Dream...

Dreams are the images, thoughts and feelings experienced while sleeping, particularly strongly associated with rapid eye movement sleep. The contents and biological purposes of dreams are not fully understood, though they have been a topic of speculation and interest throughout recorded history. The scientific study of dreams is known as oneirology.

Neurology of sleep and dreams

There is no universally agreed biological definition of dreaming. General observation shows that dreams are strongly associated with rapid eye movement (REM) sleep, during which an electroencephalogram shows brain activity to be most like wakefulness. Participant-nonremembered dreams during non-REM sleep are normally more mundane in comparison. During a typical lifespan, a human spends a total of about six years dreaming (which is about 2 hours each night). It is unknown where in the brain dreams originate, if there is a single origin for dreams or if multiple portions of the brain are involved, or what the purpose of dreaming is for the body or mind. It has been hypothesized that dreams are the result of naturally occurring dimethyltryptamine (DMT) in the brain.[citation needed]

During REM sleep, the release of certain neurotransmitters is completely suppressed. As a result, motor neurons are not stimulated, a condition known as REM atonia. This prevents dreams from resulting in dangerous movements of the body.

Studies show that various species of mammals and birds experience REM during sleep.

Dream content

From the 1940s to 1985, Calvin S. Hall collected more than 50,000 dream reports at Western Reserve University. In 1966 Hall and Van De Castle published The Content Analysis of Dreams in which they outlined a coding system to study 1,000 dream reports from college students. It was found that people all over the world dream of mostly the same things. Hall's complete dream reports became publicly available in the mid-1990s by Hall's protégé William Domhoff, allowing further different analysis.

Personal experiences from the last day or week are frequently incorporated into dreams.

Emotions

The most common emotion experienced in dreams is anxiety. Negative emotions are more common than positive ones. The U.S. ranks the highest amongst industrialized nations for aggression in dreams with 50 percent of U.S. males reporting aggression in dreams, compared to 32 percent for Dutch men.

Sexual content

The Hall data analysis shows that sexual dreams occur no more than 10 percent of the time and are more prevalent in young to mid teens. Another study showed that 8% of men's and women's dreams have sexual content. In some cases, sexual dreams may result in orgasm or nocturnal emission. These are commonly known as wet dreams.

Recurring dreams

While the content of most dreams is dreamt only once, many people experience recurring dreams—that is, the same dream narrative is experienced over different occasions of sleep. Up to 70% of females and 65% of males report recurrent dreams.

Common themes

Content-analysis studies have identified common reported themes in dreams. These include: situations relating to school, being chased, running slowly in place, sexual experiences, falling, arriving too late, a person now alive being dead, teeth falling out, flying, embarrassing moments, falling in love with random people, failing an examination, not being able to move, not being able to focus vision and car accidents. Twelve percent of people dream only in black and white.