Wada test
Encyclopedia
The Wada test, named after Canadian neurologist and epileptologist Juhn Atsushi Wada
, also known as the "intracarotid
sodium
amobarbital
procedure" (ISAP), is used to establish cerebral
language and memory representation of each hemisphere
.
(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.
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 post-operative cognitive change can be estimated, and depending on the surgical approach employed at the epilepsy surgery center, 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 and language 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 the brain than speech and language. Recovery from the anesthesia is rapid, and EEG recordings and distal grip strength may be used to determine when the medication has worn off. Generally, recovery of speech is dysphasic (contains errors in speech or comprehension) after a language 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 which may be related to experience. As such, efforts to utilize non-invasive means to determine language and memory laterality (e.g. fMRI, magnetoencephalography
and near-infrared spectroscopy) are being researched.
, of the University of British Columbia. He developed the test while he was a medical resident in Japan just after World War II, when he was receiving training in neurosurgery. Wada developed the technique of transient hemispheric anesthetization through carotid amytal injection to decrease the cognitive side effects associated with bilateral electroconvulsive therapy . He published the initial description of motor, sensory, language, and effects on the "conscious state" in 1949, in Japanese. During his fellowship at the Montreal Neurological Institute, he introduced the test to the English-speaking world.
Juhn Atsushi Wada
Juhn Atsushi Wada, OC is a Japanese Canadian neurologist known for research into epilepsy, including his description of the Wada test for cerebral hemispheric dominance of language function.- Biography :...
, also known as the "intracarotid
Carotid artery
Carotid artery can refer to:* Common carotid artery* External carotid artery* Internal carotid artery...
sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
amobarbital
Amobarbital
Amobarbital is a drug that is a barbiturate derivative. It has sedative-hypnotic and analgesic properties. It is a white crystalline powder with no odor and a slightly bitter taste. It was first synthesized in Germany in 1923...
procedure" (ISAP), is used to establish cerebral
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
language and memory representation of each hemisphere
Cerebral hemisphere
A cerebral hemisphere is one of the two regions of the eutherian brain that are delineated by the median plane, . The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres has an outer layer of grey matter called the cerebral cortex that is...
.
Method
The test is conducted with the patient awake. Essentially, a barbiturateBarbiturate
Barbiturates are drugs that act as central nervous system depressants, and can therefore produce a wide spectrum of effects, from mild sedation to total anesthesia. They are also effective as anxiolytics, as hypnotics, and as anticonvulsants...
(which is usually sodium amobarbital) is introduced into one of the internal carotid arteries via a cannula
Cannula
A cannula or canula is a tube that can be inserted into the body, often for the delivery or removal of fluid or for the gathering of data...
or intra-arterial catheter
Catheter
In medicine, a catheter is a tube that can be inserted into a body cavity, duct, or vessel. Catheters thereby allow drainage, administration of fluids or gases, or access by surgical instruments. The process of inserting a catheter is catheterization...
from the femoral artery
Femoral artery
The femoral artery is a general term comprising a few large arteries in the thigh. They begin at the inguinal ligament and end just above the knee at adductor canal or Hunter's canal traversing the extent of the femur bone....
. 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.
Uses
The test is usually performed prior to ablative surgeryAblative brain surgery
Ablative brain surgery is the surgical ablation by burning or freezing of brain tissue to treat neurological or psychological disorders. The lesions it causes are irreversible....
for epilepsy
Epilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...
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
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
. The risk of post-operative cognitive change can be estimated, and depending on the surgical approach employed at the epilepsy surgery center, the need for awake craniotomies
Craniotomy
A craniotomy is a surgical operation in which a bone flap is temporarily removed from the skull to access the brain. Craniotomies are often a critical operation performed on patients recording, brain imaging, and for neurological manipulations such as electrical stimulation and chemical...
can be determined as well.
The Wada test has several interesting side-effects. Drastic personality changes are rarely noted, but disinhibition
Disinhibition
Disinhibition is a term in psychology used to describe a lack of restraint manifested in several ways, including disregard for social conventions, impulsivity, and poor risk assessment. Disinhibition affects motor, instinctual, emotional, cognitive and perceptual aspects with signs and symptoms...
is common. Also, contralateral hemiplegia
Hemiplegia
Hemiplegia /he.mə.pliː.dʒiə/ is total paralysis of the arm, leg, and trunk on the same side of the body. Hemiplegia is more severe than hemiparesis, wherein one half of the body has less marked weakness....
, hemineglect and shivering are often seen. During one injection, typically the left hemisphere, the patient will have impaired speech and language 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 the brain than speech and language. Recovery from the anesthesia is rapid, and EEG recordings and distal grip strength may be used to determine when the medication has worn off. Generally, recovery of speech is dysphasic (contains errors in speech or comprehension) after a language 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 which may be related to experience. As such, efforts to utilize non-invasive means to determine language and memory laterality (e.g. fMRI, magnetoencephalography
Magnetoencephalography
Magnetoencephalography is a technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using arrays of SQUIDs...
and near-infrared spectroscopy) are being researched.
History
The Wada test is named after Canadian neurologist Juhn Atsushi WadaJuhn Atsushi Wada
Juhn Atsushi Wada, OC is a Japanese Canadian neurologist known for research into epilepsy, including his description of the Wada test for cerebral hemispheric dominance of language function.- Biography :...
, of the University of British Columbia. He developed the test while he was a medical resident in Japan just after World War II, when he was receiving training in neurosurgery. Wada developed the technique of transient hemispheric anesthetization through carotid amytal injection to decrease the cognitive side effects associated with bilateral electroconvulsive therapy . He published the initial description of motor, sensory, language, and effects on the "conscious state" in 1949, in Japanese. During his fellowship at the Montreal Neurological Institute, he introduced the test to the English-speaking world.
External links
- Image at University of Hong Kong
