An electroencephalogram (EEG) is a procedure used to monitor the electrical activity in the brain. The brain cells communicate with each other via electrical impulses. This test can be helpful to determine any serious disorders related to brain function. The EEG test tracks and records brain wave patterns. Small metal discs called electrodes are placed on the scalp with wires. The electrodes study the electrical impulses in the brain and send signals to a computer that records the results.

The electrical impulses in an EEG recording look like wavy lines with ups and downs. These lines let healthcare professionals determine whether there are any abnormal patterns. Any abnormalities may be a sign of seizures or other brain disorders.
Woman undergoing electroencephalogram (EEG)

Why Is An EEG Performed?

This test has been used as a vital tool since 1929 to identify problems in the electrical activity of the brain that are related to certain brain dysfunctions. The readings given EEG are used to either confirm or rule out several health conditions, including:

  • Seizure disorders
  • Head injury
  • Encephalitis
  • Brain Tumour
  • Encephalopathy
  • Sleep Disorders
  • Stroke
  • Dementia

Further, this procedure is done for a person in a coma stage to assess their level of brain function. Also, the test is used to determine the activity while doing brain surgery.

Also Read: Brain Atrophy: Symptoms, Causes And Treatment


This test is painless and safe, however, if an EEG does not show any abnormalities, stimuli like strobe lights, or rapid breathing may be included to help induce any abnormalities.

In a person with epilepsy or another seizure disorder, there’s a minimal risk that the stimuli presented during the test like a flashing light may cause a seizure. The technician performing the EEG test is well trained to safely manage any situation that might develop during the procedure.

Hyperventilation is commonly stimulated during an EEG to produce abnormalities. Also, a few patients may not be able to hyperventilate safely, such as people with a history of stroke, asthma, or sickle cell anaemia.

Also Read: Dementia: Causes, Symptoms and Treatment

Factors That Interfere With An EEG Reading

Several kinds of movements can highly cause artefacts on EEG recording that mimic brain waves. These movements are considered by the technician which includes:

  • Pulse and heartbeat
  • Breathing
  • Sweating
  • Mouth movements
  • Muscle movements

Some of the other factors that can influence EEG reading include:

  • Low blood sugar
  • Bright or flashing lights
  • Medications, such as sedatives
  • Caffeine intake
  • Oily hair

How To Prepare For The Test ?

Some of the steps to be followed before taking the test include:

Check with your doctor if you need to stop taking any medications before the test. Also, give a list of medications taken by the patient to the technician performing the EEG.

Wash hair thoroughly with shampoo the night before the test. Don’t apply any products like gel or sprays on the day of the test.

Avoid drinking or consuming any food containing caffeine for at least 8 hours before the test.

The doctor may ask the patient to sleep as little as possible the night before the test, so that patient can sleep during the EEG. Also, the patient may be given a sedative to help relax and sleep before the test starts.

What To Expect During An EEG?

An EEG determines the electrical impulses in the brain with help of electrodes attached to the scalp. An electrode is a conductor via which an electric current enters or leaves. The electrodes transfer information from the brain to a machine that evaluates and records the data. The tests generally take about 30 to 60 minutes to complete and involve the following steps:

The person will be made to lie down on the back in a bed or reclining chair

A technician will take a measurement of the person’s head and mark where to place the electrodes. These regions are scrubbed with a specific cream which helps the electrodes get a high-quality reading.

The technician will apply a sticky gel-type adhesive on 16 to 25 electrodes and attach them to spots on the scalp.

Once the test starts, the electrodes send electrical impulses data from the brain to the recording machine. This machine converts electrical impulses onto visual patterns that appear on a screen and the computer saves these patterns.

The technician may instruct the person to do certain things while the test is in progress such as to lie still, close eyes, breathe deeply, or look at stimuli.

During the procedure, very little current passes between the electrodes and the skin, so the person may feel very little to no discomfort.

In a few cases, a person may undergo a 24-hour EEG, where the video is used to capture seizure activity. The EEG may show abnormalities even if the seizure does not develop during the test. But it does not reveal any past abnormalities associated with seizures.

After The Procedure

The technician will remove the electrodes from the scalp after the test is done. The person may continue with regular work. However, if the person was given a sedative, then the drug will remain in the system for a while. Thus, the person may need some help to take them back home after the test. Also, the person should take a rest and avoid driving until the medication wears off.

What Does Results Mean?

Normal Results

Electrical activity in the brain looks in an EEG as a pattern of waves. Different levels of consciousness like sleeping and walking have a particular range of frequencies of waves per second that are normal. For instance, the wave patterns move faster when a person is awake than at rest or asleep. This test will show if the frequency of the wave patterns is normal.

Abnormal results may be due to the following health problems

  • Epilepsy or another seizure disorder
  • Abnormal bleeding or haemorrhage
  • sleep disorder
  • Encephalitis
  • Tumour
  • Dead tissue due to a blockage of blood flow
  • Migraine
  • Excessive alcohol or drug use
  • Head injury

A neurologist interprets the recordings from the EEG and then sends the results to your doctor. It’s essential to discuss and understand test results with the doctor and plan treatment accordingly.