In addition to the maturation of endocrine and reproductive systems, puberty in human adolescents is associated with changes in the temporal patterns of several physiological and behavioral events. One of the most prominent behavioral changes is an alteration in sleep organization, specifically a delay in the timing of nocturnal sleep (Strauch & Meier, 1988; Carskadon, Vieira, & Acebo, 1993). Epidemiologic data demonstrate that length of nocturnal sleep declines across adolescence. Most older teenagers report that their sleep patterns on weekdays have an increasingly delayed time of sleep onset, yet they are constrained to wake up early due to school demands. On weekends, when school constraints are not present, sleep onset and sleep offset are delayed. This adolescent delay of the sleep-wake schedule is also associated with a more evening-type preference (Andrade, Benedito-Silva, & Menna-Barreto, 1992; Carskadon et al., 1993).

Although social factors are clearly important in the evolving sleep-wake pattern of adolescents, available evidence implicates peripubertal changes in physiologic mechanisms controlling the timing of sleep. Current models of these mechanisms allow two broad hypotheses: either the circadian system regulating sleep timing is altered to produce a delayed entrained phase position, or homeostatic processes are changed to delay sleep times relative to the circadian oscillator (Borbely, Achermann, Trachsel, & Tobler, 1989). This latter hypothesis remains largely unexplored and is not addressed here.