For other uses, see Dream (disambiguation).
"The Knight's Dream" by Antonio de Pereda

A dream is a succession of images, sounds or emotions that the mind experiences during sleep.[1] The content and purpose 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.
Contents
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* 1 The cultural meaning of dreaming
* 2 Neurobiology of dreaming
o 2.1 Activation synthesis theory
o 2.2 Continual-activation theory
o 2.3 Dreams as excitations of long-term memory
o 2.4 Dreams for strengthening of semantic memories
o 2.5 Dreams for removing junk
o 2.6 Dreams as resonance in neural circuits
* 3 Psychology of sleep and dreams
o 3.1 Dreams for testing and selecting mental schemas
o 3.2 Evolutionary psychology theories of dreams
o 3.3 Psychosomatic theory
o 3.4 Other hypotheses on dreaming
* 4 Dream content
o 4.1 Emotions
o 4.2 Sexual themes
o 4.3 Recurring dreams
o 4.4 Color vs. black and white
* 5 Dream interpretation
* 6 Relationship with medical conditions
o 6.1 Dreams and psychosis
* 7 Other associated phenomena
o 7.1 Lucid dreaming
o 7.2 Dreams of absent-minded transgression
o 7.3 Dreaming and the "real world"
o 7.4 Recalling dreams
o 7.5 Déjà vu
o 7.6 Apparent precognition
* 8 Popular culture
* 9 See also
* 10 References
* 11 Further reading
* 12 External links

[edit] The cultural meaning of dreaming
Jacob's dream of a ladder of angels

Throughout history, people have sought meaning in dreams or divination through dreams.[2] Dreams have been described physiologically as a response to neural processes during sleep, psychologically as reflections of the subconscious, and spiritually as messages from gods, the deceased, predictions of the future or from the Soul, for symbology is the language of the Soul. Many cultures practice dream incubation, with the intention of cultivating dreams that were prophetic or contained messages from the divine.

Judaism has a traditional ceremony called Hatavat Halom – literally meaning "making the dream a good one." Through this rite disturbing dreams can be transformed to give a positive interpretation by a rabbi or a rabbinic court.[3]
[edit] Neurobiology of dreaming
Main article: REM sleep
EEG showing brainwaves during REM sleep

There is no universally agreed upon biological definition of dreaming. In 1952, Eugene Aserinsky identified and defined rapid eye movement (REM) sleep while working in the surgery of his PhD advisor. Aserinsky noticed that the sleepers' eyes fluttered beneath their closed eyelids, later using a polygraph machine to record their brainwaves during these periods. In one session, he awakened a subject who was wailing and crying out during REM and confirmed his suspicion that dreaming was occurring.[4] In 1953, Aserinsky and his advisor published the ground-breaking study in Science.[5]

Accumulated observation shows that dreams are strongly associated with REM sleep, during which an electroencephalogram (EEG) shows brain activity to be most like wakefulness. Participant-nonremembered dreams during NREM sleep are normally more mundane in comparison.[6] During a typical lifespan, a human spends a total of about six years dreaming[7] (which is about two hours each night).[8] Most dreams last only 5 to 20 minutes.[7] 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.

During REM sleep, the release of the neurotransmitters norepinephrine, serotonin and histamine is completely suppressed.[9][10][11] 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.

According to a report in the journal Neuron, rat brains show evidence of complex activity during sleep, including the activation in memory of long sequences of activity.[12][13] Studies show that various species of mammals and birds experience REM during sleep,[14] and follow the same series of sleeping states as humans.[12]

Despite their power to bewilder, arouse, frighten or amuse, dreams are often ignored in mainstream models of cognitive psychology.[15] As methods of introspection were replaced with more self-consciously objective methods in the social sciences in 1930s and 1940s, dream studies dropped out of the scientific literature. Dreams were neither directly observable by an experimenter nor were subjects' dream reports reliable, being prey to the familiar problems of distortion due to delayed recall, if they were recalled at all. According to Sigmund Freud, dreams are more often forgotten entirely, perhaps due to their prohibited character. Altogether, these problems seemed to put them beyond the realm of science.

The discovery that dreams take place primarily during a distinctive electrophysiological state of sleep, rapid eye movement (REM) sleep, which can be identified by objective criteria, led to rebirth of interest in this phenomenon. When REM sleep episodes were timed for their duration and subjects woken to make reports before major editing or forgetting could take place, it was determined that subjects accurately matched the length of time they judged the dream narrative to be ongoing to the length of REM sleep that preceded the awakening. There is no "time dilation" effect; a five-minute dream takes roughly five minutes of real time to play out.[16] This close correlation of REM sleep and dream experience was the basis of the first series of reports describing the nature of dreaming: that it is a regular nightly, rather than occasional, phenomenon, and a high-frequency activity within each sleep period occurring at predictable intervals of approximately every 60–90 minutes in all humans throughout the life span. REM sleep episodes and the dreams that accompany them lengthen progressively across the night, with the first episode being shortest, of approximately 10–12 minutes duration, and the second and third episodes increasing to 15–20 minutes. Dreams at the end of the night may last as long as 15 minutes, although these may be experienced as several distinct stories due to momentary arousals interrupting sleep as the night ends. Dream reports can be reported from normal subjects on 50% of the occasion when an awakening is made prior to the end of the first REM period. This rate of retrieval is increased to about 99% when awakenings are made from the last REM period of the night. This increase in the ability to recall appears to be related to intensification across the night in the vividness of dream imagery, colors and emotions.[citation needed]
[edit] Activation synthesis theory
Main article: Activation-synthesis hypothesis

In 1976 J. Allan Hobson and Robert McCarley proposed a new theory that changed dream research, challenging the previously held Freudian view of dreams as subconscious dreamily wishes to be interpreted. Activation synthesis theory asserts that the sensory experiences are fabricated by the cortex as a means of interpreting chaotic signals from the pons. They propose that in REM sleep, the ascending cholinergic PGO (ponto-geniculo-occipital) waves stimulate higher midbrain and forebrain cortical structures, producing rapid eye movements. The activated forebrain then synthesizes the dream out of this internally generated information. They assume that the same structures that induce REM sleep also generate sensory information.

Hobson's 1976 research suggested that the signals interpreted as dreams originated in the brain stem during REM sleep. However, research by Mark Solms suggests that dreams are generated in the forebrain, and that REM sleep and dreaming are not directly related.[17] While working in the neurosurgery department at hospitals in Johannesburg and London, Solms had access to patients with various brain injuries. He began to question patients about their dreams and confirmed that patients with damage to the parietal lobe stopped dreaming; this finding was in line with Hobson's 1977 theory. However, Solms did not encounter cases of loss of dreaming with patients having brain stem damage. This observation forced him to question Hobson's prevailing theory which marked the brain stem as the source of the signals interpreted as dreams. Solms viewed the idea of dreaming as a function of many complex brain structures as validating Freudian dream theory, an idea that drew criticism from Hobson. In 1978, Solms, along with partners William Kauffman and Edward Nadar, undertook a series of traumatic-injury impact studies using several different species of primates, particularly howler monkeys, in order to disprove Hobson's postulation that the brain stem played a significant role in dream pathology. Unfortunately, Solms' experiments proved inconclusive, as the high mortality rate associated with using a hydraulic impact pin to artificially induce brain damage in test subjects meant that his final candidate pool was too small to satisfy the requirements of the scientific method.[18]
[edit] Continual-activation theory

Combining Hobson's activation synthesis hypothesis with Solms' findings, the continual-activation theory of dreaming presented by Jie Zhang proposes that dreaming is a result of brain activation and synthesis; at the same time, dreaming and REM sleep are controlled by different brain mechanisms. Zhang hypothesizes that the function of sleep is to process, encode and transfer the data from the short-term memory to the long-term memory, though there is not much evidence backing up this so-called "consolidation." NREM sleep processes the conscious-related memory (declarative memory), and REM sleep processes the unconscious related memory (procedural memory).

Zhang assumes that during REM sleep, the unconscious part of a brain is busy processing the procedural memory; meanwhile, the level of activation in the conscious part of the brain will descend to a very low level as the inputs from the sensory are basically disconnected. This will trigger the "continual-activation" mechanism to generate a data stream from the memory stores to flow through the conscious part of the brain. Zhang suggests that this pulse-like brain activation is the inducer of each dream. He proposes that, with the involvement of the brain associative thinking system, dreaming is, thereafter, self-maintained with the dreamer's own thinking until the next pulse of memory insertion. This explains why dreams have both characteristics of continuity (within a dream) and sudden changes (between two dreams).[19][20]
[edit] Dreams as excitations of long-term memory

Eugen Tarnow suggests that dreams are ever-present excitations of long-term memory, even during waking life. The strangeness of dreams is due to the format of long-term memory, reminiscent of Penfield & Rasmussen's findings that electrical excitations of the cortex give rise to experiences similar to dreams. During waking life an executive function interprets long-term memory consistent with reality checking. Tarnow's theory is a reworking of Freud's theory of dreams in which Freud's unconscious is replaced with the long-term memory system and Freud's "Dream Work" describes the structure of long-term memory.[21]
[edit] Dreams for strengthening of semantic memories
Location of hippocampus

A 2001 study showed evidence that illogical locations, characters, and dream flow may help the brain strengthen the linking and consolidation of semantic memories. These conditions may occur because, during REM sleep, the flow of information between the hippocampus and neocortex is reduced.[22] Increasing levels of the stress hormone cortisol late in sleep (often during REM sleep) cause this decreased communication. One stage of memory consolidation is the linking of distant but related memories. Payne and Nadal hypothesize that these memories are then consolidated into a smooth narrative, similar to a process that happens when memories are created under stress.[23]
[edit] Dreams for removing junk

Robert (1886),[24] a physician from Hamburg, was the first who suggested that dreams are a need and that they have the function to erase (a) sensory impressions which were not fully worked up and (b) ideas which were not fully developed during the day. By the dream work incomplete material will be either removed or deepened and included into memory. Robert's ideas were cited repeatedly by Freud in his Traumdeutung. Hughlings Jackson (1911) viewed that sleep serves to sweep away unnecessary memories and connections from the day. This was revised in 1983 by Crick and Mitchison's "reverse learning" theory, which states that dreams are like the cleaning-up operations of computers when they are off-line, removing parasitic nodes and other "junk" from the mind during sleep.[25][26] However, the opposite view that dreaming has an information handling, memory-consolidating function (Hennevin and Leconte, 1971) is also common. Dreams are a result of the spontaneous firings of neural patterns while the brain is undergoing memory consolidation during sleep.
[edit] Dreams as resonance in neural circuits

During sleep the eyes are closed, so that the brain to some degree becomes isolated from the outside world. Moreover all signals from the senses (except olfaction) must pass through the thalamus before they reach the brain cortex, and during sleep thalamic activity is suppressed.[27] This means that the brain mainly works with signals from itself. A well-known phenomenon in dynamical physical systems where the level of input and output from the system is low is that oscillation makes spontaneous resonance patterns to occur. Hence, dreams may be the simple consequence of neural oscillation.
[edit] Psychology of sleep and dreams

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[edit] Dreams for testing and selecting mental schemas

Coutts[28] hypothesizes that dreams modify and test mental schemas during sleep during a process he calls emotional selection, and that only schema modifications that appear emotionally adaptive during dream tests are selected for retention, while those that appear maladaptive are abandoned or further modified and tested. Alfred Adler suggested that dreams are often emotional preparations for solving problems, intoxicating an individual away from common sense toward private logic. The residual dream feelings may either reinforce or inhibit contemplated action.
[edit] Evolutionary psychology theories of dreams

Evolutionary psychologists believe that dreams serve some adaptive function for survival. Deirdre Barrett describes dreaming as simply "thinking in different biochemical state" and believes people continue to work on all the same problems—personal and objective—in that state.[29] Her research finds that anything—math, musical composition, business dilemmas—may get solved during dreaming, but the two areas especially likely to help are 1) anything where vivid visualization contributes to the solution, whether in artistic design or invention of 3-D technological devices and 2) problem where the solution lies in "thinking outside the box"—i.e. the person is stuck because conventional wisdom on how to approach the problem is wrong.[30][31] In a related theory, which Mark Blechner terms "Oneiric Darwinism," dreams are seen as creating new ideas through the generation of random thought mutations. Some of these may be rejected by the mind as useless, while others may be seen as valuable and retained.[32] Finnish psychologist Antti Revonsuo posits that dreams have evolved for "threat simulation" exclusively.
[edit] Psychosomatic theory

Dreams are a product of "dissociated imagination," which is dissociated from the conscious self and draws material from sensory memory for simulation, with sensory feedback resulting in hallucination. By simulating the sensory signals to drive the autonomous nerves, dreams can affect mind-body interaction. In the brain and spine, the autonomous "repair nerves," which can expand the blood vessels, connect with compression and pain nerves. Repair nerves are grouped into many chains called meridians in Chinese medicine. When a repair nerve is prodded by compression or pain to send out its repair signal, a chain reaction spreads out to set other repair nerves in the same meridian into action. While dreaming, the body also employs the meridians to repair the body and help it grow and develop by simulating very intensive movement-compression signals to expand the blood vessels when the level of growth enzymes increase.[33]
[edit] Other hypotheses on dreaming

There are many other hypotheses about the function of dreams, including:[34]

* Dreams allow the repressed parts of the mind to be satisfied through fantasy while keeping the conscious mind from thoughts that would suddenly cause one to awaken from shock.[35]
* Freud suggested that bad dreams let the brain learn to gain control over emotions resulting from distressing experiences.[34]
* Jung suggested that dreams may compensate for one-sided attitudes held in waking consciousness.[36]
* Ferenczi[37] proposed that the dream, when told, may communicate something that is not being said outright.
* Dreams regulate mood.[38]
* Hartmann[39] says dreams may function like psychotherapy, by "making connections in a safe place" and allowing the dreamer to integrate thoughts that may be dissociated during waking life.
* More recent research by psychologist Joe Griffin, following a twelve-year review of data from all major sleep laboratories, led to the formulation of the expectation fulfillment theory of dreaming, which suggests that dreaming metaphorically completes patterns of emotional expectation in the autonomic nervous system and lowers stress levels in mammals.[40][41]

[edit] 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.[42] 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.[43]
[edit] Emotions

The most common emotion experienced in dreams is anxiety. Other emotions include pain, abandonment, fear, joy, happiness, etc. Negative emotions are much more common than positive ones.[42]
[edit] Sexual themes

The Hall data analysis shows that sexual dreams occur no more than 10% of the time and are more prevalent in young to mid-teens.[42] Another study showed that 8% of men's and women's dreams have sexual content.[44] In some cases, sexual dreams may result in orgasms or nocturnal emissions. These are colloquially known as wet dreams.[45]
[edit] 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.[citation needed]
[edit] Color vs. black and white

A small minority of people say that they dream only in black and white.[46][47]
[edit] Dream interpretation
Main article: Dream interpretation

Dreams were historically used for healing (as in the asclepieions found in the ancient Greek temples of Asclepius) as well as for guidance or divine inspiration. Some Native American tribes used vision quests as a rite of passage, fasting and praying until an anticipated guiding dream was received, to be shared with the rest of the tribe upon their return.[48]

During the late 19th and early 20th centuries, both Sigmund Freud and Carl Jung identified dreams as an interaction between the unconscious and the conscious. They also assert together that the unconscious is the dominant force of the dream, and in dreams it conveys its own mental activity to the perceptive faculty. While Freud felt that there was an active censorship against the unconscious even during sleep, Jung argued that the dream's bizarre quality is an efficient language, comparable to poetry and uniquely capable of revealing the underlying meaning.

Fritz Perls presented his theory of dreams as part of the holistic nature of Gestalt therapy. Dreams are seen as projections of parts of the self that have been ignored, rejected, or suppressed.[49] Jung argued that one could consider every person in the dream to represent an aspect of the dreamer, which he called the subjective approach to dreams. Perls expanded this point of view to say that even inanimate objects in the dream may represent aspects of the dreamer. The dreamer may therefore be asked to imagine being an object in the dream and to describe it, in order to bring into awareness the characteristics of the object that correspond with the dreamer's personality.