cents showed spikes of cortisol, the stress hormones, before they went to sleep. And even after they were in deep sleep, they still secreted cortisol, Dahl said.

As noted by Blum, puberty may start early, activating new drives, impulses, emotions, and motivations creating new challenges for the cognitive-emotional interface. Adolescents must develop more self-control over behavior and emotions that involve the prefrontal cortex, one of the last areas of the brain to develop. There is no evidence that the front part of the brain is maturing any faster now than it did throughout human history, according to Dahl. Yet the age of onset of puberty has declined, creating an enormous period of vulnerability as young people face the cognitive and emotional challenges of puberty earlier with relatively less cognitive maturity. All this is occurring in a social context today that gives adolescents a great deal of personal freedom, complex choices, and relatively few constraints.

Automobile fatalities associated with sleepiness alone as well as sleepiness in combination with alcohol use are a major concern. Analysis of data from the National Highway Traffic Safety Administration estimates that up to 100,000 police-reported crashes annually are related to drowsiness (Knipling and Wang, 1995); among drivers age 15 to 24, more than 1,500 fatalities each year are associated with such crashes. (National Highway Traffic Safety Administration, 1999). Research in North Carolina indicates that such crashes tend to be single-vehicle accidents, both for all drivers and for those under 26 (at least those that get codified by law enforcement). Such crashes tend to occur at night, corresponding to the adolescent circadian profile with its afternoon peak in alertness, which may prompt teens to stay out later. They are more likely to occur in males than females (Pack et al., 1995). These accidents are virtually as severe as those involving alcohol; the likelihood of disabling injury or death is similar, unlike the effects of accidents involving seizures or heart attack. In fall-asleep crashes, there tends to be no compensatory response to right the vehicle (Wang et al., 1996).