Later onset of alertness and slower accumulation of sleep need in adolescence.

is relayed to the SCN by way of the retino-hypothalamic pathway, the hypothalamus establishes body process patterns in accordance with the day-night cycle. Those processes include brain wave activity, hormone production, cell regeneration—and sleeping and waking times.

In teens, however, Process C is set to a later clock time, enabling them, as we well know, to sleep late in the morning even though it’s light outside. While Process C causes most adults to experience robust alertness during the day and the strongest need for sleep between 2:00 a.m. and 4:00 a.m., teens’ sleep phase delay causes their strongest dip in alertness to be between 3:00 and 7:00 a.m. and can make that dip last until 9:00 or 10:00 a.m. if the teens are sleep deprived. If it’s hard



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