Neurophysiological testing
Electroencephalography
What is an EEG ?
An electroencephalograph (EEG) is a prescribed procedure which uses electrodes attached to the scalp to measure the electrical activity of the brain..
For what reason would an electroencephalogram be prescribed?
In spite of recent developments in neuroimaging (CT scanner, MRI), EEGs remain one of the only available dynamic procedures for the analysis of brain activity. It is mostly used to detect epilepsy. Inter-critical EEG (completed outside of attacks), sometimes rendered more sensitive through sleep deprivation, provides diagnostic arguments for the clinical diagnosis of suspected epilepsy cases and the classification of attacks and epileptic syndromes. EEGs are useful for the aetiological diagnosis of malaise, confusions and comas, the detection of medication overdosing, encephalopathy or encephalitis or a non-convulsive epileptic condition. An EEG is also one of the legal tests required to provide evidence of brain death.
Does the test require any specific preparation?
No particular preparation is necessary before an electroencephalography. However your hair should be clean, dry and free of hair-gel or lacquer. You can eat and drink normally and it is important to continue any medication as normal. In most cases you can make your own way to the electroencephalography laboratory for the test. If you are hospitalised the EEG technician will come to your bedside to make the recording.
Potential risks :
EEG presents no risks whatsoever.
The test procedure
The electroencephalography test is organised over two phases::
- The preparatory phase
You will be lying down or seated with a cushion placed under the nape of your neck. A salt and pumice paste will be applied to your scalp. Electrodes (moistened pads) will be attached to your head using a flexible rubber helmet. The electrodes are then connected by wires to a recording device. Two adhesive electrodes will be placed on your torso to record your heart rate. This phase takes around 15 minutes to complete.
- The recording phase
The electrical signals generated by your brain will be recorded by a computer. Your eyes will be closed during most of the test. Certain activation tests will be completed (opening and closing the eyes, breathing deeply, reaction to bright light from a torch). For “siesta” EEGs recordings of sleep levels will also be taken. The standard EEG recording phase takes about 30 minutes and the “siesta” EEG takes about 60 minutes.
Practical information
Dr Christine BEAUD, Neurophysiologist, in charge of the Electroencephalography Laboratory, Hospital Physician of the Physiology-Functional Testing Unit of the Louis Mourier Hospital in Colombes.
Data collection:
- Philippe GREBET, EEG technician
Since 2016, electroencephalography is reserved for Patients hospitalised at HFB only.