What is the Function of Dreaming?

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Biology 202
2004 Second Web Paper
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What is the Function of Dreaming?

Ghazal Zekavat

Plutarch, a Greek biographer and author (circa 46 - 125 AD) (1) is credited to having said, "all men whilst they are awake are in one common world: but each of them, when he is asleep, is in a world of his own." (2) Plutarch is essentially speaking of the phenomenon of dreaming. The idea that the mind creates its own world while asleep is quite thought-provoking. What is it about sleep that takes us to another world? Where does this other world come from? What purpose, if any does dreaming serve? One school of thought suggests that dreaming is a product of random electrical activity that the cortex tries to interpret (3) that really serves no purpose (4), while another insists that the purpose of dreaming has come about as a byproduct of evolution (4). Which story is right?—or rather, less wrong?

It will first prove helpful to understand the process of sleep. Sleep is a dynamic activity controlled by neurotransmitters acting on different neurons in the brain. We sleep in cycles of 5 stages: 1, 2, 3, 4 and Rapid Eye Movement (REM). Light sleep occurs during stage 1, where a person can easily drift in and out of sleep. People waking up from stage 1 sleep often experience flashbacks of fragmented images, and/or sudden muscle contractions called "hypnic myoclonia" which usually precede the sensation of just starting to fall. In stage 2 sleep, brain waves slow down and eye movement stops. Stage 3 and 4 are collectively called "deep sleep" as it is usually very difficult to wake someone up in either stage. During stage 3, delta waves (very slow brain waves) appear, interspersed with smaller faster waves which leave altogether during stage 4. During the REM stage, we experience shallow, irregular and more rapid breathing, our eyes move rapidly in various directions, our limb muscles become temporarily paralyzed, our heart rate and blood pressure increase, and males develop penile erections. When someone wakes up during the REM stage, they often describe outlandish, unfounded tales – those which we call: dreams. (5)

REM sleep begins with signals being sent from the pons to the thalamus which then relays the signals to the cerebral cortex. The cerebral cortex is the part of the brain used for learning, thinking, and organizing information, so this is an important point. Infants tend to spend much more time in the REM stage than adults, possibly for this very reason, that the REM stage stimulates the brain regions used in learning. (5)

Many scientists believe that the random electric activity is just that – random. They then assert that the cortex creates stories in order to makes sense of the signals being generated. (6) In late 2000, Antti Revonsuo published a paper in "Behavioral and Brain Sciences," asserting that the content of our dreams is not as disorganized as the aforementioned theory claims and that there is an evolutionary explanation to dream content. In essence, Revonsuo is suggesting that dreaming was selected for during our evolution, (7) but why would this happen?. Stating that waking experiences have a consistent and profound effect on dream content, Revonsuo hypothesizes that there is a biological function to dreaming – to stimulate threatening events and rehearse the perception and avoidance of threats. Revonsuo argues that the ancestral human lifespan was short and full of threatening situations, therefore, any mechanism that would stimulate these situations and play them over and over in different combinations would be advantageous for improving threat-avoidance skills. Finally, Revonsuo asserts that this ancestoral mechanism has left some traces in the dream content of the present human population.

Since one cannot be certain of the validity of a hypothesis, it will prove helpful to discern which hypothesis seems "less wrong." Revonsuo's idea about the original purpose of dreams simply provides us with a more complete look at the story behind dreaming. That is to say, it is by no means a complete idea on its own. While it is interesting to think that some of the content of our dreams may have had an evolutionary function, it should be noted that dreams are not predictable. (8) Each person experiences life differently, and through dreaming, can create experiences that will be unique to them, therefore entering a "world of his own" as Plutarch suggested.

As modern-day humans, we are not faced with the same limitations as our ancestors. Our survival and chances of reproduction have little to do with our threat avoidance capabilities. So, if we assume that dreams initially served as a feature of evolution, what function, if any, does dreaming serve in humans presently? On the one hand, we could revert back to the original theory, with a twist. We can suggest that dreaming serves no real function at present. For example, people having suffered through traumatic ordeals often complain of nightmares. Dreamless nights would in fact be helpful in these situations, as far as mental health is concerned. So while dreams are sometimes a welcome escape from reality, other times reality is a welcome escape from our dreams. On the other hand, dreams perhaps serve a more fundamental purpose nowadays. In recalling our dreams, we are able to learn about ourselves using a broader spectrum of information. Above all, it is important to keep in mind, that we are all different. We therefore experience the world differently, react differently, and dream differently.


1)E-classics.com background on Plutarch

2)A website containing famous quotes about sleep

3)HowStuffWorks.com : Sleep, A simple explanation of the process of sleep.

4) The reinterpretation of dreams: An evolutionary hypothesis of the function of dreaming., Abstract from Behavioral and Brain Sciences, Dec 2000 v23 i6 p877.

5)Brain Basics: Understanding Sleep, A detailed explanation of sleep and dreaming from the National Institute of Neurological Disorders and Stroke.

6)HowStuffWorks.com: Dreams, A simple explanation of the process of dreaming.

7)Dreaming and Consciousness: Testing the Threat Simulation Theory of the Function of Dreaming, More on the Evolutionary basis of dreaming from Revonsuo, et al. PSYCHE, 6(8), October 2000.

8)From Genomes to Dreams, an essay by Paul Grobstein, Winter 1991, from the Serendip website of Bryn Mawr College.

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