Diagnosis -Wada Testing
Wada testing is named after its developer, Jun Wada. The goal of Wada testing is to determine which side of the brain processes language (i.e., which side is responsible for understanding spoken and written language and for writing and speaking) and to determine whether memory functions normally in each hemisphere (i.e., the left and right halves of the brain). Memory testing is particularly important if epilepsy surgery with partial temporal lobe removal is being planned. As it turns out, the hippocampus within the temporal lobe that is often the source of seizures may also be important for making memories. As long as one hippocampus (either the left or right) has good function then normal memory making can occur. The Wada test is therefore done to make sure that if one hippocampus is removed the other will function normally.
The Wada test is performed during a cerebral angiogram. During the angiogram a short acting sedative is injected through a catheter (tube) that runs inside the body from the groin area through the arterial system up to the neck. Once the sedative (usually amobarbital) is injected into the carotid artery of the neck, it is carried by the blood stream to the brain. Because each carotid artery (left or right) supplies only one side of the brain, the medication only affects one half of the brain. The patient remains awake during the injection and is then asked to remember a series of words and objects. The medication wears off after about 4 minutes. 10 minutes after the injection the patient is asked to recall the words and objects. In a normal person memory function would continue on the side of the brain that is not injected during testing. If the patient can remember test items, then it shows that the opposite side of the brain that remained awake during testing is capable of forming new memories. That information allows the surgical team to proceed with the safe resection of the temporal lobe on the side that was injected, knowing that the other temporal lobe and hippocampus will be able to maintain memory function after surgery.