FIG. 2.

Effect of stimulant drugs on the sleep-wake cycle in the rat. Data are expressed as the hourly percentage of time spent in wakefulness, NREM and REM sleep. Caffeine (20 mg/kg), methamphetamine (1.5 mg/kg), modafinil (300 mg/kg) or drug vehicle were administered at hours 0, 4, and 8. The unshaded portion of each graph represents the 12-h light phase, whereas the shaded portion represents the first two hours of the dark phase. Values are means ± SEM; n = 7 for vehicle; n = 6 for caffeine, methamphetamine, and modafinil. All three stimulants markedly altered sleep-wake patterns over the 14-h recording period (see text for details).