Electroencephalogram (EEG)

An electroencephalogram (EEG) is a graphic (vivid) picture of the electrical activity of the brain. An EEG is made by placing electrodes (small terminals which conduct an electrical current) on the subject's scalp and connecting the electrode wires to a machine known as an electroencephalograph. The electroencephalograph then records the patterns of brain waves (rhythmic changes in the electric impulses of the brain.)

EEGs are used to diagnose epilepsy (a disorder marked by severe seizures or convulsions), brain tumors, strokes, and other neurological (nervous system) conditions. These conditions are characterized by distinctive, abnormal patterns of brain waves. EEGs are also used in investigating psychiatric disorders, such as schizophrenia (a psychiatric condition in which a person's sense of reality is severely distorted). In addition, EEGs help in defining brain death (the measurable end of brain activity). This diagnosis is necessary before the donation of organs for surgical transplants.

Making an Encephalogram

Hans Berger (1873-1941) was a German psychiatrist who developed the first human EEG in 1924. Berger was interested in psychophysiology (the study of the relationship between mental processes and the brain). Berger decided to measure the brain's electrical activity in the hope that the physiological record would provide insight into mental processes.

Berger began his search for the human EEG by experimenting with dogs. He moved on to humans and started placing needle electrodes under the scalp of patients who had lost some of their skull bones in surgery. It was while working with one of these patients that Berger recorded the first human EEG in 1924. At first, he was uncertain whether the oscillations (changes or variations) he had recorded originated in the brain. It was not until after he had conducted many other experiments that he published his first paper on the human electroencephalogram in 1929.

The initial reaction of others to Berger's work was one of disbelief. The scientific world doubted whether the workings of an organ as complex as the brain could be recorded through the skull. Berger did not achieve an international reputation until 1934. It was then that Edgar Douglas Adrian (1889-1977), a renowned English neurophysiologist (one who studies the functions of the nervous system), confirmed Berger's findings.

BEAM Enhances the Value of the EEG

Since the time of the original study, research scientists have used the EEG to identify the sources of brain activities. They have located the parts of the brain involved in the mental processes of reasoning, memory, and feeling. Interpreting the EEG was made easier in the 1980s with the use of the BEAM (brain electrical activity mapping) system. This system was invented by Frank Duffy of the Harvard Medical School. It uses computer technology to combine the signals from the individual electrodes into a overall, color-coded map of the brain's electrical activity.

Using the computer, BEAM can handle a wide range of tasks. It can store large amounts of EEG data, compare healthy profiles with abnormal ones, and provide detailed analyses. These analyses have been used to accurately diagnose such conditions as dyslexia (a condition marked by a difficulty with reading) and schizophrenia. Both of these conditions are usually difficult to detect.

The Future of BEAM

Efforts are currently underway to use BEAM in matching EEG patterns to specific brain functions. For example, research scientists have used BEAM to map the electrical activity involved in the movement of a monkey's arm. The studies have shown that when the monkey anticipates moving its arm, the pattern of electrical activity in its brain changes. If efforts like these are successful, it may one day be possible to use computers and the electrical activity of the brain to control the movement of artificial limbs.