Wada test
From Psy3242
Contents |
Overview
The Wada Test, officially referred to as the intracarotid sodium amobarbital procedure or ISAP, is named after Dr. Juhn E. Wada, the first physician who performed it. It is used to determine localization, that is which functions are located in which part of the brain. The test consists of administering a drug, sodium amytal, to the internal carotid artery one hemisphere at a time, thereby inducing a temporary lesion lasting only a few minutes. Before injecting the drug, the patient is given tests measuring his or her abilities in speech, object naming, and memory. While one hemisphere is anesthetized, the neuropsychologist then tests the other hemisphere to evaluate how well it manages speech, naming, and memory.
Tests
The tests used for the Wada procedure vary depending on the center. The Montreal Neurological Instituted technique, however, can be used as a guide on the types of tests given and how the results are used. Memory tests usually consist in showing the patient five items that test both his or her verbal and visual memory. For example, the patient may be asked to memorize two pictures of an object, an actual object, a word, and then a sentence. After the anesthetic wears off, the patient will be asked to recall or choose among a number of items, the original five items shown when only one hemisphere was awake. If the majority of items cannot be remembered, the temporal lobe and hippocampus that stayed awake cannot mediate memory. This information is important because if temporal lobe needs to be removed, for a person with epilepsy for example, the removal would not cause a problem since this lobe is already known to be dysfunctional. Likewise if the other hemisphere was the one with the epileptic focus, removing that temporal lobe and the hippocampus may cause amnesia in the individual.
Modern Uses of the Wada Test
Functional magnetic resonance imaging (fMRI) has increasingly been taking the place of the Wada test, which can be more invasive and less accurate. The fMRI, on the other hand, has been used to directly visualize the origin of seizures and to detect blood flow changes. Although radical personality changes are rarely noticed in patients who undergo the Wada procedure, disinhibition, hemiplegia, hemineglect, and shivering are common. The Wada procedure, though, does not usually cause long term problems and for a person who suffers from constant seizures, completing the Wada procedure successfully can be life-changing.
Difference in Brain Organization between Right and Left-Handers?
The Wada Test put to rest the belief that the left hander's brain was the mirror image of the right hander's brain. Results from the test showed the pattern of lateralization found in most right-handers was the same in about 70% of left-handers. Of the 30% remaining, half showed the opposite pattern (known as reversed asymmetry) and the other half showed language and spatial skills distributed in both hemispheres (referred to as bi-lateral distribution).
Resources
- http://www.epilepsy.com/epilepsy/surgery_wada
- http://www-personal.umich.edu/~gusb/wadadesc.html
- Stirling, John. Introducing Neuropsychology
- Ogden, Jenni A. Fractured Minds: A Case Study Approach to Clincial Neuropsychology.
