The Dream Dictionary from A to Z [Revised edition]. Theresa Cheung

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      We know that sleep is essential for our well-being but, like dreams, sleep remains a tantalizing mystery. It may surprise you to know that, to date, sleep researchers have not yet discovered the exact reason for sleep. For centuries it was thought that we needed to sleep to rest the body and mind, but this was disproved in the 1920s with the first electronic monitoring of the brain.

      The brain gives off electrical impulses, and by attaching electrodes to various parts of the head scientists measure brain waves in a process known as electroencephalography. What these brain-wave readings (or ECGs) show is that both the body and the mind are active during sleep. So, if sleep doesn’t rest either your body or your mind, what is it for?

      We don’t yet know for sure, but sleep researchers have uncovered some very intriguing things. It seems that when we fall asleep our brains act a little like computers that are offline. This means they are not idle but filing and updating. They do a system check on your body and release hormones to repair damaged tissues, stimulate growth, and fight infections. Sleep is therefore vital for the smooth running of many functions of your body and your brain, including memory, problem solving, and attention. Lack of sleep can lead to dementia, high blood pressure, heart disease, cancer, premature aging, weight gain, and lowered immunity. In short, sleep is essential, and we spend up to a third of our lives doing it. But despite all this we still aren’t entirely sure why we need it, and most doctors still don’t pay enough attention to the obvious importance of sleep for our physical and mental health.

      However, the advent of space travel – of all things – has taught us a little more about sleep and why we need it. Scientists found that the prolonged periods of isolation and lack of external stimulation experienced by astronauts dramatically decreased their need for sleep. There is a sleep control center in our brains and when that gets overloaded with external stimuli we get tired. This explains why sometimes you nod off for no reason. Sleep is so crucial that your brain decides you have had quite enough stimulation and it’s time for you to switch off and recharge. If, however, there has not been enough stimuli from the outside world the sleep mechanism isn’t triggered, and you remain wide awake.

      In other words, boredom, loneliness, routine, and the resulting lack of stimulation may account for episodes of insomnia. Although, paradoxically, it is worth noting that overstimulation has also been shown to trigger insomnia. Once again, whenever we edge closer to explaining the whats and whys of sleep, the plot thickens and the mystery remains.

      The Stages of Sleep

       Yet it is in our idleness, in our dreams, that the submerged truth sometimes comes to the top.

       – Virginia Woolf

      Perhaps the best way to learn more about sleep and why we need it is to understand what happens to our brains when we fall asleep.

      Sleep researchers believe there are at least four stages of sleep, starting from when you begin to doze to when you lose conscious awareness and transform from a waking into a sleeping state. These stages are cyclic and repeat up to four or five times for every eight hours of sleep, each cycle lasting around 90 to 120 minutes. Here’s a brief, and by necessity, simplistic description of what typically happens when you go to bed at night.

      During the first stage of sleep, when you lie down and close your eyes your body and mind relax. Heart and breathing rates slow down, blood pressure lowers, temperature drops, eyelids grow heavy, and eyes roll from side to side. During this stage you are semi-conscious and can easily awake. When people are sitting or traveling and they start to doze off, they struggle to keep their heads upright. This is stage one. It’s often called the hypnagogic state (the hypnopompic state is when you are just waking up) and it’s when you are most likely to experience hallucinations that float before your eyes.

      In stage two, breathing and heart rate slow even further, eyes continue to roll, and you become more and more unaware of external stimuli or the noises from the outside world. It isn’t until the third and fourth stages of sleep, though, that you are finally sound asleep and it is harder to wake you up. You are now in a deep sleep state known as non-rapid eye movement (NREM) sleep.

      In NREM sleep your brain is released from the demands of your conscious brain and it is rather difficult to wake you. This slow brain-wave sleep cycle typically lasts around 90 minutes. At the end of stage four you move back through stages three, two and one, at which point you enter a fifth stage of sleep called rapid eye movement or REM sleep. This is when things start to get really interesting and the dreams begin.

       REM Sleep

       One of the most adventurous things left us is to go to bed. For no one can lay a hand on our dreams.

      – E. V. Lucas

      REM sleep is defined by tiny twitches of facial muscles and slight movements of the hands. Blood pressure rises, breathing and heart rate become faster, the brain is fully active and eyes dart rapidly under closed eyelids as if you were looking at a moving object. If you are a man you may have an erection.

      Although dreams can occur during NREM, researchers have discovered that it is REM sleep which is most associated with dreaming. When sleepers are awakened during REM sleep, they typically recall their dreams. Sometimes people feel temporarily paralyzed if woken during REM, as if something heavy and/or malevolent is pressing down on them. This phenomenon may explain supposed succubus, incubus, and alien abduction experiences.

      The first stage of REM sleep lasts around 10 minutes and then you fall back into stages two, three and NREM sleep again, and keep moving backwards and forwards between the stages through the sleep cycle. As the cycle continues, however, the REM phase gets longer and longer, with the longest phase lasting up to 45 minutes. Of all the phases of REM and NREM sleep, the final REM phases are the ones from which you are most likely to recall your dreams.

      The emotional center of the brain is more active than the logical center when we are dreaming. But, intriguingly, scientists have found that dreaming about faces is linked to the areas of the brain involved in facial recognition when we are awake, suggesting that the dreaming and waking brain may not be as different as is often thought.

       We Sleep to Dream

       And one day there will come a great awakening when we shall realize that life itself was a great dream.

      – Chuang-Tzu

      Experiments have proved that sleep is essential for life. Rats typically live for two to three years; rats deprived of all stages of sleep live for about three weeks, and rats deprived of only REM sleep survive for about five. Other research has shown that both NREM and REM sleep are essential for preserving memory, but if people are repeatedly woken during periods of REM sleep – which means they are deprived of their dreamtime – they become anxious, irritable and stressed. This suggests that all stages of sleep are vital for physical and mental health, and REM sleep – when you are most likely to dream – is essential for your emotional and psychological well-being.

      Therefore, although we still don’t know why we sleep, it is entirely possible that one of the major reasons we sleep is to dream.

      How Much Sleep Do We Need?

      We spend up to a third of our lives sleeping, which means that if you reach the age of 100 you will have been asleep for around 33 years. The amount of sleep each person needs to feel healthy and think clearly depends on many factors, including age and activity СКАЧАТЬ