Many psychologists agree that dreaming is intimately connected to the faculty of memory, but what is less clear is how. Different theories have been put forward to attempt to explain the relationship and why we find it so difficult to remember our dreams.
Most dreams occur during REM (rapid eye movement) sleep, the stage of the nightly sleep cycle characterized by increased electrical activity in the brain and, as the name suggests, rapid flickering movements of the eyes. Periods of REM sleep happen about five times a night, and it is estimated that most of us spend about two hours every night dreaming. That amounts to some 700 hours – about one whole month – each year. If this figure seems surprising, that is because we remember less than five percent of our dreams, mostly only those that take place in the last round of REM sleep. It makes sense that we should recall the dreams that we have just prior to waking up, but this does not explain why we forget so many of the others. After all, our brains are highly active every time we dream.
The erasing theory
In 1983, the biologists Francis Crick and Graeme Mitchison speculated that the reason why we forget 95 percent of our dreams is that our brains are designed not to remember them. They suggested that sleep is a time of ‘ unlearning, and far from neatly filing in memory everything we have experienced during the day, the brain deletes the vast majority of it as useless. According to this idea, dreaming is a side effect of a nightly review of the vast array of stimuli that bombard the brain via the senses every day. These perceptions are re-etched into the dense neuron networks of the cortex. The networks can become overloaded with sensory inputs and cease to function properly, so they need to be regularly cleared of irrelevant information – for example, the 208 times you glanced at a particular patch of the office wall today or the 20 times you looked at your watch. In Crick and Mitchison’s speculation, dreams arise from the activity of the brainstem in firing neural signals at the cortex to erase unwanted material and thus aid the storage of useful items.
The filing theory
Another speculation from psychologist Christopher Evans suggests that sleep has an active role in memory storage. Evans proposes that during sleep, the brain scans and puts in order all the hundreds of thousands of new sensory experiences we have in the day, filing them in the memory as efficiently as possible. From time to time during REM sleep, the brain becomes briefly conscious of this scanning and cataloguing process and tries to interpret the information in its usual way, as if we were awake and receiving stimuli from the outside world. This often disjointed stream of mental images is what we experience as dreams.
Dreaming and memory performance
The importance of REM sleep memory performance has been demonstrated by Israeli researchers Avi Karni and Dov Sagi, who trained volunteers to recognize patterns that appeared briefly on a computer screen. Each night, some volunteers were woken up in REM sleep while the others were left to sleep undisturbed. When they were all tested in the morning on the previous night’s task, those who had been woken performed less well than those who had not. There is still much to learn about precisely how dreaming relates to the consolidation of memories, but the process almost certainly involves a melding of new and existing memories. This could explain why our dreams often contain fragments of recent experiences mixed up with old ones.
How to Remember Your Dreams?
There are a number of techniques that can improve your ability to remember dreams, but one of the best is to keep a dream diary.
- Keep a small book and pencil on your bedside table so you can write down your dreams the moment you wake in the morning.
- Make sure this is the very first thing you do – being distracted by any activity, even turning over in bed, will hasten the fading of your dreams.
- Write your dreams in as much detail as possible on a left-hand page, leaving the right-hand page for comment and analysis later on.
- Include sketches to help you remember any striking visual images. Don’t forget to mention your feelings during the dream.
- A nightly review of the day’s events, starting with your morning account in the dream diary, can improve dream recall. Look for links and associations between dream memories and your daytime activities and feelings. This can help you to reach a fuller picture of your daytime – and night-time – self. As your proficiency at dream recall increases, you may also find that you are able to recall other experiences more easily.
Animal Dreams And Survival
As long ago as the 1950s, researchers in California put forward the idea that dreaming could have a role in animal memories. They discovered that rabbits, cats, and other mammals emitted a previously unknown type of brain rhythm called theta-rhythms from the hippocampus (a brain region) whenever they were exploring new territory or actively on the lookout for predators. The hippocampus emitted the same rhythms during REM sleep – in other words, when the animals were dreaming. The researchers proposed that, during REM sleep, the animals’ brains were replaying recent exiploratory experiences in order to reinforce in memory the information they yielded – such as new food locations or the territory of a rival.
One Australian mammal, the egg laying echidna or spiny anteater, shows no sign of dreaming during sleep. According to the above theory, this could be because the animal had virtually no predators until relatively recently and, therefore, did not need to develop enhanced memory faculties.
