Local Differences in Computational Sleep Depth Parameters in Healthy School-aged Children.

Objective. Slow wave sleep in children reflects several processes, such as sleep pressure, synaptic density, and cortical maturation. Deep sleep in children is abundant and our aim was to discover whether examining electroencephalography (EEG) mean frequency would help separate these processes. Methods. Sleep EEG of 28 generally healthy 7- to 11-year-old children (14 first graders, 14 third graders, 14 girls, 14 boys) was analyzed. Median non-rapid eye movement (NREM) sleep EEG frequency (median sleep depth, in Hz) and the amount of computational deep sleep using the thresholds of 2 Hz and 4 Hz (DS2% and DS4%, respectively) were calculated from the frontopolar, central, and occipital EEG derivations. Results. Median NREM sleep frequency was lower in the left frontopolar area than more posteriorly in the whole study group, in the third graders and in the girls. In the left hemisphere, the amount of DS4% was higher frontopolarly than occipitally in the third graders and in the girls. The amount of DS2% was higher frontopolarly than centrally in all groups except in the first graders. In the whole study group, DS4% declined smoothly across the NREM episodes, whereas DS2% centered in the first NREM sleep episode. Discussion. The median NREM sleep EEG frequency results might denote earlier frontal maturation in girls than in boys. Interestingly, we found frontopolar predominance in slow mean EEG frequency in both hemispheres, even if frontal slow wave activity is found to enhance until adolescence. As with infants, it seems that slower sleep EEG frequencies do not reflect sleep pressure as well as <4 Hz activity in school-aged children either. Conclusion. Our analysis method suggests that in addition to slow wave activity, EEG frequency analysis might be useful in differentiating between the different sleep related processes in children.