0073 Do Slow Wave Sub-types Serve Distinct Roles in Sleep Homeostasis and Plasticity?

Introduction Recent research distinguishes two slow wave (SW) subtypes: slower (SSW) and faster slow waves (FSW). Early research on these subtypes suggests that FSW positively correlate with sleep pressure, while SSW are associated with memory. Developmental data from children who nap provide an opportunity to test this distinction. Prediction 1: If FSW are associated with sleep pressure, we expect more FSW during overnight sleep when children do not nap compared to overnight sleep following daytime naps. Prediction 2: If SSW are associated with memory, we expect stronger and more synchronized coupling between spindles (SP) and SSW compared to FSW, reflecting memory processing. Methods This is a secondary analysis of data from 25 children (3-5 yrs). Children participated in two conditions; they either napped (NO) or stayed awake (WO) during the daytime nap interval. The nap and subsequent overnight sleep in both conditions was PSG-recorded. SWs (0.5-4 Hz) and SPs (10.3-13.3 Hz) were detected during NREM sleep in the frontal region. To distinguish between slow and fast SWs, the transition frequency from the down-to-up state of SWs was utilized. Coupling amount (strength) and direction of coupling (phase) were quantified for both SSW-SP and FSW-SP coupling. Results Prediction 1: A higher occurrence of FSW were observed during WO compared to NO (t(24)=-2.70, p=0.01). However, after adjusting for NREM sleep duration, FSW density did not differ between NO and WO (p=0.75). Prediction 2: SSW-SP coupling strength was lower compared to FSW-SP coupling strength during WO (t(24)=-2.43, p=0.02), but there were no differences in the NO condition (p=0.25). Additionally, there were no significant differences in the coupling phase between SSW-SPs and FSW-SPs in either overnight bout (p>0.45). Conclusion Increased sleep pressure (nap absence) did not directly affect FSW density. Instead, the absence of naps extended NREM sleep duration, elevating FSW occurrence. Moreover, SSW-SP coupling was weaker than FSW-SP coupling and only during WO, contrary to our prediction that SSW are associated with learning. While it is possible that SSW and FSW functionality is still developing at this age, these data fail to support predictions of the distinct role of SW subtypes. Support (if any)