Set of traces

      Stage 2: light sleep

      As you descend further into sleep, the relaxed alpha rhythm is replaced by a faster wave form of 12-14 cycles per second called a ‘sleep spindle’ (because of the spindle shape it makes on the computer screen). At this point the systems that maintain wakefulness are letting go and the sleep-promoting systems are switching on. This stage usually lasts 30-40 minutes.

      Stages 3 and 4: deep sleep, delta or slow-wave sleep

      Slow-wave sleep lasts for roughly the first three hours of the night and it is very difficult to wake people up from it. People who are woken at this stage often act quite strangely, almost as if they are drunk.

      must know

       Ultradian rhythm

       Scientists believe there may be a brain rhythm that is mainly revealed during sleep as a 90-minute REM cycle. As this lasts less than 24 hours it is known as an ‘ultradian rhythm’ (Ultra from the Latin for ‘beyond’). Dreams occur on a roughly 90-minute cycle.

      At the deep-sleep stage, the EEG shows highamplitude slow waves. The mind begins to drift, thoughts are unfocused, and the brain becomes ‘dormant’. A person in this stage of sleep tends to stop moving and their postural muscles relax. Heart rate and breathing slows, the body temperature ‘thermostat’ in the hypothalamus is lowered and body temperature reduced. Kidney function decreases and less urine is produced.

      Stage 5: Rapid Eye Movement (REM) sleep

      Stage 5 sleep is commonly known as Rapid Eye Movement, or REM sleep, named after the darting eye movements that have been observed in people in this sleep stage. It appears after 80-90 minutes’ sleep in recurring phases known as an REM cycle. It initially lasts for about ten minutes, then increases in length, with the final one lasting for about an hour. In young adults, REM sleep can last for up to two hours in total.

      For many sleep scientists, REM sleep is the most interesting and exciting of all sleep stages, for this is when dreaming occurs, and is when the brain is most active. In fact, curiously, EEGs taken at this time are more similar to those taken during wakefulness than at other sleep stages. The brain shows increased cerebral metabolism, cerebral blood flow, intracranial pressure and brain temperature, and many parts of the brain that control functions such as heart rate, blood pressure, breathing, body and brain temperature and sweating are less well regulated than at other times. Even sexual organs are aroused and men often have penile erections. In fact, there was a time when REM EEGs were used to determine whether men’s impotence was physical or psychological, though this has all changed in recent years with the introduction of Viagra.

      must know

       Are you a dreamer?

       If you don’t think you dream, try setting your alarm clock at 15-20 minutes earlier than your usual morning wake-up time. This will almost certainly ensure that you will be awoken out of REM sleep. Go to bed preparing yourself to remember what is in your mind when you wake up. When the alarm goes off, think about what has been going through your mind.

      REM sleep and dreaming

      Scientists believe we dream during REM sleep, and that the dreams become more vivid as the sleep stage progresses. Most REM sleep occurs towards the end of the night and can sometimes reach its peak in the early morning, (which is why you can often remember dreams clearly just as you wake up). But the memory of the dream usually fades within minutes.

      Sigmund Freud and dreams

      Although he originally trained as a doctor, Sigmund Freud (1856-1939) is best known for his study of the mind, and is often referred to as the father of psychoanalysis. Freud believed that the mind consisted of three main elements: the ego (the conscious self), the superego (the mind’s moral guardian) and the id (psychic and unconscious mental energy), and that the demands of the id, left unchecked during sleep, were expressed in dreams.

      In Freud’s psychodynamic theory, dreams symbolized unconscious thoughts and mental processes, and interpreting their meaning was a ‘royal road’ to understanding the subconscious mind. One of Freud’s contemporaries, Carl Jung (1865-1961), formulated the idea of the ‘collective unconscious’ (a reservoir of memories and experiences), his list of the many recurring themes in dreams including: water, being trapped, travelling, running, being chased, death, choking, falling, houses, flying, nudity, being late and sex.

      Freud’s influence on psychiatric thought has now largely declined, but his book The Interpretation of Dreams (1900) remains one of the most significant works of the 20th century.

      REM sleep has often been described as paradoxical because it has many contradictions. Although EEG readings show that the brain is so active at this time that it may be using even more energy than during wakefulness, the muscles, by contrast, are completely paralyzed, apart from rapid eye movements and the odd, involuntary twitching of fingers. Since vivid dreams also occur at this time, some people believe the muscle paralysis is there to stop the dreams from being physically acted out.

      did you know?

       During REM sleep your brain is as active as when you are awake.

      Dreaming through the ages

      Dreaming has intrigued and fascinated people for thousands of years before the works of Sigmund Freud, and many of the world’s greatest civilizations and religions have used dreams to guide their everyday lives. Let us look at some of the most famous examples below.

      did you know?

       An ancient Hindu tale that is still relevant today describes three states of mind: the state of wakefulness (vaiswanara), when a person perceives ‘what is presented to them by their senses’, the state of dreaming sleep (taijasa) ‘which can reflect in the mind what has happened in a person’s past’, and the state of dreamless sleep (prajna) when ‘the veil of unconsciousness envelops thought and knowledge, and the subtle impressions of the mind apparently vanish’.

      The ancient Egyptians

      By around 2000 bc, the ancient Egyptians were already transcribing their dreams on to papyrus. Egyptians believed that dreams brought messages from the gods and that dreaming was the best way of attaining divine revelation. They developed methods for inducing or incubating dreams, including building sanctuaries that had special beds for dreaming.

      The ancient Greeks

      Sanctuaries and shrines for promoting dreams were also adopted by the Greeks, who in addition had specific dream rituals. Those entering the Shrine of Apollo at Delphi were required to abstain from sex, or eating meat, fish and fowl two days before. Once in the shrine, they made an animal sacrifice to the god from whom they wanted to receive the dream and would then sleep on the skin of the sacrificed animal, sometimes near the statue of the appropriate deity. The Greek god Hypnos was thought to bring sleep to mortals and his son Morpheus was said to send warnings and prophecies to those sleeping in the temples.

      The early Christians

      The Judeo-Christian tradition also used dreams as a guide to waking behaviour, most notably in the story of Jacob’s dream of the ladder going up to heaven recounted in Genesis, which was seen as a turning point