When an EEG is used

The brain is well protected in the bony skull cavity. In the case of disturbances, it is therefore necessary to resort to methods for diagnosis, which also indirectly identify possible causes and their localization. In addition to x-ray and MRI examinations, an EEG (electroencephalography, brain current examination) is in many cases well suited for this.

Electroencephalogram in use

The brain works incessantly. This activity of large nerve cell associations manifests itself through electrical discharges, which can be seen as potential fluctuations on the surface of the brain and can be measured there. For this purpose, several metal plates are attached as electrodes at certain intervals on the skull surface and recorded the intervening voltage fluctuations (electrical potentials) in a graph, the electroencephalogram. The abbreviation EEG is used both for the entire examination (electroencephalography) and for the generated graph (electroencephalogram).

Examination with EEG

Since the EEG is risk-free for the person examined, it is carried out as a routine examination in certain clinical pictures. It can give unspecific information on metabolic diseases. Also, inflammation, tumors or dysfunctions of the brain are often manifested in the EEG. In patients with coma, electroencephalography may indicate underlying disorders. The first-choice examination method is the EEG, especially in patients with a tendency to epileptic seizures. This can be z. B. determine the location from which the spasms go out. In addition, electroencephalography is an essential part of the diagnosis of brain death.

Course of the investigation

The patient should not have previously had any stimulating drinks such as coffee, tea or cola. Freshly washed hair is an advantage. The doctor must be informed about which tablets are taken, as some may affect the course of the EEG. The examination is painless, harmless and can be repeated as often as required. About 20 electrodes are placed evenly on the scalp. The routine examination takes about half an hour at rest with the eyes closed. In between, the patient is asked to open his eyes, close them again and breathe heavily.

In special cases, the examination is carried out for 24 hours (long-term EEG, usually with a portable device) or especially during sleep (sleep EEG), sometimes provocation methods such as sleep deprivation or flashes of light are used. This can possibly diagnose an increased spasm readiness. In addition, a video recording (video EEG) can be made during the examination to see if certain phenomena such as blinking are associated with a seizure.

Evaluation of the electroencephalogram

The electrical brain activity depends on what work the brain is doing. The recorded curves in awake, relaxed people (alpha waves) have a different rhythm than those in mental activity (beta waves), during sleep or in diseases (delta and theta waves). In addition, the curve looks different in children than in adults.

When evaluating the graph, the doctor not only looks at which curves occur, but also whether they are deformed, what frequency they have (ie how fast or slow they run) and whether they are regular or shape specific patterns. In addition, he examines the curves at the various locations of the derivative and can thus provide information on a local event ("Herd findings"), z. As a tumor, a circulatory disorder or bleeding.

Decisive in the assessment is the overall picture, which is composed of the individual points. Only in rare cases, a change is so typical that it can conclude on a very specific disease - so causes z. B. encephalitis caused by herpes viruses a very specific course of the curve. In brain death, no brain activity is detectable - therefore, only straight lines (zero-line EEG) appear in the EEG. Since the time of death is equated with the irretrievable loss of function of the brain, such a zero-line EEG over 30 minutes is one of the indispensable prerequisites for declaring a patient dead and z. B. be allowed to remove his organs for transplantation.

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