What Is an Electroencephalogram Used For?

what is an EEG for
An EEG is a test used to detect abnormalities in brain waves or the electrical activity of your brain.

An electroencephalogram (EEG) is a test in which doctors place special electrodes over the scalp to measure electrical activity in your brain and record brain wave patterns. These waves arise out of voltage fluctuations in the cell membranes of the cortical neurons (brain cells). Certain brain conditions affect these brain wave patterns and, thus, can be diagnosed using an EEG.

Conditions that can be diagnosed using an EEG include:

  • Epilepsy: The person will show typical wave patterns during seizures. Not only can an EEG confirm epilepsy, based on various EEG patterns, but also doctors can classify the condition as grand mal type, petit mal type, focal epilepsy or absence seizures.
  • Sleep disorders: Various sleep disorders such as narcolepsy (sleep paralysis), somnambulism (sleepwalking) and periodic limb movement disorder can be diagnosed using an EEG.
  • Brain conditions: Miscellaneous conditions such as a brain tumor and brain injury may be diagnosed using an EEG. It can also help distinguish epileptic seizures from syncope (fainting spells), migraine and psychogenic disorders.
  • Brain death: EEG wave patterns may be used in some cases to record brain death.
  • During anesthesia and brain surgeries: An EEG is often used to gauge the depth of anesthesia during brain surgeries. Similarly, an EEG recording during brain surgery may guide the surgeon to perform the particular procedure.
  • Sleep studies: These are often conducted to diagnose sleep disorders such as unexplained insomnia and sleep apnea syndrome or in a comatose person.

An EEG only guides the doctor about electrical activity in your brain. It cannot read your thoughts or feelings.

How do I prepare for an electroencephalogram (EEG)?

Your doctor will instruct you accordingly and may ask you to avoid caffeine-containing drinks 24 hours before your EEG. They will advise you regarding your existing medications and their doses. Sometimes, they may ask you to stay awake the night before so that they may perform a “sleep deprivation electroencephalogram (EEG).” Wash your hair the night before your EEG with water and shampoo, however, do not use any hair oil or conditioner.

An EEG session may take anywhere from two to four hours depending on your condition. The EEG technician takes measurements of your head, applies a special cream to your scalp and sticks disc-like electrodes all over your head. These electrodes are connected to the EEG machine through wires.

The machine records your brain wave patterns over the next few hours as you relax, breathe deeply and try to sleep, as well as while you are awake. The technician will ask you to perform actions, such as open/close your eyes, breathe deeply for three minutes, etc. Sometimes, you have to look at bright flashing lights and blink.

After the test, the technician will remove the electrodes using warm water, and you will probably need to wash your hair when you get home. You can go home immediately, but do not drive yourself if you were given sedatives during the procedure. Your results will be pooled and interpreted within a week or two. A full report will be sent to your doctor who will then discuss it with you.

Which is better, an EEG or MRI?

Both magnetic resonance imaging (MRI) and electroencephalogram (EEG) help investigate brain conditions.

An MRI, in general, can help the doctor localize lesions/abnormalities in the brain and detect cortical and deeper lesions. While an MRI scan is good at telling doctors where the lesions are, an EEG is good at detecting only physiological (functional) cortical abnormalities in the brain.

One disadvantage of an EEG is difficulty figuring out the exact part of the brain where the abnormal brain wave activity starts. This is because lots of electrodes are attached all over your scalp (64 or 128). However, both tests have their distinct merits.

Does an EEG have side effects?

An electroencephalogram (EEG) is generally a painless and safe procedure. In rare instances, EEG maneuvers such as exposure to blinking lights or breathing exercises may precipitate seizures in a person with a seizure disorder. This will be immediately treated by the doctor present. Some people may feel sleepy after the test due to sleep deprivation or sedatives used during the procedure.

Other than that, an EEG is painless and does not cause any discomfort.


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