Electroencephalography (EEG) is a method of medical diagnosis used to measure the summed electrical activity of the brain by recording voltage fluctuations on the surface of the head. It is used to detect and localize pathologic changes in brain electrical activity.
Indications (areas of application)
- Seizure tendency of the brain – epileptic seizures; differential diagnosis of nonconvulsive status epilepticus (NKSE).
- Inflammatory brain diseases
- Bacterial meningoencephalitis (combined inflammation of the brain (encephalitis) and meninges (meningitis)).
- Encephalitis (inflammation of the brain): herpes encephalitis, HIV encephalitis.
- Brain abscess
- Meningitis (meningitis)
- Cerebral malaria
- Endocrine disorders
- Hypothyroid coma caused by severe hypothyroidism (underactive thyroid).
- Addison’s disease (adrenal insufficiency, NNI).
- Cushing’s disease – group of diseases leading to hypercortisolism (hypercortisolism; excess of cortisol).
- Metabolic (metabolic) disorders.
- Hepatic coma (liver failure) caused by severe liver dysfunction
- Uremic coma (renal failure) caused by severe renal dysfunction
- Apoplexy (stroke)
- Delirium
- Dementias (brain degradation processes) – such as Alzheimer’s disease or Creutzfeldt-Jakob disease.
- Brain tumors
- Sleep disorders such as narcolepsy or sleepwalking (somnambulism).
- Pharmacotherapy:
- Treatment with benzodiazepines, clozapine.
- Monitoring of lithium therapy
- Detection of brain death
The procedure
On the scalp, 19 electrodes are placed for clinical EEG derivation according to the internationally used Ten-Twenty system (10-20 system). These are thereby distributed over the scalp at relative distances (10% intervals or 20% intervals) from each other, This allows the voltage differences between each two electrodes to be measured in different combinations. The electrodes are connected via a cable to a recorder, which responds to the electrical impulses. The brain waves are represented in different types of waves. On the basis of the frequency (measurement in Hertz), the amplitude as well as the slope and localization of the brain waves, an assessment of the electrical brain activity can be made. The rhythms are subdivided as follows:
- Alpha activity (8-13/s): main activity in the relaxed state with eyes closed; predominantly parieto-occipital; variability of basic rhythm frequency at most 1.5/s; triggered mainly by thalamic neurons.
- Theta activity (4-8/s); physiologically as singular waves in wakefulness or grouped in subvigilant stages; rhythm generator probably of hippocampus.
- Delta activity (0.5-4/s): predominant EEG rhythm during deep sleep; also associated with learning or reward processing; probably triggered in the cholinergic nuclei of the basal forebrain.
- Sub-delta activity (< 0.5/s): not of importance in routine diagnostics.
- Beta activity (13-30/s): at rest with eyes open and also during sleep; associated with cognitive processes (e.g., computation), emotional arousal, and movement; rhythmicity triggered in part by thalamic neurons.
- Gamma activity (30-100/s): occur with certain cognitive and motor functions; mediates coupling of local neuron populations to larger networks; not of importance in routine diagnostics.
The examination takes approximately 20 to 30 minutes, is harmless, painless, and can be repeated as often as desired. Through electroencephalography, pathological changes in brain activity can be detected and, if necessary, the severity of a disease can be determined.In some cases – such as a seizure disorder (epilepsy) can be localized in the brain, that is, the place where the suffering has its origin, so that under certain circumstances a targeted surgical measure can be initiated.
