A theory of dreaming
It is difficult to explain the function of dreaming. Despite many theories, scientists still do not completely understand its purpose. What we do know so far is that dreaming is a way of shuffling and sorting through various events that happen during your waking hours.
A dream is the succession of images that pass through your mind during sleep. Perhaps dreams are our way of confronting our lives and dealing with things. Our brain pulls out information and incidents and sorts them through memories, deciding which ones to retain and which ones to lose.
Among the best explanations for dreaming is the psychosomatic theory of dreams. It suggests that dreams are a product of ‘disassociated imagination’ which is disconnected from the conscious self and which draws material from sensory memory – with the feedback resulting in the visions we experience.
Polysomnographic record of REM sleep, which provides data regarding electrical and muscular states during sleep. EEG highlighted by red box. Eye movement highlighted by red line.
REM dreaming stage
Human sleep consists of six recurring stages that are independent of one another. These include four non-REM stages, one REM stage, and finally the waking stage. The most vivid dreams occur during the REM stage of sleep – the stage of sleep during which there is rapid movement of the eyes.
About 4-5 periods of REM sleep occur during a normal night of sleep. The eye movements at this stage are associated with PGO Waves (Ponto-geniculo-occipital waves) and are generated by the pontine nucleus, with projections to the major component of the vertebrate mid brain, called the superior colliculus. In this stage, respiration and heart-rate speed up, resulting in increased brain activity, muscular immobility and a change in the neuromodulatory systems.
Does REM sleep occur in all animals?
We know that most if not all animal species experience some form of sleep. Studies so far show that REM occurs in all mammals. Dolphins, for example, exhibit some sort of REM sleep, and during slow-circle-swimming they allow half their brain to sleep at a time.
But what about reptiles? Being ancestors common to birds and animals, we might expect that reptiles exhibit REM sleep. But this is not the case. Reptiles don’t have brain development like mammalians and also do not have a neocortex. Therefore, they don’t exhibit REM sleep. And even if they did, it would be quite different from that of mammals. More studies are needed in this area.
Who dreams the most?
Studies suggest that the percentage of REM sleep is highest during early childhood. The more immature a person is, the more dreams they should have.
Cats, dogs, pigs and of course humans all dream. But koalas and brown bats might be the dream kings simply because they sleep for so long (around 20 hours a day). Giraffes and elephants, on the other hand, sleep very little – only 3-4 hours a day. (Read more about the sleepiest animals).
One final point: even though we dream a lot, within 5 minutes of waking most of it is gone. It is a common tendency to forget 90-95% of our dreams.
In closing, a quote about dreams by Oprah Winfrey that sums them up well: “The best thing about dreams is that fleeting moment, when you are between asleep and awake, when you don’t know the difference between reality and fantasy, when for just that one moment you feel with your entire soul that the dream is reality, and it really happened.”