![]() Functional magnetic resonance imaging (fMRI) for language mapping has the potential to provide a noninvasive alternative, which may yield more information on spatial localization. Many epileptic patients often also undergo electrocortical stimulation mapping (ESM), which is another invasive means of obtaining information on functional localization. Furthermore, although the Wada procedure provides significant information about hemispheric dominance, it provides no information on the localization of the brain regions activated in response to a specific cognitive task, which prior to surgery could be of great significance. Although currently a gold standard for both memory and language assessments of laterality, the risks and the variable patient response to the procedure has to some extent limited the interpretation of the results ( Loring et al., 1990 Snyder et al., 1990 Hart et al., 1991 Jeffery et al., 1991 Meador & Loring, 1999). This procedure is invasive, entails some risk, and often the patient is not comfortable during the period of the test and so it is usually not repeated. ![]() The Wada test findings represent a categorical classification of the left, right or bilateral hemisphere(s) being dominant for a particular cognitive function. This test determines the lateralization of the cerebral hemispheres by suppressing cortical activity in one of the hemispheres while testing the patient’s ability to perform certain language or memory-related tasks with the other hemisphere, and then repeating the same procedure suppressing activity in the opposite hemisphere. The Wada procedure (also known as the Intracarotid Amytal Test) ( Wada & Rasmussen, 1960) is a standard clinical test to determine hemispheric dominance typical for both language and memory processing. ![]() This is essential, as it is vital to spare these activated brain regions in order to preserve function following surgery. Identifying the network of the different brain regions involved in a particular cognitive task assists the neurosurgeon in surgical decision-making. In presurgical planning it is crucial not only to identify the role of specific brain areas but also to determine hemispheric dominance for language to avoid postoperative deficits. In patients with neurologic disorders such as epilepsy, it is essential to have an understanding of how organization may be changed in patient populations. If surgical intervention is planned, both dominant and nondominant activity associated with language processing should be evaluated. However, in a small percentage of the population, the right hemisphere is dominant for language, and sometimes there is bilateral dominance ( Pujol et al., 1999 Springer et al., 1999). In the majority of the adult healthy human population, the left hemisphere is dominant for language function. Overall fMRI was in agreement with the Wada test in 91.3% of patients, suggesting its utility for clinical use with the proper consideration given to the confounds discussed in this work. The patients categorized as bilateral via the Wada procedure showed some hemispheric dominance in fMRI, and discrepancies between the Wada test findings and the functional laterality scores arose for a range of reasons.ĭiscussion: Discordance was dependent upon whether whole-brain or midline exclusion method–based lateralization was calculated, and in the former case the inclusion of the occipital and other midline regions often negatively influenced the lateralization scores. Results: For the lateralized patients categorized by Wada, fMRI laterality indices (LIs) were concordant with the Wada procedure results in 83.87% patients for the reading task, 83.33% patients for the auditory task, 76.92% patients for the verbal fluency task, and in 91.3% patients for the conjunction analysis. ![]() Different laterality scores were examined as a function of statistical threshold to investigate the sensitivity to threshold effects. This was compared with the Wada procedure using both whole-brain and midline exclusion–based analyses. Methods: fMRI language mapping was performed in patients with epilepsy (N = 40) using reading sentence comprehension, auditory sentence comprehension, and a verbal fluency task. ![]() Sources of discordance between fMRI and Wada lateralization are discussed with respect to specific patient examples. Two localization methods and four different metrics for quantifying activation within hemisphere are compared and validated with Wada testing. Purpose: This work examines the efficacy of functional magnetic resonance imaging (fMRI) for language lateralization using a comprehensive three-task language-mapping approach. ![]()
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