Dreaming and the Brain--The Stages of Sleep

[Dreaming]

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Dreaming and the Brain

When we sleep, we go through five sleep stages. The first stage is a very light sleep from which it is easy to wake up. The second stage moves into a slightly deeper sleep, and stages three and four represent our deepest sleep. Our brain activity throughout these stages is gradually slowing down so that by deep sleep, we experience nothing but delta brain waves -- the slowest brain waves (see "Brain Waves" sidebar). About 90 minutes after we go to sleep and after the fourth sleep stage, we begin REM sleep.

Rapid eye movement (REM) was discovered in 1953 by University of Chicago researchers Eugene Aserinsky, a graduate student in physiology, and Nathaniel Kleitman, Ph.D., chair of physiology. REM sleep is primarily characterized by movements of the eyes and is the fifth stage of sleep.

During REM sleep, several physiological changes also take place. The heart rate and breathingquickens, the blood pressure rises, we can't regulate our body temperature as well and our brain activity increases to the same level (alpha) as when we are awake, or even higher. The rest of the body, however, is essentially paralyzed until we leave REM sleep. This paralysis is caused by the release of glycine, an amino acid, from the brain stem onto the motoneurons (neurons that conduct impulses outward from the brain or spinal cord). Because REM sleep is the sleep stage at which most dreaming takes place, this paralysis could be nature's way of making sure we don't act out our dreams. Otherwise, if you're sleeping next to someone who is dreaming about playing kickball, you might get kicked repeatedly while you sleep.

The four stages outside of REM sleep are called non-REM sleep (NREM). Although most dreams do take place during REM sleep, more recent research has shown that dreams can occur during any of the sleep stages. Tore A. Nielsen, Ph.D., of the Dream and Nightmare Laboratory in Montreal, refers to this as "covert REM sleep" making an appearance during NREM sleep. Most NREM dreams, however, don't have the intensity of REM dreams.

Throughout the night, we go through these five stages several times. Each subsequent cycle, however, includes more REM sleep and less deep sleep (stage three and four). By morning, we're having almost all stage one, two and five (REM) sleep.

Let's look at what happens if you don't get any REM sleep.

BRAIN WAVES

Our brains cycle through four types of brain waves, referred to as delta, theta, alpha and beta. Each type of brain wave represents a different speed of oscillating electrical voltages in the brain. Delta is the slowest (zero to four cycles per second) and is present in deep sleep. Theta (four to seven cycles per second) is present in stage one when we're in light sleep. Alpha waves, operating at eight to 13 cycles per second, occur during REM sleep (as well as when we are awake). And beta waves, which represent the fastest cycles at 13 to 40 per second, are usually only seen in very stressful situations or situations that require very strong mental concentration and focus. These four brain waves make up the electroencephalogram (EEG).

DREAM FACTS

• Most dreams last anywhere from five to 20 minutes.
• People don't only dream in black and white, as was once believed.
• Even though they may not remember them, everyone dreams several times a night. In fact, during a typical lifetime, we spend about six years dreaming.
• People who have been blind from birth have dreams that are formed from their other senses (e.g., touch, smell, sound).
• When people are snoring, they're not dreaming.
• Elephants (and some other animals) sleep standing up during non-REM sleep, but lie down for REM sleep.

Dreams and REM Sleep

What happens if you don't get any REM sleep? Originally, researchers thought that no REM sleep meant no dreams. They theorized that dreams were a sort of safety valve that helped your brain let off steam that you couldn't let off during the day. William Dement, MD, now at Stanford University School of Medicine, did a study in 1960 in which subjects were awakened every time they entered REM sleep. His findings included mild psychological disturbances such as anxiety, irritability and difficulty concentrating. He also noted an increase in appetite. While some studies backed up these ideas, more and more studies did not.

Additional studies tried to make a connection between difficulty remembering things and lack of REM sleep, but those studies too have been disproven with more research. An indisputable snag in the loss-of-memory-function theory was a man who had experienced a brain injury that resulted in him experiencing no REM sleep. He completed law school and had no problems in his day-to-day life.

The latest ideas on REM sleep are associated with learning. Researchers are trying to determine the effects that REM sleep and the lack of REM sleep have on learning certain types of skills -- usually physical skills rather than rote memory. This connection seems strong in some respects due to the fact that infants and toddlers experience much more REM sleep than adults.

Photo courtesy Morguefile

Dream Recall

It is said that five minutes after the end of a dream, we have forgotten 50 percent of the dream's content. Ten minutes later, we've forgotten 90 percent of its content. Why is that? We don't forget our daily actions that quickly. The fact that they are so hard to remember makes their importance seem less.

Theories

Freud theorized that we forget our dreams because they contain our repressed thoughts and wishes and so we shouldn't want to remember them anyway. Other research points to the simple reason that other things get in the way. We are forward-thinking by nature, so remembering something when we first wake up is difficult.

L. Strumpell, a dream researcher of the same era as Freud, believed that several things contribute to our not being able to remember dreams. For one, he said that many things are quickly forgotten when you first wake up, such as physical sensations. He also considered the fact that many dream images are not very intense and would therefore be easy to forget. Another reason, and probably the strongest of his theories, is that we traditionally learn and remember both by association and repetition. As dreams are usually unique and somewhat vague to begin with, it stands to reason that remembering them could be difficult. For example, if someone speaks a phrase to you that doesn't immediately click with anything in your experience, you might need the person to repeat it in order to remember it or even understand it. Since we can't go back to our dreams to experience something again, details that are out of our realm of experience often escape us.

How to Improve Your Dream Recall

Photo courtesy Morguefile

There are many resources both on the Web and in print that will give you tips on how to improve your recall of dreams. Those who believe we have a lot to learn about ourselves from our dreams are big proponents of dream journals. Here are some steps you can take to increase your dream recall:

• When you go to bed, tell yourself you will remember your dreams. (Author's note: In researching this article, I found that thinking about dreams before I fell asleep actually made me remember having them, so this step did work in my experience.)
• Set your alarm to go off every hour and half so you'll wake up around the times that you leave REM sleep -- when you're most likely to remember your dreams. (Or, drink a lot of water before you go to bed to ensure you have to wake up at least once in the middle of the night!)
• Keep a pad and pencil next to your bed.
• Try to wake up slowly to remain within the "mood" of your last dream.

http://science.howstuffworks.com/life/inside-the-mind/human-brain/d...