Schedule of Events | Search Abstracts | Invited Symposia | Symposia | Poster Sessions | Data Blitz

Memory reactivation during slow oscillation up-state was associated with reduced sigma-band entropy

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

Zexuan Mu¹ (), Sen Mu¹, Xiaoqing Hu¹; ¹University of Hong Kong

Targeted Memory Reactivation (TMR) during non-REM sleep strengthens memories, with efficacy critically depending on cue timing relative to slow oscillation phases. Based on the systems consolidation account, slow oscillation (SO) up states are associated with high neural plasticity and can be an optimal time window for TMR. However, empirical evidence is mixed, with neural mechanism remains unclear. We hypothesized that memory reactivation, initiated during the SO up-state, would elicit a more synchronized neural response, reflected as lower signal complexity. To test this, we pooled two overnight EEG datasets (Xia et al., 2024, N = 37; Chen et al., 2024, N = 35; total N = 72, 12,731 trials) employing similar TMR paradigms. We identified the SO phase at cue onset during N3 sleep and quantified the complexity of the subsequent time–frequency–decomposed sigma-band response (12-16 Hz) using trial-level fuzzy entropy. Linear mixed-effects modelling revealed a robust phase-dependent modulation of sigma-band entropy (FDR-corrected p_cos = .011; p_sin  = .190). Specifically, entropy was significantly lower when cues were presented during the SO up-state compared to the down-state (t(71) = –2.50, p = .015). The phase of minimal entropy occurred near the SO peak (~333°), a window known to be critical for memory consolidation. These results provide a mechanistic explanation for the time-dependency of TMR cueing: up-state cueing organizes sigma power into a more synchronous, lower-entropy pattern than the down-state. This reduced complexity may reflect more regular neural dynamics underlying memory consolidation, offering a signature of why precise cue timing is crucial.

Topic Area: LONG-TERM MEMORY: Episodic