What is an EEG?

EEG stands for electroencephalogram. It is the recording of the “brainwaves” – the electrical activity of the brain. Patients are referred for an EEG for a variety of reasons including fits, faints and blackouts and the results may assist the referring doctor in diagnosis and treatment.

Before the EEG

  • Please ensure that your hair is clean. Do not use any hair products (gel, hair spray etc.).

  • Please have meals as normal.

  • Take your medication as normal unless otherwise directed.

  • Please bring a list of any medication you may be taking.

Having the EEG

The EEG appointment will be 60-90 minutes. The EEG technologist will make measurements of your head then after gently rubbing over the marks, attaches approximately 23 electrodes (small metal discs) using a sticky paste. You will either be sat in a chair or lying down during the recording and the physiologist will ask you to open and close your eyes at various times. We will also video record you (with your consent) whilst the EEG is being performed.

The following will be needed during your test:

  • Deep-breathing. This may produce changes in your brain activity that could help in diagnosis. You will be asked to take deep breaths for about 3 minutes. This may cause you to feel light-headed or experience tingling in the fingers – this is a normal response and will settle when your breathing returns to normal.

  • Photic stimulation. This is an important part of the test for people who may have seizures or blackouts caused by flashing lights. You will be asked to look at a bright flashing light with your eyes open and closed. This may very rarely cause a seizure in people that are sensitive but the Clinical Physiologist who monitors the EEG will stop if you appear sensitive.

What are the side-effects of the test?

There are no side effects of the test at all. We cannot read your mind or thoughts or emotions you may have. No electricity or needles are used – we only record signals produced naturally. This is an investigation and NOT a treatment. There is no danger to pregnant ladies or their unborn babies from this test.

What happens after the test?

The results of the investigation need to be analysed afterwards and a full report will be sent to the doctor who referred you for the test. The results will not be available to you on the same day.


Nerve conduction studies and Electromyography

NCS procedure Explained

During the test, your nerve is stimulated, usually with electrode patches attached to your skin. Two electrodes are placed on the skin over your nerve. One electrode stimulates your nerve with a very mild electrical impulse. The other electrode records it. The resulting electrical activity is recorded by another electrode. This is repeated for each nerve being tested.The speed is then calculated by measuring the distance between electrodes and the time it takes for electrical impulses to travel between electrodes. The voltage of the electrical pulses used during an NCV is considered very low.

What is an EMG?

A related test that may be done is an electromyography (EMG). This measures the electrical activity in your muscles. It is often done at the same time as an NCS. Both tests help find the presence, location, and extent of diseases that damage the nerves and muscles.

The tests are typically carried out for conditions like carpal tunnel syndrome, ulnar neuropathy, peripheral neuropathies and radiculopathies.


There is no specific preparation for the procedure. Dress in clothes that allow access to the area to be tested. Please do not use lotions or oils on your skin on the day of the procedure.