 |
| |
NEUROPHYSIOLOGY
EEG
What is an EEG?
What can I expect during an EEG?
Does an EEG have any after effects?
Is any special preparation needed beforehand?
What is an EEG?
EEG stands for electroencephalogram. It is a recording of the 'brainwaves' - the electrical activity of the brain.
The many nerve cells that make up the brain produce continuous electrical activity when a person is awake, asleep or even in a coma. This can be recorded using small metal discs called electrodes, which are placed on the scalp. The electrical signals are then amplified by specialised equipment to produce what is seen in the EEG tracing (see figure 2 in printed bound version or pdf).
The signals show up on the EEG tracing as wavy lines, representing the fluctuations in electrical activity from moment to moment. Doctors can gain a great deal of information about the workings of the brain by examining these tracings.
What can I expect during an EEG?
After the EEG technician has asked you a few questions about your medical history, he or she will explain what will happen during the test. The whole procedure normally takes one to one-and-a-half hours, with the recording itself usually running for about 30-45 minutes. The EEG is carried out either with you sitting up in a comfortable chair or lying on a couch.
The first step is to apply the electrodes - usually about 20 in all - to the scalp. These are placed in standard positions, according to an internationally agreed convention. The technician will begin by measuring around the head with a tape measure to determine the position for each electrode, which he or she will mark with a skin pencil.
The skin where each electrode is to be placed will be cleansed to ensure that the electrical contact is good enough to allow the weak signals from the brain to be recorded properly. You will usually find that your appointment letter asks you to come for your EEG with 'clean, dry hair'. This is not meant to be insulting. The request is made because hair products and even the hair's natural oils can make it difficult for the technician to get a good electrode contact with the scalp.
The electrodes, which are like little cup-shaped discs, are usually stuck in place with a special paste which also helps to conduct the electrical signals. Some of them may have a special conducting jelly put in them before they are stuck onto the scalp. The technicians are very skilled at doing this and it is not uncomfortable. When everything is ready, the technician will ask you to sit or lie in as relaxed a state as you can. This can be quite difficult if you're feeling nervous in unfamiliar surroundings, but once the test is underway, people usually find that they are gradually able to settle down. It is quite important to relax, since a tense person will have tense muscles around the face and forehead and these will produce electrical signals of their own. The electrodes on the scalp will then pick these signals up too, and they will obscure the EEG and make the recording less useful.
During the recording, you will be encouraged to close your eyes, relax and drowse, since this may give more information than if the recording takes place when you are fully awake. Despite being in strange surroundings, people often drop off to sleep during an EEG.
Does an EEG have any after effects?
A routine EEG is a straightforward test and there are no after effects. After the test you can go home or back to work and carry on as usual.
Is any special preparation needed beforehand?
No, and you should continue with any anti-epilepsy treatment or other drugs which you have been prescribed unless your doctor tells you otherwise.
| |
 |
|
|
| |
 |
|
