Sleep spindles are thalamocortical oscillations that contribute to sleep maintenance
and sleep-related brain plasticity. The current study is an explorative study of the
circadian dynamics of sleep spindles in relation to a polygenic score (PGS) for circadian
preference towards morningness. The participants represent the 17-year follow-up of
a birth cohort having both genome-wide data and an ambulatory sleep electroencephalography
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 PGS for circadian preference
towards morningness across the whole genome, including 354 single-nucleotide polymorphisms.
Stage 2 slow (9-12.5 Hz, N = 186 739) and fast (12.5-16 Hz, N = 135 504) sleep spindles
were detected using an automated algorithm with individual time tags and amplitudes
for each spindle. There was a significant interaction of PGS for morningness and timing
of sleep spindles across the night. These growth curve models showed a curvilinear
trajectory of spindle amplitudes: those with a higher PGS for morningness showed higher
slow spindle amplitudes in frontal derivations, and a faster dissipation of spindle
amplitude in central derivations. Overall, the findings provide new evidence on how
individual sleep spindle trajectories are influenced by genetic factors associated
with circadian type. The finding may lead to new hypotheses on the associations previously
observed between circadian types, psychiatric problems and spindle activity.
