Topographical relocation of sleep spindles and their relation to internalizing problems: A longitudinal approach

Introduction:
Among the most common emotional problems experienced by children and adolescents are internalising problems (IP), which are primarily inwardly directed emotional difficulties. Research has established a strong link between affective disorders and sleep problems. Specifically, lower sleep spindle activity, a hallmark of N2 sleep, has been connected to IP in children and adolescents. However, most studies have focused on examining this relationship at a single point in time, hampering our understanding of how developmental changes in sleep parameters and IP are related. Here, we investigated the topographical developmental trajectories of sleep spindles and tested, whether deviations from these patterns predict IP.
Method:
We conducted polysomnographic recordings and measured IP via questionnaires across 15 years in a sample of subjects (N =28, 19 female) at three time points: (1) childhood (~9.5yrs), (2) adolescence (~16yrs), and (3) young adulthood (~22.5yrs). Two nights were recorded at each time point (adaptation and experimental night). To assess the topographical spindle pattern, we measured slow (11-13Hz) and fast (13-15Hz) spindle densities (N/min) during N2 sleep.
Results:
Associations with internalising problems were found specifically in the frontal region in relation to deviations from typical slow spindle density development. Frontal slow spindle density remained stable between childhood and adolescence (t(27) = 0.65, p = .677, MD = 0.19). A stronger individual decrease in frontal slow spindle density during this period was associated with higher IP scores in adulthood (rsp = - .44, p = .018). Conversely, slow spindle density typically decreased from adolescence to adulthood (t(27) = 7.88, p < .001, MD = 1.57). During this period, a greater decline predicted lower levels of IP in adulthood (rsp = .44, p = .020).
Conclusion:
The results of this study provide evidence that frontal slow spindle development is associated with IP during adulthood. We found this association to be dynamic, with the direction of the effect being dependent on the developmental period. A timely decrease in slow spindle density from adolescence to adulthood might indicate healthy maturation of frontal networks which are implicated in internalisation, whereas a premature decrease of slow spindle density during puberty might hint at compromised brain development.