Determination of language dominance using functional MRI

Abstract

Article abstract-We performed functional MRI (FMRI) in 22 consecutive epilepsy patients undergoing intracarotid amobarbital (Wada) testing and compared language lateralization measures obtained with the two procedures. FMRI used a single-word semantic decision task previously shown to activate lateralized language areas in normal adults. Correlation between the two tests was highly significant (r = 0.96; 95% CIS 0.90 to 0.98; p < 0.0001). These results validate the FMRI technique and suggest that "active" areas observed with this semantic processing task correspond to those underlying hemispheric dominance for language. The strong correlation observed supports the view that language lateralization is a continuous rather than a dichotomous variable. In addition to lateralization information, FMRI consistently demonstrated focal regions of activity in lateral frontal and temporo-parieto-occipital cortex. These functional maps may be helpful in defining the boundaries of surgical excisions. NEUROLOGY 1996;46:978-984 Localization of cortical functions in patients undergoing excisional brain surgery is useful in three ways: to predict the general level of risk should the planned excision proceed, to guide the surgeon in limiting the boundaries of the excision, and to help determine the location of abnormal brain areas (e.g., seizure foci) preoperatively. One commonly used localization technique is the intracarotid amobarbital, or Wada, test, which measures the relative lateralization of language and memory functions across the two hemispheres. Preoperative determination of language lateralization is important in selecting patients for more invasive and specific localization procedures, such as intraoperative stimulation mapping." Determination of language lateralization is particularly important in the preoperative evaluation of epilepsy patients, because this population may have a higher incidence of atypical language dominance than does the normal p o p~l a t i o n .~?~ Although there are several alternative methods for determining language d~m i n a n c e ,~,~ the Wada test remains the only method used routinely for this purpose.The Wada test, although a proven measure of language lateralization, has several important limitations. First, the required angiographic procedure is invasive, with reported complication rates of up to 3%1.8 Second, the test measures only the relative distribution of language across the two hemispheres. More specific information about localization within a hemisphere, which might be useful for tailoring an excision, must be obtained by other means, such as intraoperative stimulation mapping. Third, validity of the test depends on demonstration of relatively separate and symmetric arterial supply routes for the two hemispheres. Thus, interpretation of the test may not be straightforward or possible in patients with azygous supply patterns or arterial crossflow.!' Other methodologic drawbacks of the Wada test are limitations on the time available for testing distinct functions during the ...

Role of the Wada test and functional magnetic resonance imaging in preoperative mapping of language and memory: two atypical cases

“…The resulting activation map includes only primary language areas with significance of activation at p < .000125. Laterality indices were then calculated (L − R/L + R), such that −1 = right while +1 = left (Binder et al, 1996).…”

Hemodynamic Assessment of Carotid Stenosis by Functional Magnetic Resonance Imaging

“…The size of clusters in the hand area was quantified in pixels (pc left/right ). The asymmetry index (AI) was then calculated by the following formula according to other imaging protocols [5, 14, 15]:…”

Clinical Functional Magnetic Resonance Imaging (fMRI)

“…With a measuring time of 234 s robust functional localization of Broca's and Wernicke's areas can be achieved, as well as of the anatomically homologous areas in the right hemisphere, as a basis for calculating regional lateralization indices ( Figure 5). The BOLD signals correlate well in all the areas mentioned with the hrf (r > 0.65) and signal intensities typically range between 1% and 2% at 1.5 T [21]. Both paradigms (sentence generation and word generation, each nonvocalized and vocalized) are triggered visually and can be adjusted to the ability of individual patients by varying the trigger frequency.…”

“…To investigate motor function, self-triggered movements are most commonly used [19], and nonstandardized tactile stimuli (e.g., manual stroking of the hand by the examiner) to measure somatosensory function [20]. Language functions are examined using various paradigms involving acoustic [21] or visual [22] stimulation. In different clinical fMRI trials the measurement times required per paradigm show a high variability between 1 min [23] and > 20 min [24]; technical and methodological differences are also significant.…”

“…The use of optically adjustable reflective lenses in patients with visual impairment permits correction [32]. At the same time, the visual stimulation prevents possible unwanted superposition of speech-associated activation in the Wernicke speech center (BA21) by activation of the closely neighboring auditory cortex (BA41, 42), as can occur in the case of acoustic stimulation [21]. Contrary to the movement tasks for the motor fMRI, which are simple to perform, examining cognitive brain functions, i.e., that of speech, requires very close cooperation of the patient.…”