An electroencephalogram (EEG) detects electrical activity in the brain. Electrodes are attached to the scalp and electrical activity shows up as wavy lines on the screen of an electroencephalogram monitor or printed out on paper from the monitor. A neurologist then interprets the reading to determine if it is normal or not. If not, the doctor may also be able to determine the type of abnormality and in which part of the brain the abnormality is occurring. The test is done under a number of conditions, such as when you are awake, when you are sleeping, during a seizure, when you are being stimulated with light, etc.
An EEG can determine changes in brain activity that might be useful in diagnosing brain disorders, especially epilepsy or another seizure disorder. An EEG might also be helpful for diagnosing or treating the following disorders: -Brain tumor -Brain damage from head injury -Brain dysfunction that can have a variety of causes (encephalopathy) -Inflammation of the brain (encephalitis) -Stroke -Sleep disorders An EEG might also be used to confirm brain death in someone in a persistent coma. A continuous EEG is used to help find the right level of anesthesia for someone in a medically induced coma.
-EEG allows your doctor to see brain activity as it unfolds in real time, at the level of milliseconds.
-During an EEG, it may be difficult to figure out where in the brain the electrical activity is coming from.
You will feel little or no discomfort during an EEG. The electrodes don't transmit any sensations. They just record your brain waves. A technician measures your head and marks your scalp with a special pencil to indicate where to attach the electrodes. A technician attaches discs (electrodes) to your scalp using a special adhesive. Sometimes, an elastic cap fitted with electrodes is used instead. The electrodes are connected with wires to an instrument that amplifies the brain waves and records them on computer equipment. Once the electrodes are in place, an EEG typically takes up to 60 minutes. Testing for certain conditions require you to sleep during the test. In that case, the test can be longer. You relax in a comfortable position with your eyes closed during the test. At various times, the technician might ask you to open and close your eyes, perform a few simple calculations, read a paragraph, look at a picture, breathe deeply for a few minutes, or look at a flashing light. Video is routinely recorded during the EEG. Your body motions are captured by a video camera while the EEG records your brain waves. This combined recording can help your doctor diagnose and treat your condition.
There are some things you should do to prepare for EEG: Don’t eat or drink anything with caffeine for 8 hours before the test. Your doctor may give you instructions on how much to sleep if you’re expected to sleep during the EEG. Eat normally the night before and day of the procedure. Low blood sugar could mean abnormal results. Let your doctor know about any medications -- both prescription and over-the-counter -- and supplements you're taking. Wash your hair the night before the test. Don't use any leave-in conditioning or styling products afterward. If you are wearing extensions that use glue, they should be removed.
Once the test is complete, the technician removes the electrodes and washes off the sticky paste with warm water. Hair washing may be needed in order to remove remnants of the paste. You may return to his or her normal routine immediately after an EEG. A specialist doctor will read and interpret the EEG and discuss your results.
EEGs are safe. If you have a medical condition, talk with the doctor about it before your test. If you have a seizure disorder, there’s a slight risk that the flashing lights and deep breathing of the EEG could bring on a seizure. This is rare. A medical team will be on hand to treat you immediately if this happens. In other cases, a doctor may trigger a seizure during the test to get a reading. Medical staff will be on hand so the situation is closely monitored.
How Does an EEG Work?
The billions of cells in your brain produce very small electrical signals that form non-linear patterns called brainwaves. An EEG machine measures the electrical activity in the cerebral cortex, the outer layer of the brain, during an EEG test. EEG sensors are placed on a participant’s head, then the electrodes non-invasively detect brainwaves from the subject. EEG sensors can record up to several thousands of snapshots of the electrical activity generated in the brain within a single second. The recorded brainwaves are sent to amplifiers, then to a computer or the cloud to process the data. The amplified signals, which resemble wavy lines, can be recorded on a computer, mobile device, or on a cloud database. Cloud-computing software is considered a critical innovation in EEG data processing, as it allows for real-time analysis of recordings at scale—in the early days of EEG measurement, waves were simply recorded on a graph paper. EEG systems in academic and commercial research typically show the data as a time series, or as a continuous flow of voltages.
Is an EEG Painful?
An EEG is not painful. Small button-like electrodes are placed in precise spots on the head. For most patients a combination of special paste and glue is used to ensure the electrodes stay in place. At the end of the EEG study a solution is used to remove the glue, and electrodes and paste are washed away with damp wash cloths.