THE BLOG
01/08/2015 08:19 am ET Updated Mar 10, 2015

Our Dreaming World

Dreaming is a fundamental, seemingly timeless part of the human experience. For many thousands of years, humans have contemplated, theorized about, and given meaning to dreams. Ancient cultures paid great attention to dreams. Among diverse ancient cultures, dreams took on many forms of meaning and significance. Sometimes dreams were warnings and messages from gods or divine entities. In some cases, dreams might be evidence of evil spirits. Dreams were considered a vehicle for predicting the future, a way to communicate with the dead, a means to travel beyond the physical limits of the body. Dreams were believed to be both powerful and important.

In the 19th and early 20th centuries, physicians exploring the complicated emotional landscape of the human experience gave tremendous attention and significance to dreams. Sigmund Freud believed dreams were the necessary expression of the unconscious mind, a vehicle for the mind to explore repressed emotions and desires. Carl Jung theorized that dreams provided a means to resolve conflicts between an individual's conscious and unconscious mind, conflicts that reflected the tensions of both the individual's internal sense of self and a sense of self in society. By the mid-20th century, scientists were engaged in study of the cognitive and neurological mechanisms of dreaming, one part of a broader scientific exploration of sleep. Today, new technologies enable us to observe and explore dreaming states in whole new ways.

Yet dreaming remains in many ways a deep mystery. Despite sustained scientific exploration and attention -- and no shortage of theories -- we still don't know the answer to the most fundamental question: Why do we dream? For all the study and attention that dreams have received, its rather remarkable how much we don't know about dreaming -- not only about its purpose, but also about the mechanics in the brain that make dreams happen.

In this three-part series, we'll explore the world of dreams, looking at the latest science has to say about why we might dream, and the mechanics of dreaming in the brain. We'll examine the content of dreams, and how dreams may both reflect and influence waking life. We'll look at disorders related to dreaming, and how health conditions and some medication can disrupt dreams.

First up: the basics. What is a dream, exactly, and what are the characteristics of typical dream behavior?

At its most basic level, a dream is a collection of images, impressions, events and emotions that we experience during sleep. Sometimes dreams have strong narratives, with plots and characters that could be plucked from a movie screen. Other times dreams are more impressionistic, with emotions or visual imagery as the most identifiable characteristic. How and why dreams occur is still very much up for inquiry and debate. But there are some details about dreaming that we do know.

Typically, a person will spend two hours or more a night dreaming, experiencing somewhere in the range of 3-6 discrete dreams over the course of a night's rest. The length of dreams can vary significantly, but most dreams appear to last from 5-20 minutes. The vast majority of dreams we experience will -- for most of us -- never be remembered. Memories of dreams usually fade very quickly after we awaken. But the degree to which we remember our dreams -- or don't remember -- is not a reflection of how much time we actually spend dreaming.

Our individual capacity to recall dream varies widely. Some people can regularly remember dreams, often with great detail, while others may have only hazy recollections of themes or subjects in their dreams -- or no recollection at all. There are a number of possible explanations for why some people are more or less able to remember their dreams. Studies suggest dream recall may be linked to patterns of activity in the brain. Other research indicates dream recall may be influenced by interpersonal attachment styles -- the way we tend to form bonds with other people in our lives. The fluctuations of hormone levels throughout the night might also have a role in dream recall. During REM sleep -- a time of active dreaming -- levels of the hormone cortisol are high, and may interfere with communication between areas of the brain that are involved in memory consolidation.

Much -- but not all -- dreaming appears to occur during REM sleep. This stage of sleep is characterized by high levels of brain activity, similar to what occurs during a state of wakefulness. Adults spend roughly 25 percent of their sleep time in REM sleep, with longer periods of REM sleep occurring later in the night and in the early morning. REM sleep is part of the normal sleep cycle that also includes several other stages of non-REM (NREM) sleep -- stages 1-3, with stages 1 and 2 being light sleep and stage 3 consisting of deep sleep. Dreaming can occur in every stage of sleep. Research suggests that both the mechanisms of dreaming in the brain and the dream experience itself are strikingly different in REM sleep versus NREM sleep. Dreams during REM sleep appear to be considerably more visually vivid, bizarre, and narratively-driven than dreams during other sleep stages.

An important characteristic of REM sleep that relates to dreaming is a condition known as REM atonia, the immobilization of most of the body's major muscle groups and reflexes. During REM sleep, the body becomes largely paralyzed, in what appears to be at least in part a protective response to the emotionally and physically charged nature of dreaming. REM atonia keeps the sleeper from acting out physically in response to dreams. It's possible to awaken and still be in a state of sleep paralysis. This can be a deeply frightening experience, particularly the first time it occurs. When this happens, you may be unable to speak or to move for a brief period of time. Waking to experience sleep paralysis is a sign that your body may not be making smooth transitions between the stages of sleep. This can be the result of stress, sleep deprivation, other sleep disorders including narcolepsy, as well as a side effect of medications or over-consumption of drugs or alcohol.

Now that we've covered some of what's understood about the mechanics of dreaming, we'll next look at the stuff of which dreams are made: dream content, and the characteristics of the dreaming experience.

Sweet Dreams,

Michael J. Breus, PhD
The Sleep Doctor™
www.thesleepdoctor.com

Also on HuffPost:

PHOTO GALLERY
5 Things Your Dreams Can Tell You About Your Health