Sleep EEG, the clearest window through which to view adolescent brain development.

1287 Commentary—Colrain and Baker data showing differences between 15-16 and 17-18 years, with those collected in a similar design but from younger adolescents highlights the fact that later adolescents are still showing dramatic changes in sleep EEG power, reflecting ongoing changes in brain development. Tarokh et al. show smaller changes in the occipital (particularly left occipital) derivations than in the central derivations, and inspection of their figures reveals that the power spectrum at the 15-16 year time point is already at the relatively lower level seen centrally at ages 16-18. This would imply that the occipital cortex develops earlier than regions sampled by central electrodes, consistent with the report by Baker et al. 8 that the occipital derivation showed greater decline than central and frontal derivations across the power spectrum in NREM and REM sleep, when looking at longitudinal changes earlier in adolescence. It is also consistent with the recent Feinberg paper 9 showing an earlier start to the decline in NREM delta for occipital than for central or frontal derivations. Of particular interest in the report by Tarokh et al. is the lack of change in the high sigma band. While this may be, as they suggest, due to a change in the dominant frequency in the band, it may also reflect that neural mechanisms underlying sigma activity (and by extension, sleep spindles) develop early, an interesting implication given their sleep protective role. Baker et al. 8 found no change in the sigma band during NREM sleep, in a longitudinal assessment of younger adolescents. Menstrual phase effects on sigma activity, particularly fast sigma, 10,11 are a potential confound in these sorts of data sets however, particularly when as in the case of the Tarokh et al. paper, the majority of subjects are female. As pointed out by Tarokh and colleagues, the rate of decline in sleep EEG power over time was variable between individuals and unrelated to age at initial assessment. Further studies are needed to investigate what factors contribute to this variability in development in healthy adolescents and extend to investigate whether medical or psychiatric conditions impact changes in the sleep EEG across adolescence. EEG power reflects the sum of inhibitory and excitatory postsynaptic potentials in thousands of neural columns sampled by an individual electrode, 12 and the curve describing changes in delta EEG over the lifespan is remarkably similar to those based on postmortem anatomic synaptic density …