What Is the Wada Test?

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  • Written By: Jillian O Keeffe
  • Edited By: Shereen Skola
  • Last Modified Date: 10 August 2019
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Doctors and surgeons employ certain tests to find out more details about specific diseases. The Wada test, which is named after the doctor who pioneered it, is used with patients who are about to undergo brain surgery for epilepsy. Using a combination of anesthetic and behavioral observation, the test helps surgeons to pinpoint the areas of the brain that the patient uses for language and memory. This information helps the doctor to assess if the brain tissue responsible for the epilepsy can be removed without damaging these functions.

Epilepsy involves a malfunction of the brain's electrical signals that may be improved through surgery. Different areas of the brain are responsible for certain functions, ranging from movement to emotions. A surgeon has to balance the chance of improvement in epilepsy against the risk of damage to important brain functions when considering surgery. The areas responsible for using language, and remembering the past, can be present primarily in one side, or hemisphere, of the brain; or, they can be present in both.


When a candidate for epilepsy surgery has the majority of both of these functions on one side of the brain, then the surgeon has a lower risk of creating permanent damage to these functions when operating on the other hemisphere. To check this, he or she performs a Wada test, which involves putting one hemisphere of the brain to sleep at a time. Typically, the doctor injects an anesthetic into one of the two carotid arteries, which both supply different hemispheres of the brain with blood.

With each individual hemisphere asleep, one at a time, the doctor checks how the patient responds to speech and whether he or she is able to talk normally. The capacity of the patient to remember the details of flashcards is also observed. Normally, the patient also wears electrodes on his or her head which ensure the brain is sufficiently asleep for the Wada test to be valid. As the carotid artery is a major blood vessel, the potential for severe blood loss is high, so the patient has to remain lying down for several hours after the Wada test is complete.

A low risk of stroke is associated with this procedure, but less severe effects like headaches and localized pain in the area of the injection are more common. To make the test as accurate and safe as possible, a doctor who specializes in epilepsy and a doctor who is an expert in imaging the brain may be present. Generally, the patient can go home the same day and need only take special care of themselves for two days after the test.


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