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Sleep

Why Do We Dream?

Dreams are caused by neural processes in sleep but may not have any function.

Key points

  • Many theorists from Freud to current neuroscientists have tried to explain the function of dreams.
  • Increased understanding of the brain suggests that dreams are byproducts of neural processes with no special function.
  • These neural theories of dreams are incomplete without a complementary theory of consciousness.

Dreams are conscious experiences that occur during sleep, and today there are many alternatives to Freud’s theory that dreams are wish fulfillments.

Dreams Are Divine Communications

Many cultures, from the ancient Greeks to Indigenous American groups such as the Iroquois, have assigned spiritual significance to dreams. We dream because the gods are speaking to us or because we can transcend the limitations of our bodies and explore the future. The problem with these views is lack of evidence for gods and their communications. Most dreams are about mundane activities such as work and family and should be open to nonspiritual explanations.

Dreams Are Wish Fulfilments

Sigmund Freud thought that his theory of dreams was his most valuable discovery, important for giving a scientific explanation of why people dream and also for suggesting dream analysis as a useful part of psychotherapy. Dreams are symptoms of unconscious wishes that may be at the root of psychological problems. Freud struggled to explain why most dreams are disagreeable and why many patients do not benefit from his psychoanalytic techniques. Another puzzle for the Freudian approach is why most dreams are not remembered.

Dreams Are Byproducts of Neural Processing

J. Allan Hobson was a Harvard psychiatrist who pioneered the first serious scientific alternative to Freud’s ideas about dreams. He proposed that dreams are brain processes resulting from neural activations that occur during rapid-eye-movement (REM) sleep, without the usual sensory and motor inputs that are blocked by the thalamus. The brain tries to make sense of these activations using its memories, but the results are delusional and of little psychological significance. Many of Hobson’s proposed neural mechanisms turned out to be wrong—for example, through the finding that dreams also occur in non-REM sleep.

G. William Domhoff agrees with Hobson that dreams have no adaptive biological function but offers a different neural explanation. The default network connects important regions in different parts of the brain and operates in the absence of sensory inputs. Domhoff thinks that during sleep the default network generates imaginations and simulations that produce dreams. Domhoff takes seriously the thousands of reports of dreams that have been accumulated in dream banks and sees dreaming as continuous with everyday cognition. However, he does not have a theory of consciousness that could explain why the activity of the default network generates experiences such as visual imaginings and feelings of anxiety.

Dreams Are Emotional Regulation

Not all neuroscientists think that dreams are useless. Matthew Walker describes many valuable biological functions of sleep, including restoring the brain, metabolism, immune system, and cardiovascular system. He also thinks that the neural processes of dreaming bring important benefits for regulating the emotions and creativity. Sleep is known to be important for consolidating daytime memories into permanent storage, and emotion-related areas of the brain are also active during this process. Walker thinks that REM sleep helps us not only to remember emotionally important events but also to dissolve painful emotional charges. Moreover, the unusual associations that occur in dreaming can help to generate creative new ideas. However, Walker does not show that emotional regulation and creativity are the reasons that organisms evolved brains that dream. Perhaps emotion regulation and creativity are just useful side effects of dreaming, not its biological purpose.

Dreams Are Cognitive Explorations

An alternative function of dreams is proposed by neuroscientists Antonio Zadra and Robert Stickgold. They propose a model of dream function called NEXTUP for “network exploration to understand possibilities.” Dreaming serves to extract new knowledge from existing memories by discovering and strengthening existing associations. When we dream about being chased, having sex, or school examinations, we are preparing ourselves to deal with a changing world. But whether dreams are useful in this way is debatable given that most of them are never remembered, many of them are bizarrely unrealistic, and the majority of dreams are unpleasant.

Dreams Are Predictive Processing

In his later years, J. Allan Hobson tied his activation-synthesis view of dreaming to the increasingly popular view that the brain functions primarily as a prediction engine operating by Bayesian inference. In a previous post, I argued that the brain has many important functions besides prediction and that there is no reason to think that it uses probabilistic calculations to carry out these functions. Like the NEXTUP model, Hobson came to see dreams not as random but as having useful benefits in making predictions, which is problematic given the bizarre and forgettable character of most dreams. Many people dream of flying and falling, two activities that most of us do rarely.

What Causes Dreams?

Dreams result from unusual patterns of neural firing that occur during sleep. In order to restore the body and brain, sleep shuts down the body’s sensory inputs and motor activities that normally constrain neural firings. Aberrant neural signals may also result as side effects of memory consolidation and the replenishment of neurotransmitters that were depleted during the brain’s daily activities.

The brain is not just a prediction engine but also a coherence engine that tries to make sense of what is going on, internally and externally. For example, the brain stem interacts with sensory inputs and other brain areas to produce physical balance that enables us to remain upright while moving around the world. Sometimes, however, balance goes wrong when defective signals from the inner ear or eyes or brain damage generate misinterpretations that lead to vertigo, nausea, or falls. Similarly, during dreaming the brain generates false interpretations that we are having perceptions, emotions, and thoughts about reality.

I, therefore, suspect that dreams result from aberrant signals and more-or-less coherent interpretations that depend on many brain areas, not just the default network. Most interpretations carried out by patterns of neural firing are unconscious, but some of them emerge into conscious experiences that are remembered after waking. Dreams are side effects of neural mechanisms for sleep and consciousness, and no special significance should be attributed to them.

References

Domhoff, G. W. (2018). The emergence of dreaming: Mind-wandering, embodied simulation, and the default network. Oxford: Oxford University Press.

Domhoff, G. W. (2022). The neurocognitive theory of dreaming: The where, how, when, what, and why of wreams. Cambridge, MA: MIT Press.

Freud, S. (1938). The interpretation of dreams (A. A. Brill, Trans.). New York, Modern Library.

Hobson, J. A. (1988). The dreaming brain. New York: Basic Books.

Hobson, J. A., Hong, C. C.-H., & Friston, K. J. (2014). Virtual reality and consciousness inference in dreaming. Frontiers in Psychology, 5, 1133.

Thagard, P. (2022). Balance: How it works and what it means. New York: Columbia University Press.

Walker, M. (2017). Why we sleep: Unlocking the power of sleep and dreams. New York: Simon and Schuster.

Zadra, A., & Stickgold, R. (2022). When brains dream: Understanding the science and mystery of our dreaming minds. New York: W. W. Norton.

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