What is Electroencephalography?


via The Medical City |

Electroencephalography (EEG) is a procedure which involves placing electrodes on the scalp in predetermined locations to record the surface electrical activity of the brain and thereby determine brain function.

How is it done?

Technicians perform the procedure. Electrodes are placed on the patient’s scalp at specific locations using special adhesive agents. The patient is asked to lie quietly on the bed and may be given simple instructions such as open/close eyes or breathe deeply.  At one point during the recording, flashing lights will be placed in front of the eyes. They look for abnormal electrical activities in the brain. They also isolate and mark artifacts (a structure not normally present but produced by some external action; something artificial) so that the encephalographer is guided when interpreting the tracing.

Anyone can undergo the procedure. Some patients may, at times, require preparation, for example sleep deprivation.

Preparations needed for the procedure are individualized, which is why an EEG, unless absolutely immediately needed, must be scheduled, so that technicians may give pre-EEG instructions to the patients. Some medications may be withheld before an EEG. Some patients may need to be deprived of sleep.

What are the indications for Electroencephalography?

The neurologist or physician must evaluate the patient before he is subjected to the test. Individual symptoms or signs cannot be used as the sole basis to have an EEG done. It is the collective presentation of the patient that guides each physician to request for an EEG. 

How long does the procedure take?

The procedure takes around 45-60 minutes. After the procedure, the electrodes and adhesive agent are removed and the patient is given the option to rinse their hair. Hair dryers and towels are provided after each EEG.

What is experienced by the patient during the procedure?

The EEG itself does not put stress on the patient and has almost no complications. After the procedure the patient will feel normal. They may go through their daily routine, but in some instances, such as if their maintenance medication was withheld, control of their illness may be compromised and a patient may require rest for a few days, just until normal drug levels in the blood are again maintained.

When will the result of the examination be known? 

Results will be available after two working days for outpatients and one day for inpatients except Sundays and Holidays

What are the benefits of the procedure?

The EEG is the main test used to record brain activities and demonstrate brain function. It is frequently requested for suspected seizures or epilepsy. Other tests which may test the integrity of specific symptoms of the brain include the VEP (Visual Evoked Potential), SSEP (Somatosensory Evoked Potential), and BAEP (Brainstem Auditory Evoked Potential).  Tests which show brain structure, rather than brain function, are CT scan and Magnetic Resonance Imaging (MRI).  These tests are all available at The Medical City and are used in conjunction with each other depending on the individual need of the patient as each test provides different information about the brain.

What are the risks of the procedure?

Reactions or allergies to the EEG paste/gel used.

Meticulous mechanical preparations by skilled technicians are done before each procedure. One of the risks involved in EEG is accidental electrocution; however, all our machines are double grounded, undergo regular maintenance checks and are checked before each patient.

How can The Medical City help you?

At The Medical City, we have a complete roster of board certified and competent Neurophysiologists who can give you medical advice, diagnosis and treatment.

For inquiries, you may contact:


2/F Podium Building, The Medical City
Tel. No.: (632) 988-1000 / (632) 988-7000 Ext. 6269


TMC Department of Neurology
Fisch & Spehlmann’s Third Revised and Enlarged Edition EEG Primer
(Basic Principles of Digital and Analog EEG) by Bruce J. Fisch