It is sometimes necessary to know which side of the brain (hemisphere) controls speech. Often, this information is needed when surgery for epilepsy is planned. A test called the WADA test can be performed. The electrodes and wires for an electroencephalogram (EEG, a test that looks at brain waves) are placed on the scalp. The neurologist performs a baseline examination and asks the patient to remember three objects. A catheter is then placed into an artery (usually in the leg, like for an angiogram of the heart) and threaded up to the arteries supplying the brain and an angiogram is performed. The catheter is then left in the carotid artery on the side of interest.
A drug is injected through the catheter causing that side of the brain to stop working briefly. This is done while the EEG is monitored and the neurologist examines the patient. The neurologist then performs several tests of the patient's memory, ability to understand, and ability to speak. The drug wears off quickly (before the end of the test). The patient can go home later the same day.
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