On 2015 Mar 11, IRWIN FEINBERG commented:

Crawley et al 1 state that there have been few longitudinal studies of sleep/wake timing across adolescence. They fail to take note of our findings in a ten-year longitudinal study of 93 subjects aged 6-18 years. Sleep EEG was recorded twice yearly on habitual school-night schedules in subjects aged 6-18 years. In addition, weekend recordings with extended time in bed and a follow-up night, were obtained from subjects 9-18 years. Results published thus far could have added perspective to the findings of Cowley et al. In addition to defining the trajectories of NREM delta and theta EEG power 2, 3, their within-night dynamics 4, and their relations to puberty 5 and daytime sleepiness 6, we documented changes in NREM and REM bed schedules and sleep durations 7 that bear directly on the findings of Crowley et al. Our study demonstrated that school-night time in bed decreased by 13 min/year between ages 9-18 yrs (p<0.0001). From an average bedtime of 9:15 PM at age 9 yrs, bedtimes advanced by 13 min/year (p<0.0001), whereas rise times did not change (p=0.11). Sleep latency did not change (p=0.70), but sleep efficiency increased over this age range (p<0.0001). The net result was that total sleep time (TST) decreased by 10 min/yr from 515 min at age 9 to xx min at age 18 (p<0.0001). This TST reduction was not produced by shorter REM and NREM durations, as would be expected if it was the result of sleep deprivation due to restricted time in bed. Instead, TST declined because of a selective reduction of NREM sleep, which declined by 12 min/yr (p<0.0001). REM sleep durations actually increased significantly by 2 min/yr (p<0.0001). This pattern of change cannot be attributed to a phase advance. We interpret it, along with the massive decline in slow wave EEG power, as a manifestation of brain maturation driven by synaptic elimination. In our model, synaptic elimination during adolescence decreases the intensity of waking brain activity (shown also by declining cerebral metabolic rate 8) which decreases the need for NREM dependent recuperation of plastic neuronal systems.

1. Crowley SJ, Van Reen E, LeBourgeois MK, et al. A longitudinal assessment of sleep timing, circadian phase, and phase angle of entrainment across human adolescence. PLoS One 2014;9:e112199.
2. Campbell IG, Feinberg I. Longitudinal trajectories of non-rapid eye movement delta and theta EEG as indicators of adolescent brain maturation. Proc Natl Acad Sci U S A 2009;106:5177-80.
3. Feinberg I, Campbell IG. Longitudinal sleep EEG trajectories indicate complex patterns of adolescent brain maturation. Am J Physiol Regul Integr Comp Physiol 2013;304:R296-303.
4. Campbell IG, Darchia N, Higgins LM, et al. Adolescent changes in homeostatic regulation of EEG activity in the delta and theta frequency bands during non-rapid eye movement sleep. Sleep 2011;34:83-91.
5. Campbell IG, Grimm KJ, de Bie E, Feinberg I. Sex, puberty, and the timing of sleep EEG measured adolescent brain maturation. Proc Natl Acad Sci U S A 2012;109:5740-3.
6. Campbell IG, Higgins LM, Trinidad JM, Richardson P, Feinberg I. The increase in longitudinally measured sleepiness across adolescence is related to the maturational decline in low-frequency EEG power. Sleep 2007;30:1677-87.
7. Feinberg I, Davis NM, de Bie E, Grimm KJ, Campbell IG. The maturational trajectories of NREM and REM sleep durations differ across adolescence on both school-night and extended sleep. Am J Physiol Regul Integr Comp Physiol 2012;302:R533-R40.
8. Chugani HT, Phelps ME, Mazziotta JC. Positron emission tomography study of human brain functional development. Ann Neurol 1987;22:487-97.

On 2015 Mar 11, IRWIN FEINBERG commented:

Crawley et al 1 state that there have been few longitudinal studies of sleep/wake timing across adolescence. They fail to take note of our findings in a ten-year longitudinal study of 93 subjects aged 6-18 years. Sleep EEG was recorded twice yearly on habitual school-night schedules in subjects aged 6-18 years. In addition, weekend recordings with extended time in bed and a follow-up night, were obtained from subjects 9-18 years. Results published thus far could have added perspective to the findings of Cowley et al. In addition to defining the trajectories of NREM delta and theta EEG power 2, 3, their within-night dynamics 4, and their relations to puberty 5 and daytime sleepiness 6, we documented changes in NREM and REM bed schedules and sleep durations 7 that bear directly on the findings of Crowley et al. Our study demonstrated that school-night time in bed decreased by 13 min/year between ages 9-18 yrs (p<0.0001). From an average bedtime of 9:15 PM at age 9 yrs, bedtimes advanced by 13 min/year (p<0.0001), whereas rise times did not change (p=0.11). Sleep latency did not change (p=0.70), but sleep efficiency increased over this age range (p<0.0001). The net result was that total sleep time (TST) decreased by 10 min/yr from 515 min at age 9 to xx min at age 18 (p<0.0001). This TST reduction was not produced by shorter REM and NREM durations, as would be expected if it was the result of sleep deprivation due to restricted time in bed. Instead, TST declined because of a selective reduction of NREM sleep, which declined by 12 min/yr (p<0.0001). REM sleep durations actually increased significantly by 2 min/yr (p<0.0001). This pattern of change cannot be attributed to a phase advance. We interpret it, along with the massive decline in slow wave EEG power, as a manifestation of brain maturation driven by synaptic elimination. In our model, synaptic elimination during adolescence decreases the intensity of waking brain activity (shown also by declining cerebral metabolic rate 8) which decreases the need for NREM dependent recuperation of plastic neuronal systems.

1. Crowley SJ, Van Reen E, LeBourgeois MK, et al. A longitudinal assessment of sleep timing, circadian phase, and phase angle of entrainment across human adolescence. PLoS One 2014;9:e112199.
2. Campbell IG, Feinberg I. Longitudinal trajectories of non-rapid eye movement delta and theta EEG as indicators of adolescent brain maturation. Proc Natl Acad Sci U S A 2009;106:5177-80.
3. Feinberg I, Campbell IG. Longitudinal sleep EEG trajectories indicate complex patterns of adolescent brain maturation. Am J Physiol Regul Integr Comp Physiol 2013;304:R296-303.
4. Campbell IG, Darchia N, Higgins LM, et al. Adolescent changes in homeostatic regulation of EEG activity in the delta and theta frequency bands during non-rapid eye movement sleep. Sleep 2011;34:83-91.
5. Campbell IG, Grimm KJ, de Bie E, Feinberg I. Sex, puberty, and the timing of sleep EEG measured adolescent brain maturation. Proc Natl Acad Sci U S A 2012;109:5740-3.
6. Campbell IG, Higgins LM, Trinidad JM, Richardson P, Feinberg I. The increase in longitudinally measured sleepiness across adolescence is related to the maturational decline in low-frequency EEG power. Sleep 2007;30:1677-87.
7. Feinberg I, Davis NM, de Bie E, Grimm KJ, Campbell IG. The maturational trajectories of NREM and REM sleep durations differ across adolescence on both school-night and extended sleep. Am J Physiol Regul Integr Comp Physiol 2012;302:R533-R40.
8. Chugani HT, Phelps ME, Mazziotta JC. Positron emission tomography study of human brain functional development. Ann Neurol 1987;22:487-97.