The Clinical Utility of Transcranial Magnetic Stimulation in Determining Hemispheric Dominance for Language: A Magnetoencephalography Comparison Study

Abstract

Purpose: Transcranial magnetic stimulation (TMS) has recently emerged as a noninvasive alternative to the intracarotid sodium amytal (Wada) procedure for establishing hemispheric dominance (HD) for language. The accuracy of HD determined by TMS was examined by comparing against the HD derived by magnetoencephalography (MEG), a prominent clinical technique with excellent concordance with the Wada procedure. Methods: Sixty-seven patients (54 patients ≤18 years) underwent language mapping with TMS and MEG as part of clinical epilepsy and tumor presurgical assessment. Language was mapped in MEG during an auditory word recognition paradigm, and a laterality index was calculated using the number of dipoles and their spatial extent in the two hemispheres. Transcranial magnetic stimulation language mapping was performed as patients performed a naming task, and TMS-induced speech disruptions were recorded during 5-Hz TMS applied to anterior and posterior language cortices. Transcranial magnetic stimulation laterality index was estimated using the number and type of speech disruption in the language regions of each hemisphere. Results: Transcranial magnetic stimulation and MEG estimates of HD were concordant in 42 (63%) patients, resulting in a sensitivity of 74% and a specificity of 72%. The overall accuracy of TMS was 73%, equivalent to an odds ratio of 7.35. Conclusions: In this first large-scale comparative study in a clinical population, we demonstrate that TMS is a safe and reliable noninvasive tool in determining HD for language. Improving the accuracy of TMS by optimizing TMS parameters and improving task choice will further facilitate the use of TMS to characterize language function, especially in pediatrics.

Concordance Between Transcranial Magnetic Stimulation and Functional Magnetic Resonance Imaging (MRI) Derived Localization of Language in a Clinical Cohort

“…The overall accuracy of TMS was found to be 73%, equivalent to an odds ratio of 7.35. 9 Thus, the current TMS language mapping protocol has similar performance metrics when compared to functional MRI and magnetoencephalography, both wellestablished noninvasive language mapping techniques.…”

“…But when compared with both ON MRI and VG MRI findings, the hemispheric dominance determined by TMS underestimated the incidence of left dominance (Tables 1, 2, and 7). We have previously examined the accuracy of hemispheric dominance determined by TMS by comparing against the hemispheric dominance derived by magnetoencephalography, 9 a technique with excellent concordance with the Wada procedure. In a cohort of 67 patients (54 18 years), magnetoencephalography identified 85% of patients to be left hemisphere dominant as opposed to TMS which found 69% of patents to be left hemisphere dominant, a finding similar to that reported here for functional MRI and TMS.…”

“…Similar to functional MRI, TMS-induced speech errors are also amenable to calculating a laterality index (LI). 9 For TMS, the laterality index (LI) was calculated as E left -E right / E left þ E right , where E left was the total number of speech errors in the left hemisphere and E right was the total number of speech errors in the right hemisphere. Values 1.0 to 0.1 indicated left hemisphere dominance (HD), -1.0 to -0.1 indicated right hemisphere dominance and values between -0.1 and þ0.1 were considered a balanced bilateral representation of language.…”

“…Language cortices including the pars triangularis (Brodmann area [BA] 45), pars opercularis (BA 44), and parts of the ventral premotor cortex (BA 6) in both hemispheres have been identified using this technique. [6][7][8][9] TMS is also successful in localizing primary and secondary auditory cortices in the temporal lobe (BA 41,42,22,and 21), as well as the inferior parietal lobule, supramarginal gyrus (BA 40), angular gyrus (BA39), and parietal operculum (BA 43). [6][7][8][9][10][11][12][13] Thus, brain areas engaged in semantic and phonologic processing, motor planning, and articulation can be identified using TMS in both healthy and clinical cohorts.…”

A Functional Magnetic Resonance Imaging Approach for Language Laterality Assessment in Young Children

“…Second, there is a relatively large incidence of atypical language lateralization among patients with epilepsy, including children (8,9), which is thought to be related to the chronic nature of the condition (10). The intracarotid amobarbital test has long been considered as the gold standard for assessment of language lateralization, but since that procedure is highly invasive and stressful (11), other methods are investigated, including magnetoencephalography [e.g., (12)], transcranial magnetic stimulation [e.g., (13,14)], and functional transcranial doppler [e.g., (15)].…”