A dream is a succession of s, dynamic scenes and situations, ideas, emotions, and sensations that usually occur involuntarily in the mind during certain stages of sleep. Humans generally spend more than two hours dreaming per night, and each dream lasts around 5–20 minutes.
The content and function of dreams have been topics of scientific, philosophical and religious interest throughout recorded history. Dream interpretation, practiced by the Babylonians in the third millennium BCE and even earlier by the ancient Sumerians, figures prominently in religious texts in several traditions, and has played a lead role in psychotherapy. Dreamwork is similar, but does not seek to conclude with definite meaning. The scientific study of dreams is called oneirology. Most modern dream study focuses on the neurophysiology of dreams and on proposing and testing hypotheses regarding dream function. It is not known where in the brain dreams originate, if there is a single origin for dreams or if multiple regions of the brain are involved, or what the purpose of dreaming is for the body (or brain or mind).
The human dream experience and what to make of it has undergone sizable shifts over the course of history. Long ago, according to writings from Mesopotamia and Ancient Egypt, dreams dictated post-dream behaviors to an extent that was sharply reduced in later millennia. These ancient writings about dreams highlight visitation dreams, where a dream figure, usually a deity or a prominent forebear, commands the dreamer to take specific actions, and which may predict future events.Dodds (1951), referring to the type of dream described by Macrobius: "This last type is not, I think, at all common in our own dream-experience. But there is considerable evidence that dreams of this sort were familiar in antiquity." (p. 107). Framing the dream experience varies across cultures as well as through time.
Dreaming and sleep are intertwined. Dreams occur mainly in the rapid-eye movement (REM) stage of sleep—when brain activity is high and resembles that of being awake. Because REM sleep is detectable in many species, and because research suggests that all mammals experience REM, linking dreams to REM sleep has led to conjectures that animals dream. However, humans dream during non-REM sleep, also, and not all REM awakenings elicit dream reports. To be studied, a dream must first be reduced to a verbal report, which is an account of the subject's memory of the dream, not the subject's dream experience itself. Therefore, dreaming by non-humans is currently unprovable, as is dreaming by human fetuses and pre-verbal infants.
Etymology In Old English, the word drēam was used to describe "noise", "joy", or "music", but not related to the sleep-induced brain activity. It was only in the 13th century that the word dream was used to describe "a series of thoughts, images or emotions occurring during sleep". Etymologists believe that this change was influenced due to the Old Norse draumr, which had the same meaning as the word dream nowadays.
Subjective experience and content
Preserved writings from early Mediterranean civilizations indicate a relatively abrupt change in subjective dream experience between Bronze Age antiquity and the beginnings of the classical era.
In visitation dreams reported in ancient writings, dreamers were largely passive in their dreams, and visual content served primarily to frame authoritative auditory messaging. Gudea, the king of the Sumerian city-state of Lagash (reigned 2144–2124 BCE), rebuilt the temple of Ningirsu as the result of a dream in which he was told to do so. After antiquity, the passive hearing of visitation dreams essentially gave way to visualized narratives in which the dreamer becomes a character who actively participates.
From the 1940s to 1985, Calvin S. Hall collected more than 50,000 dream reports at Western Reserve University. In 1966, Hall and Robert Van de Castle published The Content Analysis of Dreams, outlining a coding system to study 1,000 dream reports from college students.Hall, C., & Van de Castle, R. (1966). The Content Analysis of Dreams. New York: Appleton-Century-Crofts. Content Analysis Explained Results indicated that participants from varying parts of the world demonstrated similarity in their dream content. The only residue of antiquity's authoritative dream figure in the Hall and Van de Castle listing of dream characters is the inclusion of God in the category of prominent persons. Hall's complete dream reports were made publicly available in the mid-1990s by his protégé William Domhoff. More recent studies of dream reports, while providing more detail, continue to cite the Hall study favorably.
In the Hall study, the most common emotion experienced in dreams was anxiety. Other emotions included abandonment, anger, fear, joy, and happiness. Negative emotions were much more common than positive ones. The Hall data analysis showed that sexual dreams occur no more than 10% of the time and are more prevalent in young to mid-teens. Another study showed that 8% of both men's and women's dreams have sexual content.Zadra, A., "1093: Sex dreams: what do men and women dream about?" , Sleep Volume 30, Abstract Supplement, 2007 A376. In some cases, sexual dreams may result in orgasms or nocturnal emissions. These are colloquially known as "wet dreams".
The visual nature of dreams is generally highly phantasmagoric; that is, different locations and objects continuously blend into each other. The visuals (including locations, people, and objects) are generally reflective of a person's memories and experiences, but conversation can take on highly exaggerated and bizarre forms. Some dreams may even tell elaborate stories wherein the dreamer enters entirely new, complex worlds and awakes with ideas, thoughts, and feelings never experienced before the dream.
People who are blind from birth do not have visual dreams. Their dream contents are related to other senses, such as hearing, touch, smell, and taste, whichever are present since birth.
Effects of regional or global catastrophes The COVID-19 pandemic also influenced the content of people's dreams, according to a scientific study of over 15,000 dream reports by Deirdre Barrett. This analysis revealed that themes involving fear, illness, and death were two to four times more prevalent in dreams following the onset of the pandemic than they were before.
Neurophysiology
Dream study is popular with scientists exploring the mind–brain problem. Some "propose to reduce aspects of dream phenomenology to neurobiology." But current science cannot specify dream physiology in detail. Protocols in most nations restrict human brain research to non-invasive procedures. In the United States, invasive brain procedures with a human subject are allowed only when these are deemed necessary in surgical treatment to address medical needs of the same human subject. Non-invasive measures of brain activity like electroencephalogram (EEG) voltage averaging or cerebral blood flow cannot identify small but influential neuronal populations.Hobson, J. A., Pace-Schott, E. F., & Stickgold, R. (2000). "Dreaming and the brain: Toward a cognitive neuroscience of conscious states". Behavioral and Brain Sciences, 23(6), 793–842. Also, fMRI signals are too slow to explain how brains compute in real time.
Scientists researching some brain functions can work around current restrictions by examining animal subjects. As stated by the Society for Neuroscience, "Because no adequate alternatives exist, much of this research must [sic] be done on animal subjects." However, since animal dreaming can be only inferred, not confirmed, animal studies yield no hard facts to illuminate the neurophysiology of dreams. Examining human subjects with brain lesions can provide clues, but the lesion method cannot discriminate between the effects of destruction and disconnection and cannot target specific neuronal groups in heterogeneous regions like the brain stem.
Generation
Denied precision tools and obliged to depend on imaging, much dream research has succumbed to the law of the instrument. Studies detect an increase of blood flow in a specific brain region and then credit that region with a role in generating dreams. But pooling study results has led to the newer conclusion that dreaming involves large numbers of regions and pathways, which likely are different for different dream events.
Image creation in the brain involves significant neural activity downstream from eye intake, and it is theorized that "the visual imagery of dreams is produced by activation during sleep of the same structures that generate complex visual imagery in waking perception."
Dreams present a running narrative rather than exclusively visual imagery. Following their work with split-brain subjects, Gazzaniga and LeDoux postulated, without attempting to specify the neural mechanisms, a "left-brain interpreter" that seeks to create a plausible narrative from whatever electro-chemical signals reach the brain's left hemisphere. Sleep research has determined that some brain regions fully active during waking are, during REM sleep, activated only in a partial or fragmentary way. Drawing on this knowledge, textbook author James W. Kalat explains, "[A] dream represents the brain's effort to make sense of sparse and distorted information.... The cortex combines this haphazard input with whatever other activity was already occurring and does its best to synthesize a story that makes sense of the information." Neuroscientist Indre Viskontas is even more blunt, calling often bizarre dream content "just the result of your interpreter trying to create a story out of random neural signaling."
Theories on function
For many humans across multiple eras and cultures, dreams are believed to have functioned as revealers of truths sourced during sleep from gods or other external entities. Ancient Egyptians believed that dreams were the best way to receive divine revelation, and thus they would induce (or "incubate") dreams. They went to sanctuaries and slept on special "dream beds" in hope of receiving advice, comfort, or healing from the gods. From a Darwinian perspective dreams would have to fulfill some kind of biological requirement, provide some benefit for natural selection to take place, or at least have no negative impact on fitness. Robert (1886),Robert, W. Der Traum als Naturnothwendigkeit erklärt. Zweite Auflage, Hamburg: Seippel, 1886. 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 that were not fully worked up, and (b) ideas that were not fully developed during the day. In dreams, incomplete material is either removed (suppressed) or deepened and included into memory. Freud, whose dream studies focused on interpreting dreams, not explaining how or why humans dream, disputed Robert's hypothesis and proposed that dreams preserve sleep by representing as fulfilled those wishes that otherwise would awaken the dreamer.Rycroft, Charles. A Critical Dictionary of Psychoanalysis. London: Penguin Books, 1995, p. 41. Freud wrote that dreams "serve the purpose of prolonging sleep instead of waking up. Dreams are the GUARDIANS of sleep and not its disturbers."
A turning point in theorizing about dream function came in 1953, when Science published the Aserinsky and Kleitman paper establishing REM sleep as a distinct phase of sleep and linking dreams to REM sleep. Until and even after publication of the Solms 2000 paper that certified the separability of REM sleep and dream phenomena, many studies purporting to uncover the function of dreams have in fact been studying not dreams but measurable REM sleep.
Theories of dream function since the identification of REM sleep include: