Sleep regulation is closely associated to HPA activity. Alterations in both systems may be precursors of psychiatric disorders like depression even at an early stage of development. So far the impact of microstructure in sleep regulation like sleep spindles is unknown. In recent studies, sleep spindles have been linked to efficient cortical-subcortical connectivity and cognitive abilities especially during neurodevelopment.

Sleep spindles in kindergarten children were analyzed and related to sleep regulation and HPA axis functioning.

Patients and Methods: Nine five-year old kindergarten children were enrolled in a cross-sectional examination of HPA system activity assessed by saliva cortisol measurements (morning cortisol after awakening) and sleep regulation investigated by sleep EEG-monitoring. Sleep EEG spindles were visually scored and were put into relation to macrostructural sleep and HPA activity parameters.

Sleep spindles were correlated to basal morning cortisol secretion (AUC basal) (curvilinear r = .83, p = .01), though were negatively correlated to cortisol increase (AUC netto) after awakening (r = -.77, p < .05). Though not statistically significant but by trend, spindle density (i.e. number of spindles per hour of stage 2 -sleep) is negatively correlated to REM density (r = - .57, p = .11), as increase of awakening cortisol was associated to REM density by trend (r = .63, p = .07).

Not only sleep continuation parameters as reported before but also sleep microstructure reflected by sleep spindles may be associated to sleep regulation and HPA system functioning.