Understanding Dreams and REM Sleep

Dreams happen during the rapid eye movement (REM) stage of sleep. In a typical night, you dream for a total of two hours, broken up by the sleep cycle. Researchers do not know much about how we dream or why. They do know that newborns dream and that depriving rats of REM sleep greatly shortens their lives. Other mammals and birds also have REM sleep stages, but cold-blooded animals such as turtles, lizards, and fish do not.

Dreams can take place during any of the stages of sleep, but those that occur during REM sleep tend to be the most frequent and vivid.

What is REM sleep? This period of the sleep cycle usually takes place about 90 minutes after a person first falls asleep. It is marked by a number of physiological changes that include muscle relaxation, eye movement, faster respiration, and increased brain activity.

REM sleep usually begins after a period of deep sleep known as stage 3 sleep. An area of the brain called the pons—where REM sleep signals originate—shuts off signals to the spinal cord. That causes the body to be immobile during REM sleep.

When the pons doesn't shut down the spinal cord's signals, people will act out their dreams. This can be dangerous because acting out dreams without input from the senses can lead a person to run into walls, fall down stairs or worse. This condition is rare and different from more common sleepwalking and known as REM sleep behavior disorder.

The pons also sends signals to cerebral cortex by way of the thalamus (which is a filter and relay for sensory information and motor control functions deep in the brain). The cerebral cortex is the part of the brain involved with processing information (learning, thinking, and organizing). The areas of the brain “turned on” during REM sleep seem to help learning and memory. Infants spend almost 50% of their sleep time in REM sleep (compared to 20% for adults), which may be explained by the tremendous amount of learning in infancy.

If people are taught various skills and then deprived of REM sleep, they often cannot remember what they were taught.

Dreams may be one way that the brain consolidates memories. The dream time could be a period when the brain can reorganize and review the day’s events and connect new experiences to older ones. Because the body is shut down, the brain can do this without additional input coming in or risking the body “acting out” the day’s memories.

Some researchers believe that dreams are more like a background “noise” that is interpreted and organized. This activation-synthesis theory states that dreams are merely the brain’s attempt to make sense of random signals occurring during sleep. Some people have more control over their dreams than others. For these people, the last thoughts before going to bed may influence the content of a dream.

You can develop your ability to remember your dreams by keeping a journal near your bed and writing down everything you can about your dreams when you first wake up. After a few weeks, your ability to remember your dreams will improve. Some people claim that they have lucid dreams, which are dreams in which they can participate and change the dream as it develops. Lucid dreaming can be triggered through a number of techniques, though little research and lots of speculation have been done on it.