Electroencephalography (EEG)

Electroencephalography, or EEG, records the electrical activity of the brain. Sensitive electrodes are placed on the scalp to pick up electrical charges spreading through the brain. These charges are then mapped on a recording or a computer screen. The mapped electrical activity is interpreted by a neurologist. EEG is also used to look for organic causes of psychiatric symptoms and disabilities in children and can assist physicians in determining irreversible brain death.

During an EEG, highly sensitive monitoring equipment records brain activity through electrodes that are placed at measured intervals on a patient's scalp. The test is not painful. First, the head is measured, and then the electrodes are placed on the scalp with a paste-like substance. The principal role of the patient is to remain still, relaxed, and comfortable.


EEG findings vary depending on the activities during the study. For example, during sleep the brain exhibits a different brain wave pattern as compared to wakefulness. The brain also generates different wave patterns depending on the type of epileptic seizure. The most informative pattern of change on routine EEGs, which occurs in between seizures, is called an epileptiform discharge. This is an abnormal buildup of electrical activity that typically occurs in the area of the brain causing the seizures.

Importantly, brain waves vary unpredictably in between seizures, and only 35-50 percent of people with epileptic seizures will show a definitive epileptiform discharge on routine EEG studies. Understanding these epileptiform patterns, along with a complete neurological exam and medical history, enables Dr Raj to determine the type of epilepsy and make recommendations for the best course of treatment.

What happens during the procedure?

For the procedure, patients lie on their back with their eyes closed, while approximately 17 to 21 metal sensor plates or electrodes are attached to the head, with a sticky paste. Alternatively, patients may have a cap containing electrodes fixed to their heads, which can be attached using tiny needles. The electrodes are attached by wires to a computer that records the electrical activity of a patient’s brain through a series of wavy lines. Patients are asked to remain relaxed during the procedure.

Also, patients may be asked to perform different tasks, while being tested to examine their brain’s reaction, including hyperventilating, looking at a strobe light or being asked to sleep or given a sedative.

The test usually lasts 1 to 2 hours, and normal activity can resume afterwards.

No pain is involved during the EEG test; however, if needle electrodes are used, patients will feel a slight prick on their scalp.

The actual test is safe, as no electric currents are run through a patient’s body.