An EEG test monitors and records brain wave activity through electrodes attached to a patient’s scalp. The test is used to diagnose neurological disorders, head injuries, brain diseases, and sleep disorders. The patient may be awake or asleep during the test, and preparation varies depending on the patient’s condition. EEG results may be available several hours after the test.
An EEG, also called an electroencephalography or electroencephalogram, is a test that detects the brain’s electrical activity or brain waves. Doctors often use the test to evaluate head injuries or to diagnose neurological disorders. Depending on the reason for the EEG, the patient may be awake or asleep during the test. Patients may need to spend one to four hours getting tested in a doctor’s office or hospital.
The EEG test monitors and records brain wave activity through the use of electrodes, which consist of small metal discs that attach to a patient’s scalp with a special adhesive. The electrodes connect to wires that are connected to a recording device and an amplifier. The amplifier connects to a computer monitor so a neurologist can interpret the test results. The electrodes help detect any electrical activity generated by the patient’s brain cells.
Patterns of the brain’s electrical activity are often classified into four different types of wave rhythms during the EEG: alpha, beta, delta, and theta. These are used by neurologists to examine how the brain works or reacts while a person is asleep or awake for up to 30 minutes. The patient is tested with activities at each stage, ranging from sedation to responses to light or other stimuli, and sudden bursts of energy.
Each type of wave is recorded at a different speed and indicates something different in relation to the patient’s brain patterns. Alpha waves, registering up to 12 cycles per second, indicate when the patient is awake, but with their eyes closed. Recorded in a pattern of up to 30 cycles per second, beta waves record the brain’s response to sedative drugs. Doctors usually look at delta waves in children or during a patient’s deep sleep, as they are the shortest bursts of activity at 0.5 to 3.5 cycles per second. Theta waves are most often seen in children and young adults and are recorded at up to 7 cycles per second.
Neurologists often administer electrical activity tests to children and adults to diagnose head injuries, brain disease, or sleep disorders. Patients with brain injuries from an accident may have an EEG so doctors can evaluate changes in the brain. The test can also be used to detect a brain tumor or a brain disease such as encephalitis. The electrical activity of the test most commonly detects the presence of epilepsy or other seizure disorders in patients. Alzheimer’s disease or narcolepsy can also be diagnosed with the help of an EEG.
Preparation for the EEG test usually varies depending on the patient’s condition. The evening before the exam, the hair must be washed with shampoo only, as the electrodes would be placed on the scalp. The patient should avoid using conditioners or other hair products as they may interfere with the test results. The doctor may request that the patient stop taking medications or avoid caffeine-containing foods and drinks for several hours. Fasting is prohibited before the test because low blood sugar can skew the results.
Specific sleep schedule instructions may be provided for each patient. For example, a patient may be instructed to reduce sleep the night before if sleep is needed during the EEG. In the doctor’s office or hospital room, the patient may lie flat on a bed or recline in a chair with up to 25 electrodes placed on their head. Proper procedures require the patient to remain still and relaxed, with their eyes closed even though they may be awake. EEG results may be available several hours after the test.
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