Polygenic impact of morningness on the overnight dynamics of sleep spindle amplitude

Sleep spindles are thalamocortical oscillations that contribute to sleep maintenanceand sleep-related brain plasticity. The current study is an explorative study of the cir-cadian dynamics of sleep spindles in relation to a polygenic score (PGS) for circadianpreference towards morningness. The participants represent the 17-year follow-upof a birth cohort having both genome-wide data and an ambulatory sleep electroen-cephalography measurement available (N= 154, Mean age = 16.9, SD = 0.1 years,57% girls). Based on a recent genome-wide association study, we calculated a PGSfor circadian preference towards morningness across the whole genome, including354 single-nucleotide polymorphisms. Stage 2 slow (9-12.5 Hz,N= 186 739) andfast (12.5-16 Hz,N= 135 504) sleep spindles were detected using an automatedalgorithm with individual time tags and amplitudes for each spindle. There was a sig-nificant interaction of PGS for morningness and timing of sleep spindles across thenight. These growth curve models showed a curvilinear trajectory of spindle ampli-tudes: those with a higher PGS for morningness showed higher slow spindle ampli-tudes in frontal derivations, and a faster dissipation of spindle amplitude in centralderivations. Overall, the findings provide new evidence on how individual sleep spin-dle trajectories are influenced by genetic factors associated with circadian type. Thefinding may lead to new hypotheses on the associations previously observedbetween circadian types, psychiatric problems and spindle activity.