Wada test

  The Wada test, also known as the "intracarotid sodium amobarbital procedure" (ISAP), is used to establish which cerebral functions are localized to which hemisphere.

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Method

The test is conducted with the patient awake. Essentially, a barbiturate (which is usually sodium amobarbital) is introduced into one of the internal carotid arteries via a cannula or intra-arterial catheter from the femoral artery. The drug is injected into one hemisphere at a time. The effect is to shut down any language and/or memory function in that hemisphere in order to evaluate the other hemisphere ("half of the brain"). Then the patient is engaged in a series of language and memory related tests. The memory is evaluated by showing a series of items or pictures to the patient so that within a few minutes as soon as the effect of the medication is dissipated, the ability to recall can be tested.

There is currently great variability in the processes used to administer the test, and so it is difficult to compare results from one patient to the other.^[1]

Uses

The test is usually performed prior to ablative surgery for epilepsy and sometimes prior to tumor resection. The aim is to determine which side of the brain is responsible for certain vital cognitive functions, namely speech and memory. The risk of damaging such structures during surgery can then be assessed, and the need for awake craniotomies can be determined as well.

The Wada test has several interesting side-effects. Drastic personality changes are rarely noted, but disinhibition is common. Also, contralateral hemiplegia, hemineglect and shivering are often seen. During one injection, typically the left hemisphere, the patient will have impaired speech or be completely unable to express or understand language. Although the patient may not be able to talk, sometimes their ability to sing is preserved. This is because music and singing utilizes a different part of your brain than speech and language. Most people with aphasia are able to sing, and even learn new songs (as in the case of Cesero Rota, klawans, 2002).Recovery from the anesthesia is rapid, and EEG recordings and distal grip strength are used to determine when the medication has worn off. Generally, recovery of speech is dysphasic (contains errors in speech or comprehension) after a dominant hemisphere injection. Although generally considered a safe procedure, there are at least minimal risks associated with the angiography procedure used to guide the catheter to the internal carotid artery. As such, efforts to utilize non-invasive means to determine language and memory laterality (e.g. fMRI) are being researched.

History

The Wada test is named after a Canadian neuropsychologist known as Juhn A. Wada.^[2][3] He developed the test after noticing certain people with left brain damage still preserved their ability to speak and understand language. The test was thought up by a meeting involving Wilder Penfield, Brenda Milner, and Juhn Wada, in which Penfield was discouraged about not being positive about the lateralization of language. Wada spoke up, mentioned the injection of sodium amytal putting one hemisphere to sleep, and it was then used to test for lateralization.

References

See also

• Dual brain theory