Understanding Psychology (10th Ed)

142 Chapter 
5 
States of Consciousness
The Stages of Sleep
Most of us consider sleep a time of tranquility when we set aside the tensions of the 
day and spend the night in uneventful slumber. However, a closer look at sleep 
shows that a good deal of activity occurs throughout the night. 
Measures of electrical activity in the brain show that the brain is quite active 
during the night. It produces electrical discharges with systematic, wavelike patterns 
that change in height (or amplitude) and speed (or frequency) in regular sequences. 
There is also signifi cant physical activity in muscle and eye movements. 
People progress through a series of distinct stages of sleep during a night’s rest— 
known as stage 1 through stage 4 and REM sleep —moving through the stages in cycles 
lasting about 90 minutes. Each of these sleep stages is associated with a unique pat-
tern of brain waves, which you can see in Figure 2. 
When people fi rst go to sleep, they move from a waking state in which they are 
relaxed with their eyes closed into  stage 1 sleep  , which is characterized by relatively 
rapid, low-amplitude brain waves. This is actually a stage of transition between 
wakefulness and sleep and lasts only a few minutes. During stage 1, images some-
times appear, as if we were viewing still photos, although this is not true dreaming, 
which occurs later in the night.
As sleep becomes deeper, people enter  stage 2 sleep  , which makes up about 
half of the total sleep of those in their early 20s and is characterized by a slower, 
more regular wave pattern. However, there are also momentary interruptions of 
sharply pointed, spiky waves that are called, because of their confi guration, sleep 
spindles . It becomes increasingly diffi cult to awaken a person from sleep as stage 2 
progresses.
As people drift into  stage 3 sleep , the brain waves become slower, with higher 
peaks and lower valleys in the wave pattern. By the time sleepers arrive at  stage 4