Editing Dream (section)

== Theories on function ==
{{Main|Oneirology}}
{{Further|Rapid eye movement sleep}}

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.<ref>{{Cite book |last=Ribeiro |first=Sidarta |url=https://www.worldcat.org/oclc/1200037413 |title=The oracle of night : the history and science of dreams |date=2021 |others=Daniel Hahn, Sidarta Translation of: Ribeiro |isbn=978-1-5247-4690-2 |edition= |location=New York |oclc=1200037413}}</ref> 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.<ref name="Krippner1"/> 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),<ref>Robert, W. Der Traum als Naturnothwendigkeit erklärt. Zweite Auflage, Hamburg: Seippel, 1886.</ref> 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. [[Sigmund Freud|Freud]], whose dream studies focused on interpreting dreams, not explaining how or why humans dream, disputed Robert's hypothesis<ref>{{cite book |last=Freud |first=Sigmund |translator=James Strachey |editor=James Strachey |author-link=Sigmund Freud |date=1965 |title=The Interpretation of Dreams |page=188 |location=New York |publisher=Avon |quote=The view adopted by Robert [1886, 9 f.] that the purpose of dreams is to unburden our memory of the useless impressions of daytime [cf. pp. 105 f.] is plainly no longer tenable....}}</ref> and proposed that dreams preserve sleep by representing as fulfilled those wishes that otherwise would awaken the dreamer.<ref>Rycroft, Charles. ''A Critical Dictionary of Psychoanalysis''. London: Penguin Books, 1995, p. 41.</ref> Freud wrote that dreams "serve the purpose of prolonging sleep instead of waking up. ''Dreams are the'' GUARDIANS ''of sleep and not its disturbers.''"<ref>{{cite book |last=Freud |first=Sigmund |translator=James Strachey |editor=James Strachey |author-link=Sigmund Freud |date=1965 |title=The Interpretation of Dreams |page=253 |location=New York |publisher=Avon}}</ref>

[[File:Taras Shevchenko painting 0019.jpg|thumb|left|''Grandmother and Granddaughter Dream'' (1839 or 1840). [[Taras Shevchenko]]]]

A turning point in theorizing about dream function came in 1953, when [[Science (journal)|''Science'']] published the [[Eugene Aserinsky|Aserinsky]] and [[Nathaniel Kleitman|Kleitman]] paper<ref>{{cite journal |last1=Aserinsky |first1=Eugene |last2=Kleitman |first2=Nathaniel |author-link=Eugene Aserinsky |title=Regularly Occurring Periods of Eye Motility, and Concomitant Phenomena, during Sleep |journal=Science |year=1953 |volume=118 |issue=3062 |pages=273–274 |doi=10.1126/science.118.3062.273 |pmid=13089671 |bibcode=1953Sci...118..273A}}</ref> establishing [[Rapid eye movement sleep|REM sleep]] as a distinct phase of sleep and linking dreams to REM sleep.<ref>{{Citation |last=Smith |first=Robert C. |contribution=The Meaning of Dreams: A Current Warning Theory |editor-last1=Gackenbach |editor-first1=Jayne |editor-last2=Sheikh |editor-first2=Anees A. |title=Dream Images: A Call to Mental Arms |year=1991 |pages=127–146 |place=Amityville, NY |publisher=Baywood |isbn=0-89503-056-X}}</ref> Until and even after publication of the Solms 2000 paper that certified the separability of REM sleep and dream phenomena,<ref name="Solms1"/> 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:

[[Allan Hobson|Hobson's]] and [[Robert McCarley|McCarley's]] 1977 [[activation-synthesis hypothesis]], which proposed "a functional role for dreaming sleep in promoting some aspect of the learning process...."<ref>{{cite journal |last1=Hobson |first1=J. Allan |last2=McCarley |first2=Robert W. |title=The Brain as a Dream State Generator: An Activation-Synthesis Hypothesis of the Dream Process |journal=The American Journal of Psychiatry |date=December 1977 |volume=134 |issue=12 |pages=1335–1348 |doi=10.1176/ajp.134.12.1335 |pmid=21570 |quote=The dream process is thus seen as having its origin in sensorimotor systems, with little or no primary ideational, volitional, or emotional content. This concept is markedly different from that of the "dream thoughts" or wishes seen by Freud as the primary stimulus for the dream.}}</ref> In 2010 a Harvard study was published showing experimental evidence that dreams were correlated with improved learning.<ref>{{cite web |last1=Benjamin |first1=Victoria |title=Study Links Dreaming to Increased Memory Performance |url=https://www.thecrimson.com/article/2010/4/27/maze-wamsley-group-navigating/#:~:text=A%20recent%20study%20published%20last,nap%2C%20according%20to%20Erin%20J. |website=The Harvard Crimson |access-date=27 January 2022}}</ref>

[[Francis Crick|Crick's]] and Mitchison's 1983 "[[reverse learning]]" theory, which states that dreams are like the cleaning-up operations of computers when they are offline, removing (suppressing) parasitic nodes and other "junk" from the mind during sleep.<ref>{{cite journal |last1=Evans |first1=C. |last2=Newman |first2=E. |year=1964 |title=Dreaming: An analogy from computers |journal=New Scientist |volume=419 |pages=577–579}}</ref><ref>{{cite journal |doi=10.1038/304111a0 |last1=Crick |first1=F. |last2=Mitchison |first2=G. |year=1983 |title=The function of dream sleep |journal=Nature |volume=304 |issue=5922 |pages=111–114 |pmid=6866101 |bibcode=1983Natur.304..111C |s2cid=41500914}}</ref>

[[Ernest Hartmann|Hartmann's]] 1995 proposal that dreams serve a "quasi-therapeutic" function, enabling the dreamer to process trauma in a safe place.<ref>{{cite journal |last=Hartmann |first=Ernest |title=Making Connections in a Safe Place: Is Dreaming Psychotherapy? |journal=Dreaming |year=1995 |volume=5 |issue=4 |pages=213–228 |doi=10.1037/h0094437}}</ref>

[[Antti Revonsuo|Revonsuo's]] 2000 threat simulation hypothesis, whose premise is that during much of human evolution, physical and interpersonal threats were serious, giving reproductive advantage to those who survived them. Dreaming aided survival by replicating these threats and providing the dreamer with practice in dealing with them.<ref>{{cite journal |last=Revonsuo |first=A. |title=The reinterpretation of dreams: an evolutionary hypothesis of the function of dreaming |journal=Behavioral and Brain Sciences |year=2000 |volume=23 |issue=6 |pmid=11515147 |doi=10.1017/S0140525X00004015 |pages=877–901 |s2cid=145340071}}</ref> In 2015, Revonsuo proposed social simulation theory, which describes dreams as a simulation for training social  skills  and  bonds.<ref>{{Cite journal |last1=Revonsuo |first1=A. |last2=Tuominen |first2=J. |year=2015 |title=Avatars in the Machine: Dreaming as a Simulation of Social Reality |journal=Open MIND |pages=1–28 |doi=10.15502/9783958570375|isbn=9783958570375 }}</ref>

[[David Eagleman|Eagleman's]] and [[Don Vaughn|Vaughn's]] 2021 defensive activation theory, which says that, given the brain's [[neuroplasticity]], dreams evolved as a visual hallucinatory activity during sleep's extended periods of darkness, busying the occipital lobe and thereby protecting it from possible appropriation by other, non-vision, sense operations.<ref>{{cite journal |last1=Eagleman |first1=David M. |last2=Vaughn |first2=Don A. |title=The Defensive Activation Theory: REM Sleep as a Mechanism to Prevent Takeover of the Visual Cortex |journal=Frontiers in Neuroscience |date=May 2021 |volume=15 |page=632853 |doi=10.3389/fnins.2021.632853 |pmid=34093109 |pmc=8176926 |doi-access=free}}</ref>

[[Erik Hoel]] proposes, based on artificial neural networks, that dreams prevent overfitting to past experiences; that is, they enable the dreamer to learn from novel situations.<ref>{{cite news |title=Weird dreams train us for the unexpected, says new theory |url=https://www.theguardian.com/science/2021/may/14/weird-dreams-train-us-for-the-unexpected-says-new-theory |access-date=5 January 2023 |work=the Guardian |date=14 May 2021 |language=en}}</ref><ref>{{cite journal |last1=Hoel |first1=Erik |title=The overfitted brain: Dreams evolved to assist generalization |journal=Patterns |date=14 May 2021 |volume=2 |issue=5 |pages=100244 |doi=10.1016/j.patter.2021.100244 |pmid=34036289 |pmc=8134940 |language=en |issn=2666-3899|doi-access=free }}</ref>