Dr. William A. “Jet” Broughton, professor of internal medicine at the University of South Alabama College of Medicine, said sleep progresses through a number of different stages that are marked by distinctive changes in brain activity.

“You don’t just go to sleep and then wake up in the morning,” said Dr. Broughton, who is board-certified in sleep medicine. “There is a sort of architecture of sleep.”

Research has revealed a 90-minute sleep cycling through non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. REM sleep is when most dreaming occurs. “Every 90 minutes, there is a dream period in normal adult individuals,” Dr. Broughton said. “These dream periods get longer and longer as the night wears on. Thus, early morning awakenings are often accompanied by dream recall.”

The phenomenon of dreaming is generated by a lower portion of the brain called the pons. This area contains the on-off switch for dreaming and also contains the wiring for transmitting commands for muscle activity to the body.

According to Dr. Broughton, REM sleep is associated with eye-movements, thought content and reduced body tone that approaches paralysis. “We lose our muscle tone during REM sleep, resulting in a sort of paralysis,” he said. “This is important because it prevents us from getting up and acting out our dreams while we’re asleep.” In rare cases, Dr. Broughton said this “paralysis” is lost and sleepers act out their dream content, sometimes to the point of injury.

Many have had the experience of waking up from a dream and feeling unable to move. “Sometimes dream content continues,” Dr. Broughton said. “This is called ‘sleep paralysis’ and is usually a normal occurrence.”

Dr. Broughton said early researchers found that dream content is forgotten almost instantaneously in most subjects. “The only dreams we recall are the really good, the really bad, or the really weird ones,” he said.

According to Dr. Broughton, the function of dreaming is still unknown.

Dr. Sigmund Freud’s theory of dreams suggested that dreams were a representation of unconscious desires, thoughts and motivations. Psychiatrist Carl Jung claimed that dream analysis is the primary way to gain knowledge of the unconscious mind. Dr. Broughton said most current thought suggests that dream content is not quite as meaningful as that.

Instead, dreams are believed to be “electrical noise” that may be part of the learning process. “Studies have shown that REM sleep may play a role in consolidating learned material,” Dr. Broughton said. “In one study people were asked to study unfamiliar material and then were divided into two groups – one group was allowed to sleep normally after studying and the other group had their REM sleep physically interrupted. Post-sleep testing showed that the group that had normal sleep remembered more of the studied material than the group that had their REM sleep interrupted."

Dr. Broughton said dreams are not instantaneous occurrences. “Dreams are temporal events,” he said. “This means you can wake up from a dream, go back to sleep, and sometimes pick it up where you left off.” In addition, he said dreams usually only occur at night unless we are sleep deprived. If you are deprived of sleep, the pressure to have dream sleep will move into the daytime.

We are not in control of our dream content, according to Dr. Broughton. “Odd, worrisome and even frightening content should not make us uneasy," he said. "It is just our brain sorting through the events of the day and our life. Think of it as the filing of our memories and feelings in their appropriate place in the cabinet of our memory.”

Dr. Broughton recently gave an overview of sleep medicine – including information on dreams, sleep stages, and obstructive sleep apnea – at the March Med School Café lecture. To view the lecture in its entirety, click here.

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