Why do we dream?
Three answers to the question, in the order they arrived: a book from 1900, a sleep laboratory in 1953, and brain and memory studies since.
Answer to the question
Why do we dream?
Researchers do not agree on one reason. Sigmund Freud's 1900 book treated dreams as disguised messages, a 1977 account described them as the forebrain making sense of brainstem activity, and a 2010 study linked dreaming about a task to better memory afterwards. Brain recordings now tie dream experience to one back-of-brain region.
Key takeaways
- Peter Watson's The Modern Mind treats Sigmund Freud's The Interpretation of Dreams, dated 1900, as the opening idea of the century, with dreams read as disguised expressions of urges that sleep lets surface.
- In 1953 Aserinsky and Kleitman found that 20 of 27 awakenings during periods of rapid eye movement produced detailed dream reports, while 19 of 23 awakenings after long quiet stretches produced no recall.
- Hobson and McCarley proposed in 1977 that brainstem activation switches on the forebrain, which synthesises the result into a dream.
- In a 2010 nap study of 99 students, four who mentioned a virtual maze in their dreams improved about ten times more at retest than nappers who did not.
- A 2017 study linked dream reports to lower slow activity in a back-of-brain region in rapid-eye-movement and other sleep stages.
This article is general information about research on dreaming. It is not medical advice, and nothing in it is a reason to change any treatment or to stop seeking care. Speak to a GP or another clinician about your own health. Medical review: Reja Batool.
Why do we dream? Dreaming has been explained in three main ways since the twentieth century began: as disguised messages, as a by-product of brain activity, and as part of how memory is kept. Peter Watson begins The Modern Mind with the first of them. Sigmund Freud's The Interpretation of Dreams was printed at the very end of the nineteenth century and dated for the new one, which makes it, in Watson's account, the opening idea of an era that went on to study the mind in laboratories. The three answers arrived in order, and each speaks to a different question about the same nightly event.
How a Vienna book on dreams opened a new century
Freud knew a book on dreams carried a risk, because reading dreams for meaning was an ancient practice and the German title could be taken for a book of that older kind. His claim was narrower and new. Sleep, he argued, relaxes the part of the mind that normally keeps urges in check, so those urges surface in the dream in disguise, and a person's account of a dream can be worked back towards what it hides.
Interest grew through people. Within a few years a Viennese physician, Wilhelm Stekel, read a review of the book and called on Freud to discuss it, then asked to be analysed himself, and a year later began to practise psychoanalysis. Watson also traces a route into art. André Breton first met the psychoanalysis of dreams while serving in a wartime hospital, and the surrealist movement later took dreams and the unconscious as raw material. By then the question of why we dream belonged to writers, painters and physicians alike.
Watson describes a modest start, with fewer than half of the first printing sold in the first two years. The lasting effect of that book on this question was to make a dream something with a cause that could be examined. It also supplied a first answer to why we dream: the dream does work for the sleeper by letting a hidden wish speak safely. Later researchers took the question forward by other routes, and they kept it in the form Freud posed it.
Rapid eye movements, the forebrain and a physical explanation
A different kind of answer needed a different kind of tool. In a sleep laboratory a dream could be approached by the clock: when does a sleeper dream, and what is the body doing at that moment?
In 1953 Eugene Aserinsky and Nathaniel Kleitman recorded eye movements and brain waves in 20 adult volunteers across a series of experiments. Periods of rapid, jerky eye movement began about three hours after sleep onset, lasted from 6 to 53 minutes with an average of 20, and returned through the night, closer together towards morning. When sleepers were woken during those periods, 20 of 27 interviews produced a detailed dream report. When they were woken after long quiet stretches, 19 of 23 reported no recall at all. Dreaming now had a physical signature that could be measured and timed.
In 1977 J. Allan Hobson and Robert McCarley proposed what the brain might be doing during those periods. In their activation-synthesis hypothesis, brainstem mechanisms switch on the forebrain at regular intervals, bursts of activity in sensory and motor circuits shape the imagery, and the forebrain does its usual job of making a whole from what reaches it by comparing it with stored memory. On this account a dream begins in physiology and the story is the forebrain's best synthesis of it.
That is a different kind of answer from Freud's. It explains how a dream is produced and says less about what any one dream means, so the two accounts were never really competing for the same ground. The laboratory answer also moved the question of why we dream from the consulting room to the clock, the electrode and the sleeping brain, where the next two studies took it.
Dreaming today: tied to memory, and to one brain region
| Year | Researchers | Question asked | Reported answer |
|---|---|---|---|
| 1900 | Sigmund Freud | What does a dream mean? | Sleep loosens the guard on urges, which surface in disguise. |
| 1953 | Aserinsky and Kleitman | When does dreaming happen? | Dream reports followed periods of rapid eye movement. |
| 1977 | Hobson and McCarley | How is a dream produced? | Brainstem activation, synthesised by the forebrain. |
| 2010 | Wamsley and colleagues | Does dreaming relate to memory? | Dreaming of a learned task went with larger gains after a nap. |
| 2017 | Siclari and colleagues | Where in the brain? | A back-of-brain region tracks dream experience in several sleep stages. |
Erin Wamsley, Robert Stickgold and colleagues asked whether dreaming connects to memory. 99 students learned a three-dimensional virtual maze, and then either napped or stayed awake before a retest five hours after training. Nappers were kept to non-rapid-eye-movement sleep, woken at the first signs of the rapid-eye-movement stage, and asked what had been on their minds. Four nappers who mentioned the maze in their dream reports improved about ten times more at retest than nappers who did not, while thoughts about the maze while awake did not predict improvement. Four people is a small group, so the authors treat the result as an association and not a cause.
The finding sits alongside work on how a memory is stored and reworked after learning, which is the subject of What is an engram, and on replaying a task in the mind, covered in Does mental rehearsal improve performance.
Francesca Siclari, Giulio Tononi and colleagues asked where in the brain a dream is found. They woke sleepers repeatedly through the night while recording brain activity with 256 electrodes. Across 32 volunteers woken a few times each and 7 trained reporters woken many times, a reported dream went with a local drop in slow, low-frequency activity in a region at the back of the cortex, in both rapid-eye-movement sleep and the other stages. Faster activity in the same region tracked the specific content of a dream. In a third group of 7 volunteers, watching that region in real time predicted with good accuracy whether someone was dreaming in non-rapid-eye-movement sleep.
That result extends the 1953 picture. Dream reports cluster in rapid-eye-movement sleep but are not confined to it, and one region of the brain follows them across stages. A night of dreaming can be read as a message, as brain activation, or as recent learning being handled, and the reading that fits depends on the question put to it.
Common questions
Why do we dream?
Researchers do not agree on one reason. Freud's 1900 book treated dreams as disguised messages, a 1977 account described them as the forebrain making sense of brainstem activity, and a 2010 study linked dreaming of a task to better memory afterwards.
When does dreaming happen during sleep?
In 1953 Aserinsky and Kleitman found that most detailed dream reports followed periods of rapid eye movement. Later recordings found dream reports in other sleep stages too.
Does dreaming about a task help memory?
One nap study found that four students who dreamed about a maze improved much more than those who did not. The group was small, so the result is an association.
Can brain activity show that someone is dreaming?
A 2017 study tied dream reports to lower slow activity in a back-of-brain region and predicted dreaming in real time during one sleep stage.
Sources
Watson, P. The Modern Mind: An Intellectual History of the 20th Century. Seed book; vault hub Books/The Modern Mind.
Aserinsky, E., & Kleitman, N. (1953). Regularly occurring periods of eye motility, and concomitant phenomena, during sleep. Science, 118(3062), 273-274. doi:10.1126/science.118.3062.273 https://doi.org/10.1126/science.118.3062.273
Hobson, J. A., & McCarley, R. W. (1977). The brain as a dream state generator: An activation-synthesis hypothesis of the dream process. American Journal of Psychiatry, 134(12), 1335-1348. doi:10.1176/ajp.134.12.1335 https://doi.org/10.1176/ajp.134.12.1335
Wamsley, E. J., Tucker, M., Payne, J. D., Benavides, J. A., & Stickgold, R. (2010). Dreaming of a learning task is associated with enhanced sleep-dependent memory consolidation. Current Biology, 20(9), 850-855. doi:10.1016/j.cub.2010.03.027 https://doi.org/10.1016/j.cub.2010.03.027
Siclari, F., Baird, B., Perogamvros, L., Bernardi, G., LaRocque, J. J., Riedner, B. A., Boly, M., Postle, B. R., & Tononi, G. (2017). The neural correlates of dreaming. Nature Neuroscience, 20(6), 872-878. doi:10.1038/nn.4545 https://doi.org/10.1038/nn.4545