The study of sleep is now a serious science. There are more than 170 sleep clinics and sleep laboratories in the USA alone. Sleep laboratories are designed for conducting research on sleep; they are also used to diagnose and treat sleeping problems. They are usually situated within the larger hospitals or attached to the medical schools and universities.

The first sleep laboratories were set up about 50 years ago. Scientists began to measure the electrical activities of the brain. Our brain is made up of a huge number of brain cells, and messages, in the form of electrical impulses, are transmitted from one cell to another cell and so on. This creates many electrical circuits, very much like the microchips of the present day computers. These circuits in the brain are always conducting messages, which generate electrical potentials. These electrical activities can be picked up by electrodes located outside the scalp and recorded on a moving scroll of paper as oscillating waves.

The machine which records brain waves is called an electroencephalogram or EEC It is now possible to distinguish several different kinds of wave forms according to the frequency and shape of the waves. When a person sits quietly with his eyes closed, the wave form is quite regular and the frequency is about 8 to 13 cycles per second. This is called the alpha rhythm. It is noticed that when a person falls asleep, the wave form changes to slower and slower waves. The EEG is now the most reliable objective way of telling whether a person is falling asleep and of judging how deeply he is sleeping.

Nowadays, with the advance of organ transplant between bodies, the surgeon has to know when a donor body is really dead before any of its organs can be removed and put into a recipient body.

This is especially important in the case of heart transplant, as the surgeon has to remove a beating heart from a donor body and place it into a recipient body with a failing heart. The EEG is used to determine if the brain is alive or not. When the EEG is silent and not recording any activity, the person is said to be brain dead. If a person is brain dead he is truly dead, and his organs can be used for transplant purposes. In 1976, at a conference of the Royal Medical Colleges, unanimous agreement was reached for the clinical diagnosis of brain death and very strict criteria have to be satisfied by clinicians before brain death can be pronounced.

When a person falls asleep from the fully awake state, he enters stage 1 sleep, which is a very light sleep. This is followed by stage 2, stage 3, and stage 4 sleep, where stage 4 is the deepest sleep. These four stages of sleep are differentiated by the characteristics of the brain wave forms as recorded by the EEG. Stage 1 light sleep occupies only 5 per cent of all these four stages put together, while stage 2 sleep appears to be the most important stage, occupying 50 per cent. The waves become slower and bigger as the person sleeps deeper and deeper. In stage 4 sleep, the brain wave frequency is only 3 cycles per second. Both stage 3 and stage 4 sleep are called slow wave sleep.

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