What is Sleep?


        Sleep is, quite simply, a biologic necessity, a demanding human need that must be met by most of us daily, just like the need for food to eat, water to drink, and air to breath. Scientists have always known that everyone needs sleep, but none really understood what actually happened during sleep. It was generally believed that it was a time for the body and mind to relax and virtually shutdown. Only in recent decades have researches found out otherwise. With the development of new technology that allows researchers to measure the electrical activity of the brain (EEG recordings), scientists have discovered that sleep is a dynamic state of its own. Sleep is broken down into roughly five different physiological stages, or types of sleep.
        The first few minutes before the body and mind start to drift into sleep are referred to as “relaxed wakefulness.” Brain waves, when awake and in this relaxed state, are called alpha waves. This is the gateway to the first stage of sleep, drowsing. This is the relaxed state found between waking and sleeping. This stage is identified by a slower brain-wave pattern called the theta wave, which interestingly also occurs when daydreaming (Jacobs). When a fellow student is dozing in a boring class, or perhaps when they are reading a lengthy report on sleep, they are often easily awakened and they claim to just be drifting off but not actually asleep. This is stage one sleep, a light sleep, but not regarded as a true sleep.
        Stage two develops after a few minutes of stage one sleep. Stage two sleep is the first authentic sleep phase, and brain wave patterns exhibit sleep spindles and k-complexes (Jacobs). These are more or less surges, where the brain’s electrical activity jumps in a last attempt to maintain awareness. None the less, the outside world is calmer and more detached. This stage lasts between 30-45 minutes before it develops into the third and fourth stages of sleep.
The third and fourth stages of sleep are marked by very slow brain wave patterns named delta waves (Jacobs). This is when the body and mind are in a deep sleep and almost entirely shut off from the exterior world. Delta sleep is considered to be the time when the body is allowed time to recover (Hauri). There is no dreaming during these first four stages of sleep, called NREM or no dream sleep (Caldwell). Normally a person will undergo deep sleep for about 45 minutes and then they will go back into stage two sleep, wandering in and out between the three stages until they finally move on to dream sleep (Jacobs).
        Dream sleep is by far the most interesting stage of sleep, and yes, everybody does dream. It is commonly referred to as REM sleep meaning “rapid eye movement.” It is called this because we literally watch our dreams. During REM sleep, the brain and body display significant amounts of activity. Throughout the REM state, heart rates, blood pressure, and breathing rates escalate and become highly irregular during dreaming. Brain waves are similar during REM sleep to the brain waves found when awake. This is why REM sleep is also called paradoxical sleep (Jacobs). Sleep scientists call the time to the end of the first REM sleep the first sleep cycle, and the time from then to the end of the second REM sleep the second sleep cycle. A typical adult will return to REM sleep about every 90 minutes (and about every 60 minutes in infants). There are four to six cycles per night, depending on the length of sleep. The first REM period of the night is very short, lasting about 5 minutes, the second is about 10 minutes, and the third is roughly 15 minutes. The final dream of the night usually lasts for 30 minutes, but sometimes lasts an hour (Hauri).