@Article{FranklinZyphur2005,
author = {Franklin, Michael S. and Zyphur, Michael J.},
title = {The Role of Dreams in the Evolution of the Human Mind},
journal = {Evolutionary Psychology},
year = {2005},
volume = {3},
pages = {59--78}
}
Dreaming serves as a kind of rehearsal or memory-enhancing function. (p. 62)
This rehearsal function would have been a target for selection.
The activation-synthesis theory (Hobson & McCarley, 1977) is insufficient to account for the content of dreams. (p. 64)
The ability to dream has a heritable component. (p. 65)
The physiological processes associated with REM sleep are also likely genetically determined. (p. 66)
Dreams are used as a threat-rehearsal mechanism. (p. 66)
“We propose that the fitness-enhancing benefits of dreaming is not restricted to threat rehearsal, and the evolution of other higher-order cognitive faculties has been strongly influenced by a dreaming mechanism.” (p. 66)
Noise propagated from the brainstem may account for the variability of dream content, and may facilitate the simulation of a broad range of scenarios. (p. 67)
Sleeping and waking consciousness appear to use similar cognitive and neural processes; performing tasks in the dream state could improve performance in waking life. (p. 68)
Experiences in the dream-state are perceived as real, despite the often bizarre qualities of dreams. (p. 68)
Threatening or trying scenarios could be played out in dreams without being hindered by the need for total realism. (p. 68)
Dreaming may also serve as a rehearsal mechanism for social cognition, as well as aid in the interpretation of social cues etc. (p. 69)
Dreaming may form a critical part of mental development in general, explaining why babies spend such a long time in REM sleep. (p. 72)
Disturbed sleep patterns in autistic children may explain some associated mental deficiencies. (p. 73)
The original article can be found at http://www.epjournal.net/filestore/ep035978.pdf
Dreams are a state of consciousness that have been selected by evolution for their adaptive value. (p. 60)
All people dream (with the exception of some neuropsychological patients), but the content of peoples dreams can vary greatly. The variable and subjective nature of dreams should not prohibit a scientific analysis of the role of dreams. (p. 60)
Most vivid dreams occur during REM sleep. (p. 61)
REM sleep is characterized by (p. 61):
High brain activity; alpha and beta waves.
Paralysed muscle activity
Rapid eye movements
Neurological damage can prevent muscle paralysis, and can lead to people acting out their dreams. (p. 62)
Rats who have spent time running mazes during the day show activation in the same hippocampal place cells during REM sleep that were active while awake. Dreaming may thus serve as a rehearsal mechanism of some kind. (p. 62)
Animals likely experience a kind of dream-state similar to our own as evidenced by lesion studies where muscle paralysis is turned off, and animals act out their dreams. (p. 62)
The activation-synthesis hypothesis (Hobson & McCarley, 1977) posits that dreaming is the result of random neural activity propagated by the pons, and interpreted by cortical areas. (p. 63)
The activation-synthesis hypothesis does not account for the non-random content of dreams as evidenced by the fact that many dreams exhibit a coherent story-line. The pons is also not necessary for dreams to occur, and the forebrain region plays a crucial role in the generation of dreams, contrary to the activation-synthesis hypothesis. (p. 64)
The brain spends a lot of time visualizing and rehearsing 'unreal' data. Similar neural and cognitive mechanisms are activated when processing either real or unreal data, and imagining various tasks can improve performance in real life. (p. 64, 65)
Dreaming appears to be a virtual-simulation mechanism used to rehearse important behaviours without actually performing them. (p. 65)
An environment-simulation mechanism used to improve real-life performance would be advantageous to an individual's survival, and would thus be a target of natural selection. (p. 65)
Dreaming may act as a threat-rehearsal device. (p. 65)
Given that REM sleep is only observed in placental and marsupial animals, the ability to dream seems to be genetically heritable. The physiological processes behind dreaming like muscle paralysis etc. are also likely genetically determined. (p. 65)
Around 80% of dreams contain negative content, giving credence to the idea that dreams are utilized to rehearse threatening scenarios. According to the activation-synthesis hypothesis, dream content should be random. (p. 66)
Dreaming is not restricted to just threat rehearsal, it likely plays a role in other important cognitive functions. (p. 66)
Random neural activity emanating from the pons during REM sleep may be beneficial to dreaming. It is hypothesized that the noise in the system helps the frontal areas construct different scenarios, allowing for an increased range of possible simulations. (p. 67)
Evidence from lucid dream studies reveals that tasks performed in dreams activates the same brain regions as in waking cognition. The brain does not seem to differentiate between dream consciousness and waking consciousness. (p. 67, 68)
Dreams with even the most bizarre content are perceived as real. This would prove advantageous, since simulations would not need to be entirely realistic in order to practice important cognitive capacities. (p. 68)
Frontal regions responsible for critical thinking and planning etc. are inhibited during dreaming to make the experience seem more real. The inability to think about goals other than the task at hand is referred to as situated cognition. (p. 68)
Brain regions involved in social cognition are consistently activated during REM sleep and many dreams contain social content. This leads to the idea that dreaming may serve to develop social skills and help interpret social cues. (p. 69)
Children's dreams are more likely to contain family members and close friends than adults'; they need to understand social cognition more crucially than adults. (p. 69)
Dreams do not have to be 100% realistic in order for them to be useful for developing basic cognitive skills. (p. 70)
Dreaming provides a rich virtual environment to explore and develop skills. This may explain why babies spend about 8 hours in REM sleep per day; they are developing various mental capacities through virtual simulation. (p. 71)
The authors predict a healthy sleep schedule in infants will lead to optimal development, whereas a disrupted sleep schedule will lead to mental deficiencies. Disturbed sleep patterns in autistic children may account for some associated mental deficits. (p. 72)
Lucid dreamers are an exception to situated cognition in dreams, they are aware that they are dreaming and can consciously control their actions. (p. 72, 73)
While most people do not remember the content of their dreams, conscious recall of events is not needed to develop cognitive skills. (p. 73)
In sum, dreaming is a cognitive trait that has provided a survival advantage for our species as it allows the simulation and rehearsal of various important situations and behaviours.