Why do we dream?

Dreaming is a universal feature of human experience, but there is no convincing explanation as to why we should experience dreams during sleep. Why do we have vivid, intense, and eventful experiences while we are completely unaware of the world that physically surrounds us? Couldn’t we just as well pass the night completely? Do our dreams have colours? We must understand the function and the concept of dreaming.

Well, the function of dreaming seems to be a persistent mystery, although numerous suggestions have been put forward about the possible functions it might serve. The leading nuerocognitive theories, however, seem to have given up the hope of identifying any useful function for dreaming at all. They cannot provide us with an answer to the question “Why do we dream?” Instead, they seem to imply that we dream for no particular reason at all: Dreaming is biologically epiphenomenal. Dream consciousness is viewed as some sort of random noise generated by the sleeping brain as it fulfils various neurophysiological functions during REM (rapid eye movement) sleep.

Although Freud (1900) proposed that dreaming and, specifically, the meaningful content of dreams are related to mental functioning, the tenuous and misunderstood nature of dreams has made the proposition of empirically providing support for, or falsifying, this claim is very problematic. The inability to study the effects of dreams on mental functioning has forced many researchers to view dreams as the result of random neural activity (e.g., the activation-synthesis hypothesis; Hobson and McCarley, 1977). If postulation regarding the random nature of dreams are indeed true, then it becomes challenging to construct a theory of how the phenomenology of the dream state could serve a functional role and be better understood through an evolutionary analysis.


How do dreams work?

Your brain ‘flushes out’ emotional arousal by creating a dream of a scenario that parallels the real-life experience – a metaphor. So, the work colleague from above might be symbolised by a monster and your anger would be allowed expression as you attacked the dream creature.

If you ruminate angrily over the same issue the next day then you may well have a repetitive dream as the brain solves the same problem in the same way.


The subjective nature of dreams

The nature of the dream-state is highly subjective and a truly personal experience making the scientific analysis of dreaming somewhat prohibitive. Dreams often contain material that is nonsensical and challenging to interpret rationally, making the characterisation of dreams from an objective point of view a perplexing task. While we all dream (though see Solms, 1997, for an example of neuropsychological patients who don’t dream), there is incredible variability in the subjective dream experience (Hall and Van de Castle, 1966; Spadafora and Hunt, 1990). Some people rarely remember their dreams and erroneously conclude that they do not dream at all (a condition discussed by Freud, 1900), while others experience vivid dreams with rick visual imagery and emotional content. Sometimes, the story-lines that make up people’s dreams follow a tight narrative and have a relatively smooth transition from scene to science, while at other times dreams appear as illogical and haphazard associations lacking a coherent sense of flow.

Some people have full control of their dreams, exerting conscious control over the supposedly random events which typify dreaming (Laberge, Levitan, Dement, 1986), while others are mere bystanders watching the events unfold without any sense of agency approximating waking volition.

REM sleep and dreaming

One of the first and most important findings in the history of research on dreams and dreaming is that which related the phenomenon of dreaming and the physiological occurrence of rapid eye movement (REM) sleep (Dement and Kleitman, 1957). While dreaming refers to “the subjective conscious experience that we have during sleep” (Revonsuo, 2000, p. 878), REM sleep is a physiologically-define stage of sleep. It has been established that dreaming does occur during REM sleep through the collection of dream reports from subjects awoken from REM sleep, though the same is true for non-REM sleep (NREM; Hobson, 1988). Rather than being a static process, sleep contains a number of discrete states defined by various physiological measures (Rechtschaffen and Kales, 1968).

The use of electroencephalography (EEG), electro-oculography (EOG), and electromyography (EMG) has proven useful in distinguishing between arousal states during sleep, by measuring brain activity, eye movements, and muscle activity, respectively. As we sleep, our brain passes through various stages in a cyclical manner. Some of these stages are characterised by slow brain activity and other stages occur in which the electrical activity of the brain mimics the waking brain, and can even considered hyperactivated. This specific, hyperactive stage of sleep is known as REM sleep and has three characteristics that define it:

  1. The brain is more active that while in other stages and the EEG consists of alpha and beta activity, similar to waking,
  2. Muscle activity is actively inhibited within the central nervous system in order to promote paralysis, and,
  3. Eye-movements occur during REM sleep because the muscle paralysis does not extend to the eye muscles.

Theories of dreaming

The theory of dreaming most generally accepted, which offers and explanation of dreaming based on the physiology of REM sleep, is Hobson and McCarly’s (1977) activation-synthesis hypothesis. According to this hypothesis, dreams are the result of the forebrain responding to random activity initiated at the brainstem. This is demonstrated by the PGO waves that occur during REM sleep. Specifically, PGO refers to the pons, where the activity originates; the lateral geniculate nucleus of the thalamus, which is the area through which sensory information passes; and occipital areas, where visual information is processed. According to Hobson and McCarly (1977), this random activity, or noise, emanating from the pons, passes through similar sensory-relay stations as information from the environment, and is interpreted in a way that leads to phenomenology of dreaming. Overall, this theory has received general support for some time because it fits well with physiological data and its explanation of dreaming appeals to a majority of people’s’ dream experiences, again, being somewhat haphazard and random. This theory posits that the bizarre nature of dreams in attributed to certain parts of the brain attempting to piece together a story out of what is essentially random. Personally, I believe in this theory.

The activation-synthesis theory does make intuitive sense, based not only on how we generally remember and report information from dreams, but also on how difficult it is to piece together memories of a dream upon waking. Neuropsychological evidence points towards our tendency to confabulate stories that we believe to be true in order to fit together disparate pieces of information (Gazzaniga, 198). If true, however, the supposedly random information that leads to dreaming would weaken the evolutionary analysis presented here. If there is not bias towards a particular type of information processed during REM sleep, then it becomes hard to imagine how dreaming could be selected for in an evolutionary context. Specifically if there is no rhyme or reason with regards to the content that makes up dreams, it becomes difficult to understand the advantage of experiencing such a haphazardly concocted virtual dream environment.

Additional neuropsychological evidence reveals that the brainstem mechanism, which is a key ingredient in activation-synthesis theory, is not necessary for dreams to occur. Rather, work by Solms (1997, 2000) points towards the forebrain region as being crucial in the generation of dreams. If there is reason to believe that dreaming is not just the random processing of information, but instead there is some pattern to the types of themes present in dreams and the possibility that dreams can consist of cohesive story-lines, then it seems logical to investigate why these patterns exist and what purpose they serve.

Do we dream in colour?

You probably think you dream in colour. If my anecdotal impressions and previous research are trustworthy, most contemporary English speakers do (Schwitzgebel, 2003). Apparently, so did Aristotle (in Gallop, 1996), Descartes (1649/1985), Freud (1900/1931), and everyone else I have been able to find who wrote on the topic prior to the 20th century. In the middle of the 20th century, however, research psychologists and the general public in the United States thought they dreamed primarily in black and white (e.g., Middleton, 1942; Hall, 1951; de Martino, 1953; see Schwitzgebel, 2002 for a review).

We think it highly unlikely that people’s dreams actually changed from colour to black and white and back again. For one thing, the rate of colour term use in mid-century dream reports appears to be virtually identical to the rate of colour term use in late-century dream reports (see Schwitzgebel, 2002, note 4, for details).


references & Resources

  1. Braun, A. R., Balkin, T. J., Wesensten, N.J., Gwadry, F., Carson, R.E., Varga, M., Baldwin, P., Belenky, G., & Herscovitch, P. (1998, January 2). Dissociated pattern of activity in visual cortices and their projections during human rapid eye movement sleep. Science, 279, 91-95.
  2. Schwitzgebel, E. (2002). Why did we think we dreamed in black and white? Studies in History and Philosophy of Science, 33, 649-660.
  3. Schwitzgebel, E. (2003). Do people still report dreaming in black and white? An attempt to replicate a questionnaire from 1942. Perceptual and Motor Skills, 96, 25-29.
  4. Wehrle, R., Czisch, M., Kaufmann, C., Wetter, T. C., Holsboer, F., Auer, D. P., Pollmächer, T. (2005). Rapid eye movement-related brain activation in human sleep: A functional magnetic resonance imaging study. Neuroreport, 16, 853-857.
  5. Encyclopedia of Sleep and Dreaming. Edited by Mary A. Carskadon. Macmillan 1993.
  6. Narcolepsy. Jerome M. Siegel in Scientific American, Vol. 282, No. 1, pages 76-81; January 2000.
  7. Centre for Sleep Research at U.C.L.A.: www.npi.ucla.edu/sleepresearch
  8. Hobson, J. A., and McCarley, R. W. (1977). The brain as a dream state generator: An activation synthesis hypothesis of the dream process. American Journal of Psychiatry, 134: 1335-1348.
  9. Hobson, J. A., Pace-Schott, E. and Stickgold, R. (2000). Dreaming and the brain: Toward a cognitive neuroscience of conscience states. Behavioral and Brain Sciences, 23: 783-842.
  10. Solms, M. (1997). The Neuropsychology of Dreams: A Clinico-Anatomical Study. Mahwah, New Jersey: Lawrence Erlbaum.
  11. Solms M. (2000). Dreaming and REM sleep are controlled by different brain mechanisms. Behavioral Brain Science, 23: 843-50.
  12. Dement, W. C. and Kleitman, N. (1957). The relation of eye movements during sleep to dream activity: An objective method for the study of dreaming. Journal of Experimental Psychology, 53: 339-346.
  13. Devinsky, O., Morrell, M. J., and Vogt, B. A. (1995). Contributions of anterior cingulate cortex to behavior. Brain, 118: 279-306.
  14. Rechtschaffen, A. and Kales, A. (1968). A Manual of Standardized Terminology, Techniques and Scoring Systems for Sleep Stages of Human Subjects. Los Angeles, CA: UCLA Brain Information Service/Brain Research Institute.
  15. Image via The Technological Citizen. Retrieved from:
  16. Slider image via squishgames.com. Retrieved from:

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: