The brain lies well protected in the cavity of the bony skull. In the case of disorders, one must therefore resort to procedures for diagnostics that also indirectly reveal possible causes and their localization. In addition to X-ray and magnetic resonance imaging, an EEG (electroencephalography, brain wave examination) is well suited for this purpose in many cases.
Electroencephalogram in use
The brain works ceaselessly. This activity of large clusters of nerve cells is expressed by electrical discharges that show up as potential fluctuations on the surface of the brain, where they can be measured. For this purpose, several metal plates are attached to the surface of the skull as electrodes at specific intervals and the voltage fluctuations (electrical potentials) derived between them are recorded in a curve image, the electroencephalogram. The abbreviation EEG is used for both the overall examination (electroencephalography) and the curve image produced (electroencephalogram).
Examination with EEG
Because EEG is risk-free for the person being examined, it is performed as a routine examination for certain medical conditions. In this context, it can provide nonspecific indications of metabolic diseases. Inflammations, tumors or functional disorders of the brain also often show up in the EEG. In patients in a coma, electroencephalography can provide indications of underlying disorders. EEG is the examination method of first choice, especially in patients with a tendency to epileptic seizures. It can be used, for example, to determine the location from which the seizures originate. In addition, electroencephalography is an indispensable component for diagnosing brain death.
Procedure of the examination
The patient should not have had any stimulating drinks such as coffee, tea or cola beforehand. Freshly washed hair is an advantage. The physician must be informed about which tablets are taken, as some may affect the curve of the EEG. The examination is painless, harmless and can be repeated as often as necessary. About 20 electrodes are placed evenly on the scalp. The routine examination lasts about half an hour at rest with eyes closed. In between, the examinee is asked to open his eyes, close them again and breathe strongly.
In special cases, the examination is performed over 24 hours (long-term EEG, usually with a portable device) or mainly during sleep (sleep EEG), sometimes provocation methods such as sleep deprivation or light flashes are used. This may allow diagnosis of increased convulsiveness. In addition, a video recording may be made during the examination (video-EEG) to see if certain phenomena, such as blinking, are associated with a seizure.
Evaluation of the electroencephalogram
Electrical brain activity depends on what work the brain is doing at any given time. The recorded curves in awake, relaxed people (alpha waves) have a different rhythm than those during mental activity (beta waves), sleep, or illness (delta or theta waves). In addition, the curve pattern looks different in children than in adults.
When evaluating the curve pattern, the physician not only looks at which curves occur, but also whether they are deformed, what frequency they have (i.e. how fast or slow they run) and whether they are regular or form certain patterns. In addition, he examines the curves at the various locations of the lead and can thus obtain indications of a local occurrence (“focal finding”), e.g. a tumor, a circulatory disorder or a hemorrhage.
The decisive factor in the assessment is the overall picture, which is made up of the individual points. Only in rare cases is a change so typical that it points to a specific disease – for example, brain inflammation caused by herpes viruses causes a very specific curve. In case of brain death no brain activity is detectable anymore – therefore only straight lines are shown in the EEG (zero-line EEG). Since the time of death is equated with the irreversible loss of brain function, such a zero-line EEG over 30 minutes is one of the indispensable prerequisites for declaring a patient dead and, for example, removing his organs for transplantation.
