Although we are constantly learning more and more about sleep and dreams, we still don’t know exactly why we sleep or why we dream.
For centuries, people believed that the purpose of sleep was to rest the body and the mind. However, in the middle of the twentieth century, researchers began monitoring people’s brains as they slept. They found that both the body and the mind are active during sleep. Sleep isn’t restful at all.
While you sleep, your brain takes stock of your body and makes necessary adjustments and repairs. It releases a growth hormone that repairs damaged tissues. It stimulates your immune system to attack any infections you might have. Your brain’s behavior during sleep resembles to that of a computer which is offline, filing and updating the activities of the day.
Space travel gave researchers the opportunity to study how long periods of isolation affect sleep. They found that the less stimulation you get from other people during the day, the less sleep you need. Scientists believe that there is a sleep control center located at the base of your brain. It is affected by the amount of activity you experience when you are awake. If you experience too much activity, the sleep center becomes overloaded and you become tired. However, if you don’t get enough stimulation from the outside world, something prevents the sleep center from triggering. This could be the reason for some cases of insomnia.
At the beginning of the twentieth century, scientists discovered that the brain gives off electrical impulses. In the 1920s, they began measuring brain waves by attaching electrodes to people’s heads. The impulses were then transferred to electroencephalograms (EECs) that could be read on computer screens.
By studying brain waves during sleep, researchers found that your brain goes through four stages of sleep that follow one after each other in a cycle. The complete cycle repeats four or five times for every eight hours that you sleep.
The First Stage of Sleep (N1)
During the first stage of sleep, which is known as N1, you are in what is known as a hypnagogic state. You are in an in-between state in which you are neither fully conscious nor fully unconscious. You can be wakened very easily, and you may hallucinate.
In N1, your body and mind begin to relax. Your heart and breathing slows down. Your blood pressure and body temperature drop. Your eyes roll from side to side.
You may feel like you are falling. This will cause a sudden muscle contraction that is known as hypnic myoclonia.
If you wake up during this first stage of sleep, you may feel like you haven’t slept at all.
The Second Stage of Sleep (N2)
During the second sleep stage, known as N2, you become less aware of what is happening in the waking world around you. Your heart and respiratory rates slow down even more. Your eyes keep rolling from side to side. Your muscles alternately clench and relax.
The next sleep stage, N3, is the stage of deep sleep.
During this time, it is difficult for you to be awakened. If you do wake up, you may feel disoriented.
You have entered a state of deep sleep.
During deep sleep, tissue is repaired and regenerated and you experience bone and muscle growth. Scientists believe that your immune system becomes stronger during deep sleep.
You may wet the bed, sleepwalk or have night terrors.
Before 2007, N3 was divided into two separate stages that were known as Stage 3 and Stage 4. Now, dream researchers consider this to be a single stage.
At the end of N3, you move back to stage N2. The whole process takes about 90 minutes. You then enter a phase known as rapid eye movement (REM) sleep.
REM sleep was discovered in 1953 by Eugene Aserinksy and Nathaniel Kleitman of the University of Chicago. It gets its name from the fact that your eyes dart around rapidly under your closed eyelids. The other four stages of sleep are called, collectively, NREM (non-rapid eye movement) sleep.
During REM sleep, your heart rate and breathing speed up. Your blood pressure increases. Your face and hands twitch. You may have a penile or clitoral erection.
People who are awakened during REM sleep will usually say that they have been dreaming. Most of the dreams that you remember will take place during this stage.
REM sleep is sometimes called “paradoxical sleep” because the brain is very active but the major voluntary muscle groups are paralyzed. You may experience sleep paralysis if you wake up during REM sleep.
In the 1960s, some dream researchers, including psychophysiologist Fred Snyder, suggested that the brain’s high level of activity during REM sleep meant that the purpose of REM sleep was to keep the brain active. They thought that if most of the areas of your brain shut down completely every time you were asleep, they would lose the ability to work when you were awake.
Although REM sleep is often associated with dreaming, you can dream during NREM sleep, too. NREM dreams tend to be less vivid than REM dreams, but this is not always the case.
How Important is Sleep and Dreaming?
Studies of animals that have been deprived of sleep indicate that we need sleep to live. For example, rats normally live for two to three years. If they are deprived of REM sleep, they will live for an average of about five weeks. If they are deprived of all sleep, they will live for about three weeks.
People who are deprived of sleep have short attention spans problems with short-term memory, and difficulty making judgments. If someone is deprived of REM sleep, they are likely to become anxious and irritable, and to have problems concentrating. It is believed that people who are deprived of the ability to dream at night may have dreamlike experiences during the day.