Childhood and adolescent changes in sleep spindle trends across the night

Study Objectives Sleep spindle trends across sleep cycles provide clues to factors that influence these distinct EEG waveforms. We describe cycle trends in spindle density, frequency, amplitude, and duration, and we determine how these trends change across childhood and adolescence. Furthermore, we test how the trends in spindle density are related to trends in slow wave (delta) EEG incidence. Methods A computer program detected and measured sleep spindles in central and frontal EEG from 1944 nights from our longitudinal dataset of semiannual recordings from 97 participants, ages 6 to 18 years. Results Spindle density and duration increased steeply between cycles 1 and 2 with smaller increases across subsequent cycles. The magnitude of these increases decreased with age. The spindle density cycle trend was strongly related to the delta cycle trend, but the age-related change in the density trend was not related to changes in delta. Spindle wave frequency shifted from an increase across cycles in children to a u-shaped trend in older adolescents, whereas central spindle amplitude shifted from a u-shaped trend to a linear increase. The trends in frontal and central spindles were, on the whole, similar with exceptions suggesting later maturation of frontal circuits. Conclusions The age-related changes in sleep spindle measures across sleep cycles cannot be attributed solely to thalamocortical pruning but must also be affected by myelination and circuit reorganization. The age-related changes in cycle trends for spindle frequency indicate a shift from a strong homeostatic influence in children to greater circadian influence in late adolescence.