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Does Dreaming Help Prepare Us for Life?

Dreamlike neural activity prepares mice to see even before their eyes open.

Key points

  • New research has shown that neural activity generated in the retina of the mouse eye prepares the visual system to see before eye opening occurs.
  • This activity can be said to resemble dreaming.
  • Newborn humans have significant cognitive abilities even before encountering real world sensory experiences.
  • Further research will be needed to better understand the neural mechanisms that prepare human infants for life in a complex world.
Photo by Silje Roseneng on Unsplash
closeup photo of brown hamster in glass cup
Source: Photo by Silje Roseneng on Unsplash

Every night we have four or more episodes of vivid dreaming. These occur during REM sleep when we are paralyzed and quite vulnerable. REM is when breathing pauses are most likely to occur in sleep apnea. A vulnerable state such this must have some important function to have been preserved during evolutionary history.

Many theories have been advanced for why we dream. Crick and Mitchison (1983) posited that REM serves the purpose of eliminating unhelpful interactions in networks of cells in the cerebral cortex through a process of reverse-learning. Crick was, of course, famous for helping determine the structure of DNA. The subjective experience of the dream could result from this process. The dream is a review of the day’s information while actively forgetting what isn’t needed. Work with neural networks has given some support to this model (see, e.g. Christos, 1996).

Other theories of dreaming have been proposed and include the activation-synthesis model that suggests that random thoughts, memories, and images are produced by underlying brain activity during REM and are formed into a coherent dream scenario upon awakening. Information processing theories see dreams as the biproduct of brain processes that result in memory consolidation. Dreaming may be also be involved in emotional processing or even help prepare us for real-world dangers by rehearsing possible coping strategies.

Klemm (2011) proposed that dreaming is a product of REM sleep that is activating and helps prepare the brain for the day’s activities by restoring consciousness after deep sleep. Anyone who has been awakened out of deep sleep in the middle of the night can attest to how hard it is to wake up and start thinking clearly. This contrasts with the typical feeling of being more awake and ready for the day when waking in the morning soon after a dream ends. “You could say REM is the brain’s way of ‘booting up’ its consciousness in the absence of an ‘external trigger’” (Klemm, 2011, p. 1).

A recent study lead by Michael Crair at Yale (Ge, Zhang, Gribizis, Hamodi, Sabino, & Crair, 2021) has raised the possibility that dreaming not only helps us get ready for the day, but also ready for life. They looked at neural circuits for vision in the mouse. These circuits develop before vision occurs and permit the mouse to see as soon as their eyes open. How does it happen that the visual system is self-organized to allow meaningful visual processing before there has been any exposure to visual stimuli? This occurs through the generation of propagating waves that arise spontaneously in the retinas of the animals’ eyes and allows the visual system to begin to develop and function. Ge et al (2021) looked at the possibility that this activity could aid in the development of visual abilities such as direction selectivity.

They used a complex methodology to study the development of visual abilities in the newborn mouse. They found that spontaneous retinal activity was structured so as to simulate forward motion in space, which prepares the mouse for perceiving this movement upon eye opening and contributes to the development of higher-order visual function. This occurs before eye opening and before the mouse has experienced any visual input. Dr. Crair pointed out that “(t)his early dream-like activity makes evolutionary sense because it allows a mouse to anticipate what it will experience after opening its eyes, and be prepared to respond immediately to environmental threats,” (Hathaway, p. 3). He further suggested that something like this is occurring in humans to allow visual abilities, like detecting the movement of a finger across the visual field, to be present at birth.

Indeed, human newborns have been shown to have significant cognitive abilities (Streri, de Hevia, Izard, & Coubart, 2013). They are able to use all of the senses to process social and physical information to distinguish between faces and other objects and can remember and recognize them. They can compare different sensory inputs and match them so as to learn about the environment. Streri et al. (2013), argued that these abilities are the foundations of human cognition. They are present at birth and are clearly not the result of the pre-birth environment, which does not match the complex world into which the infant is born. “Since newborns must enter in contact with a complex, multidimensional world, they ought to possess some mechanisms that allow them to immediately adapt to that environment. Even though at birth these mechanisms are still weak, clumsy, and primitive, it is thanks to them that newborns develop and adapt directly to their environment” (Streri et al., 2013, p. 164).

Patterns of activity that can be characterized as sleep emerge during the third trimester of pregnancy and the quality of that sleep may have implications for later development (Van den Bergh & Mulder, 2012). The sleep of newborn babies is different from that of children and adults. Adults have 4 clear stages of sleep known as N1, N2, N3, and REM. REM is so distinctive that the other stages are known as “non-REM”. In contrast, newborn infants in the first three months of life spend about 18 hours out of every 24 asleep. Their sleep is broken into shorter periods rather than the 16 hours of wakefulness and 8 hours of sleep we associate with adult sleep. Adults usually spend about 25% of the night in REM sleep. About half of sleep time for the infant is spent in “quiet sleep”, which is similar to NREM sleep, and the other half in “active sleep”, that is similar to REM sleep.

Scientists have not fully worked out how the ability of infants to rapidly interact with and understand their environments develops. The study by Ge et al (2021) was done in mice and revealed one way in which the visual system of an animal prepares for the challenges of life. This mechanism may or may not be one that has a role in human development but does illuminate possible future avenues of research and suggests yet another role for dreaming in the mental life of creatures great and small.

This vector image was created with Inkscape by Klem, and then manually edited by Mnmazur.. Licensed under Public Domain via Wikimedia Commons
"Yin and Yang" by Klem
Source: This vector image was created with Inkscape by Klem, and then manually edited by Mnmazur.. Licensed under Public Domain via Wikimedia Commons

References

Christos, G.A. (1996). Investigation of the Crick-Mitchison reverse-learning dream sleep hypothesis in a dynamical setting, Neural Networks, 9(3), 427-434, ISSN 0893-6080,

https://doi.org/10.1016/0893-6080(95)00072-0.

Crick, F., Mitchison, G. (1983). The function of dream sleep. Nature, 304, p. 111–114, https://doi.org/10.1038/304111a0

Ge, X., Zhang, K., Gribizis, A., Hamodi, A. S., Sabino, A.M., Crair, M. C. (2021). Retinal waves prime visual motion detection by simulating future optic flow. Science, 373(6553), DOI: 10.1126/science.abd0830

Hathaway, B. (2021). Eyes wide shut: How newborn mammals dream the world they’re entering. Yale News, July 22, 2021, p. 3.

Klemm, W. R. (2011).Why Does Rem Sleep Occur? A Wake-Up Hypothesis. Frontiers in Systems Neuroscience, 5, p. 1 -12, URL=https://www.frontiersin.org/article/10.3389/fnsys.2011.00073 DOI=10.3389/fnsys.2011.00073, ISSN=1662-5137

Streri, A., de Hevia, M. D., Izard, V., & Coubart, A. (2013). What do We Know about Neonatal Cognition?. Behavioral sciences (Basel, Switzerland), 3(1), 154–169. https://doi.org/10.3390/bs3010154

Van den Bergh, B.R.H. & Mulder, E.J.H. (2012). Fetal sleep organization: A biological precursor of self-regulation in childhood and adolescence?, Biological Psychology,

89(3), p. 584-590, ISSN 0301-0511, https://doi.org/10.1016/j.biopsycho.2012.01.003.

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