How is it performed? of EEG

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Around 20 electrodes (small metal discs) usually silver coated are attached to the scalp and kept in good electrical contact using conductive electrode jelly in specific positions. The person will usually be lying down or sitting relaxed in a chair.

Brain electrical activity is usually recorded for 10 to 30 minutes, but can be done for an hour or more to get more information.

Most people will be asked to close their eyes but will often be asked to open them for short periods. Also they will be asked to carry out a period of deep breathing (hyperventilation) for approximately 3 minutes.

At the end of the recording, the person is often shown a light that flashes at different rates. This is done to test the reactivity of the brain to the light. Some people who are sensitive to flashing lights may show abnormal activity in the EEG. In specific and extreme conditions, flickering lights may provoke seizures.

Often simultaneous video monitoring may be done during the EEG recording, so other activity can be very closely correlated to the EEG tracing. Video monitoring is always used for Long Term Monitoring recording. The person may also have an event button connected to the EEG machine so that times when the patient thought they were having an epileptic attack can be easily identified.

The use of EEGs to test sleep disorders is usually done at a sleep centre, but can also take place either in the patientâ€™s home or during an overnight stay in hospital. The tracing is taken together with heart rate, airflow, respiration, oxygen saturation and limb movement. When there is a period of apnoea (the person stops breathing) this is correlated with the stage of sleep it occurred as shown by the EEG recording.