The Sleep Cycle
One sleep cycle comprises of four stages and lasts for about 90-120 minutes. Note that some books list five stages in the sleep cycle. These books consider the first five to ten minutes when you are falling asleep as a stage in the sleep cycle. We think this is more of a transitional phase and not really part of the cycle, especially since this stage of sleep does not repeat itself, while the other four stages do repeat themselves throughout the night. For this reason, we have excluded as part of the cycle.
Dreams can occur in any of the four stages of sleep, but the most vivid and memorable dreams occur in the last stage of sleep (also commonly referred to as REM sleep). The sleep cycle repeats itself about an average of four to five times per night, but may repeat as many as seven times. Thus, you can see how a person has several different dreams in one night. However, most people only remember dreams that occur closer toward the morning when they are about to wake up. But just because you can’t remember those dreams do not mean that they never happened. Some people believe that they simply do not dream, when in reality, they just don’t remember their dreams.
The Stages Of Sleep
The stages in the sleep cycle are organized by the changes in specific brain activity.
Stage 1: You are entering into light sleep. This stage is characterized by Non-rapid eye movements (NREM), muscle relaxation, lowered body temperature and slowed heart rate. The body is preparing to enter into deep sleep.
Stage 2: Also characterized by NREM, this stage is characterized by a further drop in body temperature and relaxation of the muscles. The body’s immune system goes to work on repairing the day’s damage. The endocrine glands secrete growth hormones, while blood is sent to the muscles to be reconditioned. In this stage, you are completely asleep.
Stage 3: Still in the NREM stage, this is an even deeper sleep. Your metabolic levels are extremely slow.
Stage 4: In this stage of sleep, your eyes move back and forth erratically as if watching something from underneath your eyelids. Referred to as REM sleep or delta sleep, this stage occurs at about 90-100 minutes after the onset of sleep. Your blood pressure rises, heart rate speeds up, respiration becomes erratic and brain activity increases. Your involuntary muscles also become paralyzed or immobilized. This stage is the most restorative part of sleep. Your mind is being revitalized and emotions is being fine tuned. The majority of your dreaming occurs in this stage. If you are awakened during this stage of sleep, you are more likely to remember your dreams.
These stages repeat themselves throughout the night as you sleep. As the cycle repeats, you will spend less time in stages 1 to 3 and more time dreaming in stage 4. In other words, it will be quicker and quicker for you to get to stage 4 each time the cycle repeats.
The Mechanics of Dreaming
While you are dreaming, your body undergoes noticeable changes. Your adrenaline rises, your blood pressure increases, and you heart beats faster. Given this hyperactivity, it should be no surprise how someone with a weak heart can die in their sleep. Their heart may not be able to withstand the strain and the erratic changes that their body is going through.
Dreaming takes place during REM, which stands for Rapid Eye Movement. It is thus called, because your eyes move rapidly back and forth under the eyelids. REM sleep takes place in the fourth stage of sleep and accounts for 15-20% of your sleep time. From the point you fall asleep, it takes 30 to 90 minutes before you start dreaming. You cycle through the 4 stages of sleep and may enter the REM stage 4 to 7 times in one night. During REM, your blood pressure and heart rate fluctuate and increase. It sounds like your body is going through a lot, but in fact, it is quite the contrary. During REM, your bodies are completely immobile and your muscles remain completely relaxed. You may shift in your bed throughout the night, but when in REM, you are completely still. This is commonly known as “REM Paralysis”.
In REM sleep, the mind is as active as it is during waking. However, chemically it is different. REM is controlled by the excitability level of the cholinergic neurons. Noradrenaline and seratonin are missing in the brain when in the dream state. These chemicals allow the brain to carry out task, solve problems and remember things. This is a reason why you find it so hard to remember your dreams.
The Importance Of Dreaming
Do you dream in order to sleep or do you sleep in order to dream? Although that question remains debatable, researchers agree that there is a purpose and importance to dreaming.
Research have showed that people who are deprived from entering the dream phase of sleep or the REM stage, exhibit symptoms of irritability and anxiety. In one dream study, volunteers are woken up right before they enter into the dream state. Then they are allowed to fall back to sleep. Again, right before they enter REM sleep, they are awaken. This continues on through the night. The volunteers sleep the same amount of time as they normally do. The next day, these volunteers go about their day and observed to be disoriented, depressed, crabby, and quick tempered. There is a general impairment in their daily functioning. Some eat more than usual. As this study continues on through several nights, subjects become more and more agitated. It is found that deprivation of REM sleep causes over-sensitivity, lack of concentration and memory loss.
This study shows the importance of dreaming and its role in your well-being and health. Some researchers believe that dreams help you to tackle stress. Dreaming is a necessity and helps to recharge the mind and revitalize the body.
Babies And Dreams
In a study on babies and dreaming, it was learned that babies spend about 66% of their sleeping time in the REM state. That is quite a bit of dreaming, considering that the average adult spends 15-20% of their sleep time in the dreaming stage. Dream researchers believe that there is a correlation between REM sleep and brain development. While still in the womb, the fetus is already spending a significant amount of time in REM sleep. At only 30 weeks, the fetus spends nearly 24 hours in the REM state.
Premature babies also spend up to 80% of their sleep in the REM state. As babies mature, their REM sleep decreases. It drops to 50% in the full term baby and down to 35% in a one year old. This finding supports the notion that REM sleep is important in the mental development of the baby. Dreaming may be seen as a way of “exercising” the mind and stimulating it. As babies get older, they will be able get mental stimulation from their surroundings and outside environment.
It is difficult to know what babies are dreaming about, but their dreams are probably triggered mainly by physical sensations. As babies continue to develop, visual images and sounds begin to play a role in dreams.
Children And Dreams
In a research conducted at the University of Virginia, it was found that animals are featured more prominently in children’s dreams compared to adults’ dreams. This may be due to the notion that children are just interested in animals. Furthermore, frightening animals, like lions, snakes, crocodiles, and wolves occur more often then non-frightening animals, like sheep, butterflies or birds. Children use animals to symbolize their wishes and fears.
Children also seem to dream more about aggression than adults. Surprisingly children dream about aggressive acts twice as often as adults. This may be due to the notion that children are still trying to control their impulses in order to live and function in a civilized society. They are trying to keep their impulses in check.
Interestingly, the research showed that the dreams of girls were longer than those of boys. Girls’ dreams contained more people and clothing. Boys’ dreams were more about tools and objects.
Children’s nightmares often stem from being punished by parents, when a child is sick or if there is turmoil in the child’s home life.