Most epilepsy patients considering surgery undergo the Wada (WAH-dah) test first. This test is officially known as the intracarotid sodium amobarbital procedure (ISAP), but the nickname "Wada test" is commonly used. The name comes from the physician who first performed it, Dr. Juhn Wada.

The Wada test looks at language and memory on one side of the brain at a time. Language (speech) is controlled by one side of the brain (in most people, the left side), and the Wada will tell the doctors which side controls language in your brain. Memory can be controlled by both sides of the brain; the Wada tells which side of your brain has better memory. If the side that controls language or has better memory is where your seizures may be coming from, the surgeon may consider performing an fMRI or brain mapping before surgery.

Who performs the test?

Three doctors are usually involved in performing a Wada test: the neuroradiologist (who uses imaging devices and substances to study the brain), the epileptologist (a neurologist who specializes in epilepsy), and the neuropsychologist (who specializes in the relationship between the brain and how we think and behave).

What's an angiogram?

Right before the Wada test, a cerebral angiogram is done. The angiogram looks at blood flow within the brain to make sure that there are no obstacles to performing the Wada. The neuroradiologist inserts a catheter (a long, narrow tube) into an artery, usually in the leg. The catheter is directed to the right or left internal carotid artery in the neck, which supplies the brain with blood. Once the catheter is in place, a dye is injected. Some patients report a warm sensation when this happens. The dye can be seen on a special x-ray machine. This machine takes pictures of the dye as it flows through the blood vessels of the brain. Once the angiogram is done, the catheter will stay in place for the Wada.

What happens during the Wada test?

During a Wada, the neuroradiologist puts one side of your brain to sleep for a few minutes. This is done by injecting sodium amobarbital (also called sodium amytal) into the right or left internal carotid artery. If the right carotid artery is injected, the right side of the brain goes to sleep and can't communicate with the left side. Once the physicians are sure that one side of your brain is asleep, the neuropsychologist shows you objects and pictures. The awake side of the brain tries to recognize and remember what it sees.

After just a few minutes, the sodium amobarbital wears off. The side that was asleep starts to wake up. Once both sides of your brain are fully awake, the neuropsychologist will ask you what was shown. If you don't remember what you saw, items are shown one at a time, and you are asked whether you saw each one before. Your responses will be recorded word-for-word.

After a delay, the other side of the brain is put to sleep. To do this, the catheter is withdrawn part of the way and threaded into the internal carotid artery on the other side. A new angiogram is done for that side of the brain. Different objects and pictures are shown, and the awake side (which was asleep before) tries to recognize and remember what it sees. Once both sides are awake again, you will be asked what was shown the second time. Then you are shown items one at a time and asked whether you just saw each item.

How long does the test take?

The Wada test can vary between medical centers. In some centers, the delay between the injections is 30 to 60 minutes. Other centers test one side on one day, and test the other side the following day. Between five and twelve items are shown to each side of the brain. You may come in and leave the same day, or you may be asked to come in the day before or stay a day after.

Is the Wada safe?

A Wada test is generally a safe procedure with very few risks. There is a small risk of some complications. These complications can be as minor as pain where the catheter is inserted or as serious as a potential stroke. Since the Wada involves entering arteries, there is a chance that fat inside an artery may come loose and cause a blockage in the brain, leading to a stroke. This risk of stroke is less than 1% overall. It is greater, but still relatively low, if you are older or if you have atherosclerosis (hardening of the arteries) or a history of high cholesterol.

Topic Editor: Howard L. Weiner, M.D.
Last Reviewed:3/8/04