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EEG for Adults – Routine

Updated 23 February 2021

EEG measures the natural electrical activity of the brain via about 22 scalp electrodes. This electrical activity is sometimes referred to as 'brainwaves'. It is useful in a range of neurological conditions and is most commonly used in the investigation and assessment of epilepsy.

Firstly, the head is measured and marked with the electrode positions. Then the patient can sit or lie on a comfortable couch while leads are attached using conductive cream. Leads from the electrodes connect to the EEG computer. Also, there are usually two more on the arms or shoulders to monitor the heart rate. 

An EEG recording usually lasts about 20 minutes and the patient does not feel anything while it is happening. The patient is asked to open and close their eyes several times to evaluate accompanying changes in brainwaves. The rest of the test time is spent with eyes closed to encourage relaxation and, if we are fortunate, a period of sleep. The patient should try to keep still and relax during recording as body movement can make it difficult to interpret results. Afterwards, electrodes and cream are wiped off and the patient can tidy their hair although they will probably need a hair wash later to remove any residue. 

A video of the test is always made, to record any coincidental attacks or symptoms that a patient may have during their test. Only sections of video of diagnostic value are retained with the EEG file and the rest is deleted. 

For some EEGs, activation is also included to show more EEG activity that might help in the diagnosis. Activation is achieved by asking the patient to do several minutes' deep breathing (hyperventilation) and, later, to watch a flashing light (intermittent photic stimulation). The criteria used to decide upon appropriate activation for each individual patient, includes ability to co-operate, physical condition, age and the condition under investigation. Because of the extremely small risk of provoking an epileptic seizure in susceptible people, consent to activation is required before recording begins. 

Currently, non-urgent EEGs are reported once a week, so results may take at least two weeks to arrive with the referring clinician.

Click on the following links to find out more about what epilepsy is, and the diagnosis and treatment of epilepsy.