Electroencephalography (EEG)

Elektroencephalographie Eeg Neurozentrum Aarau

What is an electroencephalogram (EEG)?

EEG is a method for measuring electrical brainwaves that makes it possible to record natural voltage fluctuations in the cerebral cortex.

How does EEG work?

Metal lamellas are placed on the scalp (usually 21 electrodes). The electrical voltage differences are measured between various combinations of two electrodes, then amplified with a special device and finally recorded in the form of brainwaves. This electrical voltage is generated by the nerve cells themselves and reflects their activity and how well they are functioning.

The doctor will assess the brainwaves based on their frequency, amplitude, slope and location on the surface of the brain. The symmetry between the two sides of the brain is also important.

What is the purpose of an EEG?

An EEG is used to record pathological changes in electrical brain activity. These include:

  • Potentials typical of epilepsy: These are EEG changes that commonly occur in people with a tendency towards epileptic seizures (spasmophilia of the brain). The EEG can help to diagnose epilepsy. However, the EEG often does not reveal any abnormalities between seizures, which is why it may be necessary to carry out tests several times and under conditions that increase the likelihood of a seizure (e.g. sleep deprivation during the night before the examination).
  • General changes in EEG results: These changes affect the entire cerebral cortex and can, for example, occur in cases of brain inflammation (encephalitis) or metabolic brain disorders or poisoning. The results may provide indications of the severity of the disorder.
  • Focal lesions: These are regional changes in brainwaves that occur mainly in the case of localized brain disorders, such as strokes, tumors or local inflammatory processes.

EEG is currently the most commonly used diagnostic method when there is a suspicion of epileptic phenomena.

What is the EEG procedure?

In most cases, 21 electrodes are placed equidistance from each other on the patient’s scalp to record brain waves. To keep them from slipping, the electrodes are attached to a hood that encloses the forehead and part of the head with hair, similar to a hairnet.

A routine EEG reading takes about 30 minutes. After the reading is taken in an idle state with closed eyes, sometimes a flickering light test is carried out as well. The patient looks into a rapidly blinking bright light (stroboscope) to reveal any previously hidden epileptic disposition. In special cases, an EEG test will have to be carried out over a 24-hour period. The EEG examination is harmless, painless and can be repeated as many times as needed.