Dreams have fascinated philosophers for thousands of years, but only recently have dreams been subjected to empirical research and concentrated scientific study. Chances are that you’ve often found yourself puzzling over the mysterious content of a dream, or perhaps you’ve wondered why you dream at all.
"One theory is that it's a way of allowing your brain to recover and consolidate all the memories and activities of the previous day, like filing time," The Daily Telegraph quoted Prof Drew Dawson from the Centre For Sleep Research at the University of South Australia, as saying.
He added: "If we give someone a complex new task to learn and we let them sleep but don't let them dream, they're almost as bad the next day as if they didn't sleep at all."
What purpose do dreams serve? While many theories have been proposed, no single consensus has emerged. Considering the enormous amount of time we spend in a dreaming state, the fact that researchers do not yet understand the purpose of dreams may seem baffling. However, it is important to consider that science is still unraveling the exact purpose and function of sleep itself.
Some researchers suggest that dreams serve no real purpose, while others believe that dreaming is essential to mental, emotional and physical well-being. Ernest Hoffman, director of the Sleep Disorders Center at Newton Wellesley Hospital in Boston, Mass., suggests that "...a possible (though certainly not proven) function of a dream to be weaving new material into the memory system in a way that both reduces emotional arousal and is adaptive in helping us cope with further trauma or stressful events."
Many people mistakenly believe "dream sleep", or rapid eye movement (REM) sleep, is the deepest stage of sleep.
According to Prof Dawson, humans were more deeply asleep prior to dreams. The average sleeper went through several sleep cycles a night, each lasting about two hours and finishing with REM.
Prof Dawson said: "Your brainwaves while you're dreaming actually look very similar to your brainwaves when you are awake."
This has led some scientists to theorise that dreaming is an evolutionary survival mechanism, which helps keep our brain alert.
Prof Dawson said: "It might prevent you getting so deeply asleep that you would be vulnerable if you needed to wake up quickly."
Brainwave tests on animals demonstrate all mammals dream, however, whether dogs and cats and other species actually have visual dreams is impossible to know.
Prof Dawson said: "It's reasonable to think they probably do, but we don't know for sure."
Sleep and fatigue expert Dr Stuart Baulk believes humans were essentially paralysed when they entered dream sleep, with muscle tone changing to prevent the body moving around.
Occasionally, some people experienced "sleep paralysis", where they woke and were fully conscious but still paralysed and seeing dreamlike images.
Dr Baulk said: "Although you see the room around you like normal, you might still get the images from a dream."
The brain is constantly matching patterns, asking in effect, "what is this incoming sensory information like?" It is continually comparing and contrasting the incoming data it receives for similarities with innate instincts or memories so it can know what to expect. It has to do this in order to decide how to act. This is known as 'metaphorical pattern matching' and is why the unfulfilled emotional expectations left over from the day are run out in the form of metaphors in dreams during REM sleep. Without this happening the brain would not be freed up to deal with any new emotionally arousing events the following day.
There are good reasons why all dream content is metaphorical and not directly about the concerns of the day. Firstly, the brain cannot generate "real world" reality without feedback from the environment. So, since all our senses are switched off whilst we are dreaming, instead of the brain seeking to fulfil the patterns of arousal externally, it does so internally, drawing on memories that have emotional and metaphorical resonances with the unresolved arousal patterns in the autonomic nervous system. This is why dreams often seem so odd; they draw on memories and images from your entire life, even though they are only about unacted out arousals from the previous day. So every person you see in a dream is standing in metaphorically for someone else in real life.
Secondly, without using metaphorical translations the brain would either be forced to create false emotional memories or be left with massively significant gaps in memory.
In the first case if the brain acted out unexpressed waking expectations and committed that experience to memory it would have created false memories. It could, of course, be argued that we have the ability to distinguish dreams from waking reality. But that would be missing the point. The emotional conditioning of our reactions would have still taken place even if we were subsequently able to separate dreams from real memories. Just as someone with a phobia of spiders, who knows intellectually that they are not a real threat to them, still has the emotional conditioning triggered off and scream whenever they see one.
On the other hand, if the brain chooses to forget the dream (which is what happens) it would create gaps in memory for what actually happened since the dream will involve both real and fantasy experiences. This would be equally disastrous because a memory system with significant memories missing would be next to useless as a basis for predicting the future, as is the case with people suffering from Alzheimer’s disease. By using analogy or metaphor whilst dreaming the brain can discharge the arousal, safely forget the metaphorical dream material and keep the original record of what really happened filed away in memory.