Language dominance and factors that influence language lateralization were investigated in right-handed, neurologically normal subjects (n = 100) and right-handed epilepsy patients (n = 50) using functional MRI. Increases in blood oxygenation-dependent signal during a semantic language activation task relative to a non-linguistic, auditory discrimination task provided an index of language system lateralization. As expected, the majority of both groups showed left hemisphere dominance, although a continuum of activation asymmetry was evident, with nearly all subjects showing some degree of right hemisphere activation. Using a categorical dominance classification, 94% of the normal subjects were considered left hemisphere dominant and 6% had bilateral, roughly symmetric language representation. None of the normal subjects had rightward dominance. There was greater variability of language dominance in the epilepsy group, with 78% showing left hemisphere dominance, 16% showing a symmetric pattern and 6% showing right hemisphere dominance. Atypical language dominance in the epilepsy group was associated with an earlier age of brain injury and with weaker right hand dominance. Language lateralization in the normal group was weakly related to age, but was not significantly related to sex, education, task performance or familial left-handedness.

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 ...

Preoperative fMRI predicted naming decline in patients undergoing left anterior temporal lobectomy surgery.

SUMMARYPurpose: Verbal memory decline is a frequent complication of left anterior temporal lobectomy (L-ATL). The goal of this study was to determine whether preoperative language mapping using functional magnetic resonance imaging (fMRI) is useful for predicting which patients are likely to experience verbal memory decline after L-ATL. Methods: Sixty L-ATL patients underwent preoperative language mapping with fMRI, preoperative intracarotid amobarbital (Wada) testing for language and memory lateralization, and pre-and postoperative neuropsychological testing. Demographic, historical, neuropsychological, and imaging variables were examined for their ability to predict pre-to postoperative memory change. Results: Verbal memory decline occurred in over 30% of patients. Good preoperative performance, late age at onset of epilepsy, left dominance on fMRI, and left dominance on the Wada test were each predictive of memory decline. Preoperative performance and age at onset together accounted for roughly 50% of the variance in memory outcome (p < 0.001), and fMRI explained an additional 10% of this variance (p ≤ 0.003). Neither Wada memory asymmetry nor Wada language asymmetry added additional predictive power beyond these noninvasive measures. Discussion: Preoperative fMRI is useful for identifying patients at high risk for verbal memory decline prior to L-ATL surgery. Lateralization of language is correlated with lateralization of verbal memory, whereas Wada memory testing is either insufficiently reliable or insufficiently material-specific to accurately localize verbal memory processes.

SUMMARYAims: Many fMRI protocols for localizing speech comprehension have been described, but there has been little quantitative comparison of these methods. We compared five such protocols in terms of areas activated, extent of activation, and lateralization. Methods: fMRI BOLD signals were measured in 26 healthy adults during passive listening and active tasks using words and tones. Contrasts were designed to identify speech perception and semantic processing systems. Activation extent and lateralization were quantified by counting activated voxels in each hemisphere for each participant. Results: Passive listening to words produced bilateral superior temporal activation. After controlling for prelinguistic auditory processing, only a small area in the left superior temporal sulcus responded selectively to speech. Active tasks engaged an extensive, bilateral attention, and executive processing network. Optimal results (consistent activation and strongly lateralized pattern) were obtained by contrasting an active semantic decision task with a tone decision task. There was striking similarity between the network of brain regions activated by the semantic task and the network of brain regions that showed taskinduced deactivation, suggesting that semantic processing occurs during the resting state. Conclusions: fMRI protocols for mapping speech comprehension systems differ dramatically in pattern, extent, and lateralization of activation. Brain regions involved in semantic processing were identified only when an active, nonlinguistic task was used as a baseline, supporting the notion that semantic processing occurs whenever attentional resources are not controlled. Identification of these lexical-semantic regions is particularly important for predicting language outcome in patients undergoing temporal lobe surgery.