An EEG is a painless test where small sensors are placed on your scalp to record your brain’s electrical activity. A routine EEG takes about 20 to 30 minutes, though setup and cleanup add extra time on either side. Here’s what to expect before, during, and after the test.
How to Prepare the Day Before
Preparation starts the night before your appointment. Wash your hair with shampoo only, and skip conditioner, cream, or gel afterward. Hair products leave a residue that prevents the electrodes from making good contact with your scalp, which can result in a poor-quality recording or the need to repeat the test.
You’ll also need to avoid caffeine for at least eight hours before the test. That includes coffee, tea, soda, and chocolate. Caffeine changes your brain’s electrical patterns and can interfere with the results. Your doctor may also give you specific instructions about medications, particularly if the EEG is being done to evaluate seizures.
How Electrodes Are Placed
When you arrive, a technologist will seat you in a reclining chair or have you lie on a bed. They’ll measure your head using bony landmarks (your nose, the bumps behind your ears, and the back of your skull) to map out exactly where each electrode should go. This measurement system, called the 10-20 system, has been the international standard since 1958. It places 21 electrodes at precise, evenly spaced positions across the scalp so that brain activity from every region gets captured.
Before attaching each electrode, the technologist rubs a mildly abrasive cleanser on the spot to remove dead skin cells and oil. This light scrubbing can feel gritty but isn’t painful. Each small, flat electrode is then secured with a conductive paste that helps transmit the electrical signals from your scalp to the recording equipment. The entire setup process typically takes 20 to 30 minutes on its own, separate from the recording time.
What Happens During the Recording
Once the electrodes are in place, the actual recording begins. You’ll be asked to lie still and relax, sometimes with your eyes open, sometimes closed. The technologist will give you clear instructions throughout. For parts of the recording, you simply rest quietly while the machine picks up your brain’s baseline electrical patterns.
Two specific tasks are commonly used to “activate” the brain and bring out abnormal patterns that might not show up at rest:
- Deep breathing: You’ll be asked to breathe deeply and steadily at a fast pace for about 3 to 5 minutes. This temporarily changes the oxygen and carbon dioxide levels in your blood, which can reveal certain types of seizure activity. For children, technologists sometimes use balloons or toy windmills to make the breathing exercise easier to follow.
- Flashing lights: A strobe light is positioned in front of you in a dimly lit room. It flashes at increasing speeds, starting slow (around one flash per second) and building up to about 30 flashes per second, in short bursts of 5 to 10 seconds each. This tests whether flickering light triggers abnormal brain responses. If it does, the technologist stops the light immediately.
Neither of these tasks is painful, though deep breathing can make you feel lightheaded or tingly in your fingers, and the flashing light can feel briefly uncomfortable. Both sensations pass quickly once the task ends.
Is an EEG Safe?
An EEG carries virtually no risk. The electrodes only record electrical activity; they don’t send any electricity into your body. In a large study of over 3,000 patients suspected of having epilepsy, the deep breathing exercise provoked a seizure in about 2% of cases, and only one patient (0.03%) had a full convulsive seizure. Significant heart, lung, or blood vessel complications were not reported. If you do have a seizure during the test, you’re already in a clinical setting with trained staff present.
After the Test
Once recording is complete, the technologist removes the electrodes and cleans off the paste. You’ll likely still have some paste residue in your hair, so plan to wash it again when you get home. There’s no recovery period. You can drive, eat, and go about your day normally. Results are typically read by a neurologist and sent to the doctor who ordered the test, usually within a few days.
Sleep-Deprived EEGs
If a routine EEG comes back normal but your doctor still suspects seizure activity, you may be scheduled for a sleep-deprived EEG. Some abnormal brain patterns only appear when a person is drowsy or falling asleep, and sleep deprivation makes it easier to capture that transition during the test.
The amount of sleep restriction depends on age. Children aged 5 to 12 are typically asked to stay up until midnight and wake at 6 a.m. Teenagers and adults stay up until 2 a.m. and wake at 6 a.m. For toddlers, simply waking them earlier than usual is often enough. The key rule: don’t nap on the way to the appointment, since even a short sleep in the car can cancel out the effects of the sleep deprivation. The test itself is identical to a routine EEG, just with a sleepier patient.
Ambulatory and Long-Term EEGs
Sometimes a 20- to 30-minute window isn’t enough to catch intermittent problems. An ambulatory EEG lets you go home with the electrodes still attached, recording brain activity continuously for one to several days while you go about your normal routine. The electrodes are applied the same way, but the technologist wraps your head in gauze to keep everything secure during daily activities. A small, portable recording device clips to your clothing or sits in a pouch.
Hospital-based long-term monitoring works similarly but takes place in a dedicated unit, often with video recording synchronized to the EEG. This is common when doctors need to see exactly what your body is doing at the same moment an electrical change occurs in the brain. Stays range from a couple of days to a week or more, depending on how frequently events occur.