What is an EEG?

An Electroencephaologram (EEG) is a recording of the electrical activity of the brain. The brain produces small electrical signals which can be picked up by an EEG machine and recorded on a computer screen. The EEG is an important part of the evaluation of patients with suspected seizure disorders or brain injury.

What does the EEG show?

The EEG records electrical activity generated by the neurons in the brain, and is sometimes referred to as a "brain wave" test. EEG signals may be normal, or show abnormalities in certain areas. Abnormal EEG signals can be epileptiform activity and may include spikes, spike and wave, and sharp waves. Slow waves on the EEG may be normal or abnormal depending on brain maturation, and patient state. Slowing in the infant may be normal, but in an adult may indicate an abnormality such as encephalopathy.

Epileptiform activity is mostly seen in people with Epilepsy and can take several forms. It may be generalised (recorded over all regions) or focal (recorded in one or more localised regions). Some types of Epilepsy have characteristic epileptiform patterns on the EEG that can lead to a specific diagnosis and treatment.

An abnormal EEG does not necessarily confirm Epilepsy. EEG abnormalities are frequently recorded in children with neurological and behavioural problems (eg. Autism and Cerebral Palsy) and does not signify Epilepsy. Similarly, a normal EEG does not exclude Epilepsy as some types of Epilepsy will show a normal EEG between seizures.

Why have an EEG?

There are a number of reasons why patients are referred for an EEG. Clinical specialists may recommend an EEG for headaches, language delay, learning problems, dizzy spells and behavioural problems. The EEG is primarily used in the evaluation of Epilepsy. It can help distinguish focal from generalised seizures and epilepsies.

Preparing for an EEG

To reduce the amount of natural oils in the hair, it is recommended that the patient thoroughly wash his/her hair the night before the test without conditioner, baby oil, hair gels etc. For the EEG to be successful, the patient needs to be relaxed and remain fairly still during the recording. Young children should have dummies, a bottle and comforters available to them.

What to expect in an EEG

After the Technologist explains the procedure, small non-invasive electrodes are applied to the scalp. The Technologist is required to rub the scalp with a cotton bud to prevent the natural oils from interferring with the EEG signals. The electrodes are held in place by a sticky cream (electrode paste) and sometimes tape which covers the electrode. The test can take up to 60 minutes and includes around 15 minutes to set up. For older children and adults, photic stimulation (flashing strobe lights) and hyperventilation (fast breathing) may induce epileptiform activity or even seizures. The Technologist is unable to comment on the results of the test, as these are provided by the Neurologist in a follow-up appointment.