Electroencephalogram (EEG)

An electroencephalogram (EEG) is a test that measures the electrical activity in the brain using small metal discs called electrodes attached to the scalp. The brain cells constantly communicate through electrical impulses, recorded as wavy lines on the EEG.

Who conducts EEG?

An EEG is performed by a neurologist or a specially trained technician under the supervision of a neurologist. EEG is typically conducted in medical imaging centers, hospitals (neurology departments), specialized epilepsy centers, or Neurology clinics.

Why is an EEG performed?

An electroencephalogram (EEG) is performed for various reasons to evaluate and diagnose conditions related to brain activity.

  • When epilepsy is present, seizure activity will appear as rapid spiking waves on the EEG.
  • Individuals with brain lesions, which can result from tumors or strokes, may exhibit abnormally slow EEG waves, depending on the size and location of the lesion.
  • Furthermore, the EEG can aid in diagnosing other conditions that affect brain activity, including Alzheimer’s disease, certain psychoses, and the sleep disorder called narcolepsy.
  • The EEG can also provide insights into overall brain electrical activity, making it helpful in assessing trauma, drug intoxication, and brain damage in comatose patients and monitoring blood flow during surgeries.

What are the different types of EEG?

  • Routine EEG: This is the most common type of EEG and takes 23 minutes. The EEG technologist may instruct the patient to modify breathing patterns or focus on flashing lights.
  • Prolonged EEG: A prolonged EEG test that lasts several days provides more detailed information than a routine EEG. The doctors commonly use it to diagnose and manage seizure disorders.
  • Sleep EEG: This EEG is performed while the patient is asleep. It helps evaluate sleep-related disorders and assess brain activity during different sleep stages.
  • Ambulatory EEG: This test involves wearing a portable EEG recorder for an extended period, usually 1 to 3 days. It allows for more prolonged monitoring to capture infrequent or episodic events.
  • Video EEG: This combines video recording with EEG monitoring. It captures visual and electrical information, comprehensively assessing brain activity during seizures or other events.

How is EEG performed?

Before EEG

  • Washing hair, the night before the test is recommended, without using any conditioner or styling products afterward.
  • Avoid consuming caffeine-containing foods and drinks, such as coffee, black tea, or energy drinks, for eight hours before the test.
  • Make sure to follow the doctor’s instructions, including any changes to medication.

During EEG

  • The patient will lie in a comfortable bed while a technician applies approximately 23 electrodes to the scalp using glue or paste.
  • The patient can relax with the eyes open or closed.
  • The patient may look at a bright light or change the breathing pattern to observe any brain changes.
  • If the patient experiences a seizure during the test, the technician will note it.
  • For routine EEGs, the recording typically lasts for 23 minutes, with an effort to capture a portion of drowsiness or sleep. In longer EEGs, the goal is to obtain a longer sleep recording, usually lasting one hour and 15 minutes.
  • In the case of an ambulatory EEG, the patient can go home and carry or wear a portable EEG recorder for one to three days while going about normal activities.

If the patient did not receive a sedative, there should be no side effects, and they can resume their routine. If a sedative is used, the medication may take some time to wear off.

After the EEG, the technician will remove the electrodes and clean the scalp, which may make hair and skin sticky. It is recommended to wash hair at home to remove any residue.

An EEG is a safe and painless test that measures brain activity. It is used to help doctors determine the cause of symptoms such as seizures, confusion, or memory loss. The doctors can provide appropriate treatment and management strategies for brain-related conditions by diagnosing the underlying condition.


  1. Mayo Clinic. EEG (electroencephalogram) Available from: https://www.mayoclinic.org/tests-procedures/eeg/about/pac-20393875
  2. Cleveland Clinic. Electroencephalogram (EEG) Available from: https://my.clevelandclinic.org/health/diagnostics/9656-electroencephalogram-eeg
  3. Electroencephalogram (EEG). Available from: https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/electroencephalogram-eeg

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