Sleeping and Dreaming

Sleeping and Dreaming Cheryl Kirstein University of South Florida, Tampa, USA ã 2007 Elsevier Inc. All rights reserved.

Several stages of sleep have been described. These include alpha, beta, theta, stage 2, delta (3 and 4), and rapid eye movement (REM).

Fig. 1 Reprinted from Human Physiology, Davies, Copyright 2001, with permission from Elsevier.

Alpha waves are seen in the electroencephalogram (EEG) during a normal wakeful state where the subject is quietly resting. Beta EEG are present when a person is alert/ attentive and thinking actively. Theta rhythm (Stage 1) of sleep is present during the transition from wakefulness to sleep. Stage 2 is defined by alternating patterns of activity. Delta sleep (Stages 3 and 4), which is darting slow-wave sleep (SWS), is the stage during which a person has twitching hands and feet and can experience nightmares. REM sleep is called paradoxical sleep because, during this stage, the EEG appears similar to that of a person who is awake. Someone awakened during REM sleep is alert and responds to meaningful stimuli (not necessarily background noise). A person cycles through these stages and REM approximately every 90 minutes. Sleep is an active process that is characterized by an increase in cerebral blood flow and oxygen consumption. Moreover, the entire body is active during sleep. As subjects report dreams when awakened, it is not considered unconsciousness. The duration of REM sleep in mammals decreases as a function of age. Sleep is adaptive because it prevents an animal from wasting energy at a time of day when nutrients may not be available and when predators may be. It is essential for restoration and repairing tissue, whereas exercise increases SWS, decreased activity does not decrease sleep. Depriving subjects of sleep impairs cerebral functioning and 1