In healthy people, both sleepiness and vigilance show a relationship with core body temperature and skin temperature. When core body temperature is high during the daytime, skin temperature is low, which translates into optimal vigilance. Conversely, when core body temperature is low at night time, skin temperature is high, which correlates to optimal sleep. Among those suffering from narcolepsy, however, direct manipulations of their skin and core body temperatures affect their vigilance and sleepiness, according to a new study.