In people with Alzheimer's, the earliest symptoms are commonly disruptions in sleep rhythms. These include daytime sleepiness, showing agitation or confusion around dusk, staying awake longer, and waking up often at night. These changes are thought to result from damage to sleep-regulating areas in the brain. Alzheimer patients tend to spend less time in both REM (rapid eye movement) sleep, in which most dreaming occurs, and non-REM (NREM) sleep. But they show the greatest reduction in so-called slow-wave sleep (SWS)—a stage of non-dreaming deep sleep, characterized by slow "delta" brain waves (0.1 to 3.5 Hz)—when day-time memories are consolidated.