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Network Activation During Sleep Slow Oscillations Differs Based on Their Coupling with Spindles.

Poster Session C - Sunday, March 8, 2026, 5:00 – 7:00 pm PDT, Fairview/Kitsilano Ballroom

Sounak Dey^1,2 (), Sara Mednick³, Paola Malerba^2,4; ¹Carle Illinois College of Medicine, ²The Research Institute at Nationwide Children’s Hospital, ³University of California Irvine, ⁴The Ohio State University School of Medicine

Sleep slow oscillations (SOs, 0.5-1.5 Hz) support functions such as synaptic homeostasis, glymphatic clearance and memory consolidation. Complexes of one SO followed by a spindle within a short delay are causally linked to overnight episodic memory consolidation, yet little is known about region-specific activation during SO-spindle complexes versus uncoupled SOs. As these complexes may support neuronal engram reactivation required for consolidation, understanding their selective network involvement is crucial. We compared the current source density (CSD) of cortical and subcortical regions during spindle-coupled and uncoupled SOs in the nighttime sleep high-density EEG of 22 participants. Each SO CSD was encoded as a region-by-time matrix, with entries serving as features. Functional connectivity (FC) between features was measured using mutual information. We compared FC under three conditions: within each SO, between subsequent SOs, and in subnetworks of interest (thalamo-hippocampal-cortex (HTC), basal ganglia, and mesolimbic-with-brainstem). Analyses were conducted separately for N2 and N3 sleep. Within-SO analyses revealed that coupled SOs exhibited higher overall FC and significantly more high-FC feature pairs than uncoupled events. FC between subsequent SOs was not sensitive to inter-event delay. Subnetwork analyses showed strong FC differences in HTC for coupled versus uncoupled SOs in both N2 and N3, with additional basal ganglia differentiation in N2. Our study introduces a strategy for exploring CSD-based FC in sleep EEG events and demonstrates its utility in identifying coupling-related network engagement. Findings suggest enhanced HTC and basal ganglia FC during coupled SOs, with greater coupling-related differentiation in spindle-rich N2 compared to SO-rich N3 sleep.

Topic Area: LONG-TERM MEMORY: Episodic