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Electroencephalogram (EEG) Definition

An electroencephalogram or EEG is a visual record of the brain’s electrical activity.[1]https://medical-dictionary.thefreedictionary.com/EEG[2]https://www.nhs.uk/conditions/electroencephalogram[3]https://pubmed.ncbi.nlm.nih.gov/20578033/ 

Physicians and researchers attach small metal discs (or electrodes) to the scalp to record the electrical impulses that spark between brain cells. 

This activity creates a report that looks like wavy lines on a screen, allowing physicians to study brain disorders and abnormalities.

Once electrodes are in place, an EEG can take up to 60 minutes. However, testing for certain sleep-related conditions can take longer. Ambulatory EEGs (aEEGs) are rare but can record brain activity over several days.

Electroencephalograms can help diagnose brain disorders such as:[4]https://medical-dictionary.thefreedictionary.com/EEG[5]https://www.nhs.uk/conditions/electroencephalogram

  • Epilepsy
  • Seizure disorders
  • Brain tumors
  • Traumatic brain injury
  • Brain dysfunction from a variety of causes (encephalopathy)
  • Inflammation of the brain (encephalitis)
  • Stroke
  • Sleep disorders

Other functions of EEGs include:

  • Monitoring blood flow in the brain during surgical procedures
  • Evaluating the extent of trauma or drug intoxication in comatose patients
  • Finding the right level of anesthesia for someone in a medically-induced coma
  • Confirm brain death 

While an EEG is only reading brain activity, other seemingly unrelated factors can interfere with the test, including: 

  • Low blood sugar (hypoglycemia)
  • Body or eye movement during the tests
  • Bright or flashing lights
  • Sedatives and similar medicine
  • Caffeine, including coffee, cola, tea, or energy drinks
  • Oily hair or hair products

Possible Risks and Side Effects

EEGs are safe, painless, and the electrodes don’t transmit any physical sensations during the procedure. There are no known side effects, except in rare cases when EEGs trigger seizures, usually in those with epilepsy. Most patients can return to their regular routines directly after the procedure.