Electroencephalography (EEG) is a diagnostic technique where the electrical activity of the brain is recorded  using either scalp surface electrodes or more invasive direct brain recording electrodes. Most departments use digital recorders allowing many channels of data to be recorded in real time, stored electronically and available for off line reanalysis and reporting.The recordings are made by specially trained technicians (Clinical Physiologists (Neurophysiology))who make an initial technical examination and report of the record.

Reporting is then carried out by a Consultant Neurophysiologists or a member of the junior medical staff under supervision who interpret the technical data in the light of the clinical history and/or clinical examination and produce the final report.

Techniques List

1. Standard recording

    After electrode application, a 40-60 minute resting recording is made. Then a number of activation procedures such as hyperventilation and photic stimulation are carried out , if clinically indicated.

2. Sleep Deprived Recording

The patient is instructed to refrain from sleep for 24 hours, and then a standard recording is made. During this the patient is encouraged to fall asleep. The period immediately prior to sleep is particularly useful in the diagnosis of epileptic disorders.

3. Video EEG

This technique is used with patients in whom a non-epileptic seizure disorder is suspected. Following an interview,  a recording is made in the presence of a member of the medical staff . We try to ascertain and reproduce the circumstances in which a typical attack would occur. A video recording of the patient is made at the same time as the EEG, and if an attack occurs, (with the patient's permission) this is shown to any member  of the patient's family or a friend who has witnessed a previous attack to ensure that it is typical. Correlation of the attack characteristics and the EEG may be diagnostic.

4. Ambulatory Recording

A limited number of EEG electrodes are attached to the scalp as in a routine recording. The patient is then connected to either a small portable tape recorded or a digital recorder. They are then able to carry out a normal day's activities whilst the recording is being made. The recorder is then connected to a central system and the recording downloaded for analysis. Uninterrupted recordings over 24 hours are made this way.

5. Video Telemetry

This technique involves long term (1-5 days) synchronous recordings of the patient's EEG and a Video of their  activities so that any behavioural disturbance may be correlated with the EEG. It is used both for diagnosis in clinically comlex cases as well as in preparation for epilepsy surgery.

6. Depth Recordings

In a very small selected group of patients being considered for epilepsy surgery, invasive electrodes may be placed by a Neurosurgeon either on the  surface of the brain or within the brain substance, to record the EEG directly. The electrodes may remain in place for several days and stimulation procedures may be used to map the distribution and spread of seizure activity.