Electroencephalograms, or EEGs, are a means of measuring the electrical activity in the brain. The electrodes are placed on the scalp and detect changes in voltage due to electric currents caused by neurons firing near them. EEGs are noninvasive, making them a useful diagnostic tool.
1. EEGs are interpreted based on the frequency of brain waves that occur in a fraction of a second. Delta waves, which range from 0-3 hertz, reflect slow, synchronized bursts of activity occurring in the lower frequency of the brain and are seen during deep sleep or coma. Theta waves, which range from 3-8 hertz, reflect bursts of activity during the dream state. Every person’s brain will generate some of the theta waves, but a patient in a coma may generate strong theta waves because of low arousal levels.
2. An EEG will provide doctors with a visual representation of the brain’s activity, but the images are not concrete enough to be used to make a diagnosis. Instead, a physician will use an EEG to compare the brain waves recorded against the average recorded for a healthy patient. If there is evidence of abnormal activity, such as seizures, confirmed by medical history or other diagnostic tests, then epilepsy is usually diagnosed. An EEG can also show whether drugs or alcohol have affected neuronal activities.
3. An EEG can also be used to determine whether someone is having a seizure. The brain’s electrical activity will continue during a seizure, and special electrodes will record the data. When doctors compare the results with those obtained while a patient is awake and alert, they can usually tell whether the seizure was caused by epilepsy. However, this is not always possible if other conditions are present that may also cause seizures, such as drug or alcohol use, sleep deprivation, or head trauma.
4. EEGs are noninvasive and painless, making them an efficient diagnostic tool in cases of suspected epilepsy. Many hospitals and doctor’s offices are now using portable EEG machines that one can take in the field to conduct the test where other causes for abnormal behavior may be present.
5. EEGs conducted in a hospital or medical office are typically only recorded for a short period, after which they are analyzed and interpreted by a doctor or an EEG reading service. A patient typically wears an electrode cap that resembles a swim cap with electrodes protruding from it. The test can take between 20 minutes and one hour, during which the patient is asked to remain as still as possible to minimize the risk of electrical interference from external sources. Some clinicians may also instruct the patient to perform mental tasks like counting backward numbers beginning with 100.
6. EEGs are most often used after a seizure occurs to identify the area of the brain responsible for epilepsy. Doctors may also use the test as a screening tool to determine whether a patient has Alzheimer’s disease or another disorder that causes similar behavior. Many patients are incorrectly diagnosed with degenerative brain disorders such as Alzheimer’s when they have epilepsy.
EEGs are a helpful method of diagnosing epilepsy. They are also used to determine whether other conditions may be causing seizures, such as traumatic brain injuries caused by accidents or drug and alcohol use. Doctors will typically compare the test results against those obtained when the patient is alert and awake to determine whether any abnormalities are due to epilepsy or another condition. In many cases, doctors use EEGs to monitor patients experiencing seizures to provide them with medication to treat them.