e.g. hippocampal SPW-Rs) important for memory encoding and consolidation.

Background In rodents, hippocampal SPW-Rs (120-250 Hz) dominate offline, low-cholinergic states such as waking rest and sleep (Zhang et al. 2021) and support memory consolidation. Recent human studies discovered that hippocampal ripple-frequency events (80-120 Hz) are associated with successful memory encoding and retrieval during wakefulness (Norman 2020, Vaz 2020, Sakon 2022, Henin 2023). However, distinguishing hippocampal ripple events from high frequency gamma activity (50–90 Hz) during wakefulness remains imprecise due to artifact, coarse electrode localization, and variable detection methods (Liu, Buzsaki Nat Comm 2023). We hypothesize that combining hippocampal iEEG recordings with dynamic measurements of arousal state (cholinergic state), such as pupil diameter, could help separate gamma and ripple activity.

Design/Methods Surgical epilepsy patients at NYU Langone Health with hippocampal depth electrodes participated in a meditative color dot task simulating quiet wakefulness. Pupil data was simultaneously collected via Tobii eye-tracking systems. Putative ripples were identified in hippocampal channels showing Power Spectral Density (PSD) peaks above 60 Hz and confirmed using ripmap, a Uniform Manifold Approximation and Projection (UMAP)-based waveform clustering toolbox. Pupil diameter changes were plotted over time and split into low and high cholinergic, based on top and bottom 25% of pupil size.

Results

To date, we have enrolled 5 patients. On average, we detected 0.102 ripples per second. Pupil size time-locked to ripple peaks showed a ~50% smaller diameter compared to baseline levels measured 2 s before the ripple and to surrogate (bootstrapped) peak events.

Conclusions Preliminary evidence suggests that pupil constriction correlates with ripple peaks, in agreement with rodent data. We will continue to analyze new subjects, with a planned enrollment of 10 patients.

Authors/Disclosures
Joyce Zhu PRESENTER	Miss Zhu has nothing to disclose.
Anna Maslarova, MD, PhD	Dr. Maslarova has received research support from German Research Foundation.
Jiyun Shin, PhD	Dr. Shin has nothing to disclose.
Forouzan V. Farahani, PhD	Dr. Farahani has nothing to disclose.
Anli Liu, MD (NYU Langone Health)	Dr. Liu has received personal compensation in the range of $500-$4,999 for serving as a Consultant for ECRI. Dr. Liu has received personal compensation in the range of $500-$4,999 for serving on a Speakers Bureau for Neuropace Inc.

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