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HEALTH AND SAFETY - STAGES OF HEALTHY SLEEP
Stages of Healthy Sleep
During sleep, we usually pass through five phases of sleep: stages 1, 2, 3, 4 and REM (rapid eye movement) sleep. These stages progress in a cycle from stage 1 to REM sleep, then the cycle starts over again with stage 1. In an eight-hour period of sleep the brain cycles through these stages four or five times. We spend almost 50 percent of our total sleep time in stage 2 sleep, about 20 percent in REM sleep, and the remaining 30 percent in the other stages. Infants, by contrast, spend about half of their sleep time in REM sleep.
- Stage 1 (drowsiness): We drift in and out of sleep for about five to 10 minutes and can be awakened easily. Our eyes move very slowly and muscle activity slows.
- Stage 2 (light sleep): Our eye movements stop and our brain waves (fluctuations of electrical activity that can be measured by electrodes) become slower, with occasional bursts of rapid waves called sleep spindles. Our heart rate slows and body temperature decreases.
- Stages 3 and 4 (deep sleep): In stage 3 sleep, extremely slow brain waves called delta waves begin to appear, interspersed with smaller, faster waves. By Stage 4 the brain produces delta waves almost exclusively. It is very difficult to wake someone during stages 3 and 4, which together are called deep sleep. There is no eye movement or muscle activity. People awakened during deep sleep do not adjust immediately and often feel groggy and disoriented for several minutes after they wake up. Some children experience bedwetting, night terrors or sleepwalking during deep sleep.
Note: While alcohol does help people fall into light sleep, it also robs them of REM and the deeper, more restorative stages of sleep.
Dreams, nightmares and sleep terrors
Dreams have been a source of mystery and controversy for many years. To date, there is no unifying theory on why humans dream.
Some evidence suggests that dreams are the way the brain sorts out memories and emotions. Many experts believe that during rapid-eye-movement (REM) sleep the brain may be searching for solutions to the problems that trouble a person when awake. Research on stress and dreams indicate that when people have trouble recalling details of their dreams, it may be an indication that they are not coping with a stressful situation very well. Conversely, individuals who report that their dreams are vivid and rich in detail appear to be recovering or moving past a stressful situation.
As with files on a computer's hard drive, dreams may be one way of clearing out our mental "in-box." Harvard psychiatrist Robert Stickgold, who has done extensive dream research, believes that during REM sleep the brain is engaged in "cross referencing" and filing away new information. When some new learning or information doesn't fit into an existing file in our memory, the dream seems weird. But when the cross reference is a good one, the brain attaches new information to an existing memory file which can reinforce the memory-as a result, the dream makes sense to the dreamer.
Additional research conducted at the University of Liège in Belgium supports this theory. Researchers found that sleeping after learning a new task reinforces the learning. This research found that the same regions of the brain that show activity while we learn a new task are also active while we dream.
Although many professionals agree with the idea that dreams are a combination of the short-term and long-term memory and provide a way for the mind to restore itself during sleep, some believe that dreams are meaningless. Separate research at Harvard studied infants, who spend up to 90 percent of their day in REM sleep. This research team concluded that dreams act as mental stimulation to prevent humans from waking up, so that they will remain in the restful, restorative state of slumber.
Nightmares are dreams with vivid and disturbing content. They are common in children during REM sleep but usually diminish during adolescence and are rare in adults. They usually involve an immediate awakening and good recall of the dream content. In adults, nightmares often accompany trauma or an acute stress reaction. Recurrent and disturbing dreams that interfere with sleep or psychological functioning should be assessed by a psychiatrist or qualified mental health professional.
Sleep terrors are often described as extreme nightmares. Like nightmares, they are rare for adults. Unlike nightmares, sleep terrors typically occur during non-REM (NREM) sleep. Characteristics of a sleep terror include arousal, agitation, large pupils, sweating and increased blood pressure. The individual appears terrified, screams and is usually inconsolable for several minutes, after which he relaxes and returns to sleep. Sleep terrors usually take place early in the night and may be combined with sleepwalking. The individual typically does not remember, or, has only a vague memory of the experience or the dream itself.
REM sleep behaviors are similar to sleep terrors, but more common in adults. This involves complex, vigorous, thrashing or violent behaviors associated with dreams. Patients with REM sleep behaviors may complain of sleep disruption, violent behavior with injuries to themselves or to their bed partner, or unpleasant and vivid dreams. This condition usually occurs in middle-aged or elderly adults, and about one-third have an associated neurological disease.
By Drew Edwards, MD, EdD
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