ELECTROENCEPHALOGRAPH, a device for recording the electrical activity of the brain. The graph on which the electrical impulses are recorded is known as an electroencephalogram, or EEG. An electroencephalograph is capable of recording from 8 or more areas of the brain simultaneously. For each pair of electrodes it has a channel of amplification and an ink-writing voltmeter that records on folding paper tape. Electrodes placed on the scalp pick up impulses that arise from the outermost area of the brain, the cerebral cortex. To record the electrical activity of deeper regions, needle electrodes can be surgically inserted into those specific areas.
Uses. The electroencephalograph is valued as an important diagnostic and monitoring aid as well as a research tool. It is used to diagnose brain injury caused by traama, infection, hemorrhage, insufficient blood supply, or a tumor. It can also be used to determine the location of an injury within the brain. The electroencephalograph is also used for determining whether an inflammatory or epileptic reaction to an injury has occurred, and if so, to determine whether it is getting better or worse.
Anesthesiologists use electroencephalographs to indicate the depth of anesthesia and after surgery, to monitor the patient’s recovery. Critically ill patients can be watched to see if they are sinking into a coma, or, if already in a coma, to determine if they are getting better or worse. Sometimes a patient’s heart continues to beat and he continues to breathe, but higher levels of brain activity do not function. In such cases known as irreversible coma, the electroencephalogram shows no brain activity (electrocerebral silence).
In research studies, the electroencephalograph is widely used for studying the various stages of sleep. It is also employed to study the eftects of drugs on’ the brain.
History. The first electroencephalograms of man were made by the German psychiatrist Hans Berger, who published his results in 1929. He used a string galvanometer that registered photographically on moving film or bromide paper. This was the standard apparatus used at the time for making electrocardiograms, graphs of the electrical activity of the heart. Berger’s first reports were greeted with skepticism by the majority of scientists, but gradually the electroencephalograph became accepted as an important diagnostic and research aid.