Electroencephalogram (EEG)

What is a Electroencephalogram (EEG)?

An electroencephalogram (also called EEG) is a diagnostic tool used to record, measure and monitor the brain’s electrical activity with the use of special sensors (or electrodes) that are superficially attached from the scalp. These electrodes are attached to a specialized computer so that the behavior of electric waves can be studied by the physician in order to arrive with a specific diagnosis.

The human brain is composed of a complex network of nerves which uses electrical impulses that are passed from one nerve to another in order to send thoughts, emotions, and commands. The constant traffic of incoming and outgoing electrical signals may come from within various parts of the body and external environment. The patterns of electrical waves that occur in the brain in response to touch, sound, light and stress (such as lack of sleep) are recorded by a EEG in order to aid in identifying underlying cause of a disease or condition. A deviation from the normal trend of electrical impulses within the brain may be a sign of a medical abnormality. In this case, an EEG may be ordered by a physician.

Why are EEGs performed?

EEGs are performed to rule out, provide information or confirm the diagnosis of a condition or disease. Some of which are, but not limited to, the following:

  • Sleep disorders like
    • Narcolepsy
  • Brain infections or the collection of fluid in the brain
    • e.g. Meningitis
  • Brain hemorrhage
  • Degenerative brain disorders like
    • Alzheimer’s
    • Dementia
  • Metabolic conditions that affect brain tissue
  • Hormonal conditions that affect brain tissue
  • Stroke or cerebrovascular accident (death of brain tissues because of blockage in blood flow)
  • Malignancies and tumors of the brain
  • Establish the brain function of coma patients
  • Head injuries and trauma

The results of EEG are typically deciding factors in the course of treatments prescribed.

How does an Electroencephalogram work?

Small electrodes (wires) attached to the scalp with paste are used to amplify electrical signals from the brain. These electrodes are connected to a polygraph machine or computer to record and graphically present brain signals in a wave-like pattern. For example, a spike seen on the EEG graph may indicate abnormal burst of electricity indicative of a typical epileptic activity.

There are several types of EEGs. Depending on the disease condition that is being ruled out, your physician will determine which among the following types of EEGs will be used in order to get a useful reading of your brain’s electrical signals.

  • Sleep EEG: Sleep EEGs are done while the patient is asleep or when tired. This is usually done within the hospital premises.
  • Sleep Deprived EEG: This type of EEG is done while the patient is asleep, only that the patient is intentionally kept awake and deprived of sleep. This is to assess the effect of sleep deprivation in the brain waves.
  • Ambulatory EEG: Ambulatory EEG is carried out if a normal EEG gives an ambiguous result. The patient is given a portable EEG device which records the brain waves while the patient performs normal daily activities.
  • Video-Telemetry: Video telemetry is ambulatory EEG combined with a camera that records the patient’s brain waves correlated with video image of the patient’s activities. Video-telemetry is prescribed if the diagnosis for seizure is unclear.

When is an Electroencephalogram ordered?

EEG is ordered to rule out and identify the presence of a neurologic disorder, such as seizures and sleep disorder. EEG are also useful to assess the extent of damage caused by nerve lesions (such as nerve damage found in brain stroke, physical trauma), and other psychiatric conditions like dementia and Alzheimer’s disease. In children, a EEG may be useful in diagnosing obstructive sleep apnea (complete or partial blockage of upper airway passage while sleeping, characteristically manifested by snoring).

How is Electroencephalogram done?

Around 20 electrodes with wires are placed on a patient’s scalp. Before the test, the patient should ensure that their hair is clean and free from any wax, gel or styling products. No hair accessories can be worn. Patients may eat before the test but should refrain from drinking caffeinated beverages at least 4 hours before the procedure. During the procedure, the technician may ask you to do certain task such as standing, sitting and may even display flashing light to your eyes. Most of the time, you will be lying on a reclining chair with eyes closed.

What to expect after the procedure?

The paste applied on your scalp will cleaned off and the electrodes will be removed quickly. EEGs are generally painless and safe, and the patient may go home right after the procedure. The results will be evaluated by a physician to study the trend of brainwaves in order to correlate results to diagnosis.