Nearly every animal sleeps in some way. It is evident that sleep performs some vital function for the nervous system, because without it, we would die. That said, experiments in sleep deprivation have shown that it is not, in fact, a lack of sleep that causes people to be disturbed, but dream deprivation that lies at the root of the problem.
Many theories have been suggested about the purpose of sleep, and the most practical seems to be one put forward by Nobel prize winner, Francis Crick (of Watson & Crick DNA discovery fame), who claims that our nocturnal habit of sleep is simply to allow the brain to “take the trash out”, that is, to undo all the daily events that do not need to be stored for long-term memory.
Put another way, we humans need to get rid of unimportant mental items that are literally clogging up the brain. We can thus recharge during sleep in order for nerve cells to be re-engaged the next day to face the onslaught of a new set of challenges!
There are four stages of sleep:
- The first stage is a very light sleep. You can easily be woken and, upon awakening, might even deny having been asleep at all. Ever heard anyone say, “I wasn’t asleep, I just had my eyes closed”? That’s because the brainwaves are going from a waking frequency (beta) to a more relaxed phase, known as alpha state. This is when the body temperature, heart and pulse rate drop slightly and the eyes begin to roll. Drifting thoughts and floating sensations as well as vivid pictures flow through the brain. Stage 1 can last five to ten minutes. You are on the edge of sleep.
- In stage 2, the brainwaves keep on slowing down. This is a much deeper sleep than stage 1 and is when dreams start to brew. Although there are no clear images, thoughts and ideas float in and out of the sleeper’s mind. The brain frequency has now reached a level called theta. Snoring is common at this stage and there is a decreased heart rate, pulse, blood pressure and temperature. Breathing can be shallow and irregular. Ever had a twitch or jerk but still felt unable to shake yourself awake? This is the stage where it happens. More importantly, the eyes now move back and forth rapidly beneath the closed eyelids. This is known as REM (rapid eye movement) sleep and lasts for a few minutes the first time it occurs. If you wake up at this time, the dream can usually be remembered.
- Stage 3 is the deep sleep stage, with stage 4 being even more intense. These stages are known as slow-wave or delta sleep. These long, regular delta waves produce a deep, dreamless sleep. The sleeper’s muscles are totally relaxed and the heart rate and blood pressure have slowed right down. Breathing is steady and even and it’s going to be very difficult to wake up from this stage. Delta waves can last up to an hour before the dreamer goes into the deeper sleep of stage 4.
- This is the deepest sleep and almost impossible to wake up from this stage. The sleeper’s blood pressure and heart rate fluctuate. There is an increased secretion of growth hormone (to restore body tissues), which is why it is so important for infants and children to get as much sleep as possible. This is the stage when dreams occur again and REM is at its best because the brain is in an active state. The first REM period will last approximately ten minutes. After that, the sleeper goes back into a deep stage 4 sleep. Then it’s back into REM stage after a short time and the cycle is repeated until the sleeper eventually wakes up. The final REM stage lasts about one hour.
These four phases of sleep repeat four or five times during the night, approximately every 90 to 120 minutes. A person may, therefore, complete up to five cycles in a typical night’s sleep, with the REM stage lasting longer the more one sleeps. The longest uninterrupted period of dreaming occurs during early morning and may last up to one hour. So, if you find yourself waking up between the hours of 3 and 5 in the morning, don’t get mad ……make the most of the interruption as, ironically, they are likely to be the most creative two hours you’ll experience in the day!