What is an electroencephalogram?

An electroencephalogram (EEG) is a diagnostic test that measures brain electrical activity through electrodes placed on the scalp. The results are reproduced on a screen in the form of a series of waves.


What is the purpose of an electroencephalogram?

The electroencephalogram is used primarily for the diagnosis and monitoring of epilepsy. It is often prescribed to patients suffering from cancer, because both the primary tumors of the brain and any brain metastases caused by cancers of other organs can cause epilepsy. It is also recommended in the presence of a potential inflammation of the nervous system and to diagnose sleep disorders. Finally, it can be useful as a complementary examination in case of headaches, head trauma and other neurological diseases.


Which patients can undergo the exam?

Any person at any age can undergo an EEG exam.


How is the EEG performed?

The patient sits on a chair or bed to promote relaxation and the electrodes are placed on the scalp. In some cases, the electrodes are placed on an elastic headphone. A conductive gel is applied on the electrodes through a syringe with a blunt needle in order to achieve appropriate positioning of the electrodes. It is mandatory to remain relaxed and still to optimize the recording of the electrical signal of the brain and reduce movement and muscular artefacts. The continuous fluctuation of normal brain activity between the various points of the scalp provides small differences in electrical potential (millionths of a volt, microvolts), which are amplified and recorded normally for several minutes (in special cases up to 24 hours). In this way each electrode is measured in terms of variations of voltage in time. Normally, the electrodes are placed according to a fixed pattern (system 10-20) on all parts of the scalp. Since each electrode reflects in the forefront of the activities of the brain, the EEG is able to provide information not only on abnormal electrical activity, but also on the location of the abnormalities.





Preparation standards

It is required that the patients wash their hair without using gels or lacquers on the day before the exam. On the day of the exam, a normal breakfast meal is allowed and the patient should take the usual therapies unless otherwise instructed by a doctor. In the case where EEG serves to analyse brain activity during sleep, the patient is required to stay awake the previous night to help induce sleep at the time of the exam. The patient is also required to bring a doctor’s prescription for the exam and all relevant necessary documentation.


Is the EEG painful and/or dangerous?

The exam is neither painful nor dangerous. The only discomfort may be caused by the requirement to remain still with the eyes closed during the exam and attempting to relax all the muscles. Additionally, during the application of the electrodes a slight pulling of the hair may occur. People with epilepsy rarely experience an attack, which can be triggered by the lights used to check the patient’s eyes. Occasionally, the gel applied to the electrodes may cause slight skin irritation.