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How to Prepare / Test Overview

Electroencephalography (EEG)

Test Overview
Electroencephalography (EEG) records the electrical activity on the brain’s surface. Sensors are attached with paste to your head and connected by wires to a computer. The computer records your brain’s electrical activity on the screen as wavy lines. Certain brain abnormalities can be detected by observing changes in the normal pattern of the brain’s electrical activity.

Why It Is Done
Electroencephalography (EEG) may be done to:

  • Help establish a diagnosis of epilepsy and determine what type of seizures a person with epilepsy is having. EEG is the most useful and important test in confirming a diagnosis of epilepsy.
  • Identify the location of a suspected brain tumor and the potential damage caused by it, inflammation, infection (such as encephalitis), or disease in the brain.
  • Evaluate periods of unconsciousness or dementia.
  • Help predict a person’s chance of recovery after cardiac arrest or other major trauma.
  • Study sleep disorders.

How To Prepare
Avoid foods that contain caffeine (such as coffee, tea, cola, and chocolate) for at least 8 hours before the test. Eat a small meal shortly before the test, because low blood sugar (hypoglycemia) may produce an abnormal test.

Since the electrodes are attached to your scalp, it is important that your hair be clean and free of sprays, oils, creams, lotions, and other hair preparations.  No braids please.

To detect certain types of abnormal electrical activity in the brain, you may have to be asleep during the recording. As a result, you may be asked not to sleep at all the night before the test or to reduce your sleep time to 4 or 5 hours by going to bed later and getting up earlier than usual. If you know that you are going to have a sleep-deprived EEG, plan to have someone drive you to and from the test.

How It Is Done
The technologist will attach 24 flat metal discs (electrodes) to different places on your head and on your chest, using a sticky paste to hold the electrodes in place.

The electrodes are connected by wires to a machine that amplifies and records the electrical activity inside the brain. The machine records the electrical activity as a series of wavy lines.

You will be asked to lie on your back on an examining table. Try to lie still, with your eyes closed during the recording, and do not talk to the technologist unless you need to. The technologist will observe you directly during the test.

In addition to the recording of your brain’s electrical activity while you are resting, certain procedures may be done to observe how your brain responds to different forms of stimulation:

  • You may be asked to breathe deeply and rapidly (hyperventilate) for several minutes.
  • You may be asked to look at a bright, flashing light called a strobe. This is called photic stimulation.
  • You may be asked to go to sleep.

An EEG usually takes 1 hour. After the test you may resume normal activities. However, if you were sleep-deprived, you may want someone to drive you home after the test.

How It Feels
An EEG is a painless test. You will not feel anything out of the ordinary during the EEG recording.
Paste is used to position the electrodes; some paste may remain in your hair after the test, so you will have to wash your hair when you get home to remove it. You might want to bring a hat or scarf to cover your head until you get home.
If you are asked to breathe rapidly, you may feel lightheaded or have some numbness/tingling in your fingers or face. This reaction is normal. It will go away within a few minutes after you start breathing normally again.

Electroencephalography (EEG) is a very safe test. The electrical discharges produced by your brain are recorded, but at no time is any electrical current put into your body. An EEG should not be confused with electroshock (electroconvulsive) therapy.
If you have a seizure disorder such as epilepsy, a seizure may be triggered by the flashing lights or by hyperventilation. If this occurs, the technologist is trained in how to take care of you during the seizure.

What Affects the Test

  • Excess movement of the head, body, eyes, or tongue may make electroencephalography (EEG) test results difficult to interpret.
  • Inability to cooperate and remain still throughout the test may interfere with EEG results. .
  • Hair that is dirty, oily, or covered with hairspray or other hair preparations can interfere with the placement of the electrodes.

Electromyography and Nerve Conduction Velocity (EMG/NCV) Info and Prep Sheet

NCV (Nerve Conduction Velocity) is a test of the speed of conduction of impulses through a nerve. The impulse may feel like an electrical shock and the patient will feel it to varying degrees. It may be uncomfortable to some patients (though only during the actual test and there should be no residual pain once the test is finished).

EMG (electromyography) is a test that measures muscle response to nervous stimulation (electrical activity within muscle fibers). Often the nerve conduction test is followed by an EMG which involves a needle electrode being inserted through the skin into the muscle and the patient being asked to contract and relax that muscle. This can be uncomfortable during the test and muscle soreness at the site of the needle may be experienced subsequently as well. These needles are not hollowed and are thinner than the type of needle used to draw blood.


  • No lotions or oils on the skin of areas to be tested (i.e. arms or legs)
  • Clean, dry skin
  • If having study on lower extremities – wear shorts or you may want to bring a pair of shorts to change into
  • If having study on upper extremities – wear short sleeve shirt
  • No heavy perfumes of colognes

Somatosensory Evoked Potentials

What is an evoked potentials study?
Evoked potentials studies measure electrical activity in the brain in response to stimulation of sight, sound, or touch. Stimuli delivered to the brain through each of these senses evoke minute electrical signals. These signals travel along the nerves and through the spinal cord to specific regions of the brain and are picked up by electrodes, amplified, and displayed for a doctor to interpret.

Somatosensory evoked response (SSEP) test. This test can detect problems with the spinal cord as well as numbness and weakness of the extremities. For this test, electrodes are attached to your wrist, the back of your knee, or other locations. A mild electrical stimulus is applied through the electrodes. Electrodes on your scalp then determine the amount of time it takes for the current to travel along the nerves to the brain.


  • No lotions or oils on the skin of areas to be tested (i.e. arms or legs)
  • Clean, dry skin
  • If having study on lower extremities – wear shorts or you may want to bring a pair of shorts to change into
  • If having study on upper extremities – wear short sleeve shirt
  • No heavy perfumes of colognes
  • Wash your hair the night before the test, but do not use conditioner or apply any hairspray or other hair products.

Skin Biopsy

To diagnose small fiber neuopathy by means of skin biopsy. This is a simple procedure in which a small circular piece of skin (a punch biopsy, smaller than the diameter of a pencil eraser) is taken from the surface of the skin. Lidocaine, a local anesthetic, is used to numb the skin first. A band-aid is placed over the biopsy site, no stitches are involved, and it heals by simply scabbing over. The whole procedure takes only a few minutes. The skin specimen is processed and sent to a lab so the small nerve fibers in the skin can be visualized and qualified by specialists.


  • No lotions or oils on the skin of areas to be tested (legs)
  • Clean, dry skin
  • Wear shorts or you may want to bring a pair of shorts to change into
  • No heavy perfumes of colognes

Home Sleep Study

There is no preparation for this. You will need to fill out the paperwork titled Home Sleep Study paperwork that can be found under   Patient Paperwork    and watch the video below. 


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