Why do people dream, and more specifically why do children sleep and dream so much in their early stages of development? Prior to the current advancements in brain imaging techniques and cognitive sciences, researchers viewed dreaming simply as the result of random neural activity.

Hobson and McCarly’s, 1977, activation-synthesis hypothesis states that dreams are the result of random neural noise generated in the brainstem, the lower part of the brain where all the information to and from our body passes through, that is interpreted by the forebrain, the part of the brain that controls cognitive, sensory and motor functions, in such a way that leads to the subjectively phenomenology of dreaming.

Until recently, this hypothesis fitted well with cognitive models and with the very randomness and difficulty of how each and every one of us is able to recollect and report information from recent dreams in a coherent way. The apparent randomness of dreams is somehow explained by this theory. But could this be all? Nope. Mother Nature doesn’t place dice, indeed! Every behavior, every physical and cognitive trait, every piece of something that a certain organism is endowed with must have an purpose in the real world. And i am going to say, yes, this is also true for dreaming. Although this article is not going to represent a plea in favor of adaptationism, we are going to treat dreaming as a certain adaptive trait that evolved in mammals, reptiles and birds due to specific environmental pressures, trait that might give us a hint about the complexity of the effects those pressures had on mammals, and consequently on homo sapiens, so that they needed to evolve this special tool of dreaming.

        Let’s clarify the mechanism of sleeping before we delve into the reasoning for dreaming’s purpose. From the first step of entering sleep towards the final one, the brain goes through several stages of neural activities that are characterized by certain levels of activation of neurons from specific parts of the brain. With the help of electroencephalography (EEG), electro-oculography (EOG) and electromyography (EMG) scientists categorized the different arousal states specific to each stage of sleep, by studying the level of brain activity, eye movements and muscle activity a certain individual has under sleep. Some arousal states will be characterized by a slow brain activity, other by a fast brain activity, but a certain stage of sleep, which makes the subject of this article, is the REM (rapid eye movement) stage where the brain goes through a hyperactive condition where the brain mimics the waking brain, that is, the state at which the brain is when it is awake.

What makes the REM stage of sleep so special? It is special because the younger we are, the more REM sleep we need to have, but more importantly because REM sleep has long been associated with deep and lucid dreaming. Studies have shown that people awakened from their REM stage had been able to report more detailed and vivid dreams than those awakened from thei NREM (non-REM) stages of sleep. What happens in the REM? First of all, the brain is more active than in the other phases of the sleep process, the EEG showing both alpha and beta neural activity; although all the muscle motor controls are inhibited and physical paralysis is induced, rapid eye movements still occur because the paralysis does not extend to the eye muscles.

So the overarching theme is that unlike NREM, where dreams are reported less frequently and are lacking vividness and often contain a simple reccuring theme, REM sleep seems to be endowed with a special kind of consciousness that makes large samples of individuals report dreams as realistic and as containing a connected and coherent storyline. So, this conclusion seems to be in total contrast with the activation-synthesis hypothesis we mentioned above, that stated that dreaming, specifically REM dreaming is only a neurological quirk with no special use or property, caused by the random noise of the brain. If the random noise in the brainstem is the cause, why all the linearity and coherence that the dreamers report in REM compared to the randomness and non-linearity of rarely reported dreams in the N-REM stages of sleep?

        Revonsuo’s Threat Rehearsal Theory answered the above question. The theory proposed that REM dreaming serves as a virtual threat simulator, adapted and molded to the specific recent environmental stimuli that a certain individual might be subjected to in his current natural environment, in order to train and prepare him/her for actual life threatening situations he could encounter and could potentially cost him his life. Here we have it. Natural selection may have invented virtual reality simulators long before the wisdom of homo sapiens sapiens cared to intervene.

But how could dreams have the ability to train our brain? Just like most successful people reveal that their most biggest secret to their life success is their ability to imagine themselves successful, just like most famous baseball players, even when not physically rehearsing, imagine themselves swinging their bat towards their next home run, the same way the brain, while REM dreaming, activates the same brain regions that would be active while being awake and prepare the dreamer for real life threatening situations. The individuals that possessed the above ability, that is, our ancestors who had the ability to simulate real-life threatening situations during REM sleep, were favored by natural selection and their offspring, that is us, are the only ones alive today thanks to that adaptation.

Even though there seems to be some kind of plasticity involved in the simulations played in dreams based on the specific environmental factors that act on the individual’s life, so that randomness has a more reduced impact on the simulations made in REM sleep than those in NREM, a certain amount of randomness in the situations created in the virtual simulations still persists, thus confirming that the activation-synthesis hypothesis might still be used to explain the variability of future real life simulations dreams are able to prepare us for.

        But could there be another advantage REM dreaming might come with? Certainly YES! That’s what Michael S. Franklin from The Department of Psychology at University of Michigan and Michael J. Zyphur from at Tulane University tried to prove in their 2005 paper. The main idea? Rather than being a threat rehearsal mechanism, dreaming may be a more general virtual reality simulator that is likely to play an important role in the early development of human cognitive capacities. That is why REM sleep occurs most frequently in newborns, and generally decreases throughout ones lifespan. “Newborns can spend about eight hours a day in REM sleep, and REM sleep actually occurs at sleep onset (Winson, 2002)”. As we age, the less REM, but the more N-REM sleep we get. The scientists argue children charge their brains with vast amounts of important sensory information while awake, and, while in their long REM sleep, they model and shape this information to develop a behavioral model specifically designed to their social and environmental situations.

Want to find out more? Here is a list of Highly Rated books on Amazon.com about the body’s biorhythm from which you can learn more about REM sleep and how the brain works:

References:
- EVOLUTIONARY PSYCHOLOGY JOURNAL 2005 -> The Role of Dreams in the Evolution of the Human Mind