Topographic differences in the adolescent maturation of the slow wave EEG during NREM sleep

Abstract

Study Objectives: Our ongoing longitudinal study has shown that NREM delta (1-4 Hz) and theta (4-8 Hz) power measured at C3 and C4 decrease by more than 60% between ages 11 and 17 years. Here, we investigate the age trajectories of delta and theta power at frontal, central, and occipital electrodes. Design: Baseline sleep EEG was recorded twice yearly for 6 years in 2 cohorts, spanning ages 9-18 years, with overlap at 12-15 years. Setting: Sleep EEG was recorded in the subjects' homes with ambulatory recorders. Participants: Sixty-seven subjects in 2 cohorts, one starting at age 9 (n = 30) and one at age 12 years (n = 37). Measurements and Results: Sleep EEG recorded from Fz, Cz, C3, C4, and O1 was referred to mastoids. Visual scoring and artifact elimination was followed by FFT power analysis. Delta and theta EEG power declined steeply across this age range. The maturational trajectories of delta power showed a "back to front" pattern, with O1 delta power declining earliest and Fz delta power declining latest. Theta EEG power did not show this topographic difference in the timing of its decline. Delta, and to a lesser extent, theta power became frontally dominant in early adolescence. Conclusions: We maintain our interpretation that the adolescent decline in EEG power reflects a widespread brain reorganization driven by synaptic pruning. The late decline in frontally recorded delta power indicates that plasticity is maintained in these circuits until a later age. Although delta and theta have similar homeostatic properties, they have different age and topographic patterns that imply different functional correlates.