Electroencephalogram (EEG) before epilepsy surgery

Attaching electroencephalogram (EEG) electrodes onto the head

​​The first step in preparing for epilepsy surgery is for your child to have a routine electroencephalogram (EEG) brain wave recording.

The test takes 60 to 90 minutes. However, if your child needs to take a sedative (see below), please allow up to three hours for your hospital visit. This allows enough time for the EEG and for any medicine to wear off before your child goes home.​

Why does my child need an EEG?

Neurons (nerve cells in the brain) use electrical signals to communicate with each other. An EEG measures this electrical activity to help your child’s doctors see more clearly where seizures start.

Your child may have two EEGs: one while they are awake and another while asleep.​​​ During the test, electrodes are attached to your child’s scalp to record different patterns of activity in the brain while your child does simple tasks or has a short sleep.

The patterns of electrical activity show up as wavy lines on a computer monitor. Doctors are trained to read these wavy lines to identify what might cause a seizure.

Example of an EEG recording

How do I prepare my child for an EEG?

  • Explain what will happen during the EEG in words your child understands.
  • Make sure your child’s hair is freshly washed. Check for any signs of head lice and tell the nurse at the hospital if you see anything.
  • To help the electrodes stay in place during the test, do not use conditioner or styling products in your child's hair after you wash it.

Will my child need to be sedated for an EEG?

An EEG does not hurt, but some children may need a mild sedative (medicine to keep them calm) to help them lie still for the test. The most common sedatives are chloral hydrate or melatonin, a natural substance that helps someone fall asleep.

If your child needs to take a sedative, they must:

  • stop eating solid foods eight hours before the test
  • stop drinking milk, formula or other liquids six hours before the test
  • stop any breastfeeding four hours before the test
  • stop drinking water three hours before the test.

What happens when my child arrives for the EEG?

  1. A technologist will measure your child’s head and mark it with a wax pencil so they know where to place the electrodes.
  2. The technologist will clean the marked areas on your child's head with a gel and use a special paste to attach the electrodes to your child’s scalp. They will then cover the electrodes with gauze.
  3. The technologist will connect the electrodes to the EEG machine.

What happens during an EEG?

The technologist will ask your child to sit or, usually, lie on a bed. They may then ask your child to do different activities, such as:

  • breathe deeply for three minutes
  • open and close their eyes
  • watch flashing bright lights for a few minutes.

While your child does these activities, the EEG machine will continuously record the patterns of electrical activity in their brain as wavy lines on a computer screen. 

May I stay with my child during the EEG?

Yes, you will be able to stay with your child during the test.

Does the test have any risks or side effects?

There are typically no risks or side effects from having an EEG.

What should I expect after an EEG?

Once the test is done, the technologist will remove the electrodes from your child’s scalp. You are then free to go home.

If your child took a sedative, they might be sleepy, grumpy and unsteady and will need to be watched carefully until the medicine wears off (usually about six hours after the test). They can return to their usual activities when they are fully alert again.

Your child’s hair may be a little sticky from the paste that attaches the electrodes to their scalp. You can easily wash the paste away with shampoo and water.

When will I get the test results?

Your doctor will receive the EEG test results and discuss them with you and your child at a follow-up appointment, usually about four to six weeks after the test.

Key points

  • An EEG measures electrical activity in your child's brain to help your child's doctors see more clearly where seizures start.
  • During the test, your child will lie still on a bed and do different activities while electrodes are attached to their scalp to record the activity in the brain.
  • If your child needs to take a sedative before the test, follow any eating and drinking instructions from your child's team.
  • You will be able to discuss the EEG results with your child's doctor about four to six weeks after the test.

​Elysa Widjaja, MD, MPH

Rohit Sharma, RET, REPT


At SickKids

If your doctor has told you that your child needs a sedative for the EEG, a nurse from the neurophysiology department will contact you with instructions on when your child needs to stop eating and drinking before the EEG appointment.

If the EEG is booked without a sedative but you think your child will need it, please contact the neurophysiology department a week before the appointment at 416-813-6297.