When scientists confirmed some sixty years ago that the brain generates electrical impulses, the term ‘brainwave’ came into the language. It became common then, as it is now, for somebody to exclaim on getting a bright idea, ‘I’ve had brainwave’. The brain gives off electrical impulses all the time – not just to applaud brilliance. The heart, too, generates electrical currents, and its output is much stronger than signals from the brain. Specialists record both kinds when studying disorders.
The brain’s electrical impulses can be detected and measured by an electroencephalograph, or EEG. The patient has several small electrodes attached to the unshaven scalp. Next, reactions are measured while looking at a bright, flashing light. Sometimes, the brain’s impulses are recorded while the patient sleeps. An advanced version of the EEG is known as BEAM, for brain electrical activity mapping. With each system, a moving graph records the brainwaves’ patterns.
According to their frequency, brainwaves may form a mixture of two to four patterns. When you are relaxed and awake, but with your eyes closed, your brain gives off alpha waves, Beta waves produce a busier pattern, and come when you are active. If tests are performed while you are asleep or anesthetized (or, in rare circumstances, suffering from severe brain damage), the graph will show a wider-spaced, more regular pattern of delta waves. A similar but more concentrated grouping is made by theta waves, the dominant brainwaves of young children; in adults, they are sometimes a sign of abnormality.