V6. Language lateralization – A comparison of three non-invasive methods in healthy adults

Abstract

Introduction Language lateralization is crucial in the presurgical evaluation of epilepsy patients to avoid damage to eloquent cortex and to diminish risks of post-surgical language problems. Several non-invasive tools exist to determine language dominance. The gold standard is the invasive Wada-Test. We applied three different, non-invasive methods for language lateralization in healthy adults to determine their concordance. Dichotic listening (DL) test, functional transcranial Dopplersonography (fTCD) and functional magnetic resonance imaging (fMRI) were used. Additionally, acoustically evoked potentials (AEP) were analyzed to prove normal physiology of hearing. Methods fTCD measures the task-dependant relative blood flow velocity changes in both medial cerebral arteries (word generation). Hemispheric differences are calculated and a laterality index (LI) with its standard error of the mean (SEM) are calculated with the program Average©. The fMRI data using the same word generation paradigm were analyzed using Feat of the FSL© package. The calculated fMRI Images were coregistered to the anatomical images. A laterality index was calculated for each subject. DL was used by presenting two rhyme words simultaneously to both ears. The ear contralateral to the language dominant side usually recognizes more words. A leftsided dominance thus leads to more right ear points (REP) and vice versa. A Lambda-Index is given. In all modalities, a positive LI means left-sided language dominance. Results Twenty-three subjects (Age range: 17–39 years, mean 25.6 ± 4.7 SD; 14 female) underwent all three methods. 21 were strongly right-handed (EHI ≥ 70). In 17/23 (74%) fTCD and fMRI were condordant (16 left, 1 no lateralization). Notably, seven subjects had low activation during fMRI which did not lead to lateralization while those seven however had left lateralization during fTCD. In 15 cases (65%) both fTCD and DL lateralized to the left side. Four subjects lateralized to the left during fTCD and showed no lateralization in DL, either due to no lateralization pattern or high stimulus domincane. Two were typical in fTCD and atypical in DL. Only one subject failed to lateralize during fTCD and showed typical lateralization in DL. The correlation for fTCD and fMRI was medium (r = .454, p = .029). DL results did not correlate with either fTCD or fMRI. AEP showed no abnormalities in hearing. The AEP did not correlate with either DL, fTCD or fMRI. Discussion FTCD, fMRI and DL are easily applicable in healthy participants and mostly concordant for lateralization of language dominance. However, language lateralization was achievd in most patients with fTCD, supporting its value for clinical routine. Arguably, the direct feedback of the examiner during fTCD might have enhanced activation and motivation. This study calls for close monitoring and feedback enhancing during DL and fMRI. For better comparison of DHT and fMRI a Wernicke-paradigm should be used in future studies.