Abstract 3807: Threshold Effects on Language Lateralization

Abstract

Background: Vascular lesion patients may have atypical language networks (Vikingstad et al. 2000). When evaluating language function in vascular lesion patients, the threshold of significance at which functional activations are analyzed may lead to differences in the lateralization index (LI) calculated. We examine the effect of various thresholds on language LIs in vascular lesion patients and control subjects. We further aim to compare language LIs in these two groups and to analyze patient LIs for correlations with lesion activation distance (LAD). Methods: Structural and functional images were collected from 29 vascular lesion patients and 14 normal controls while they performed language tasks in the scanner such as word generation and text comprehension. Left Hemisphere, frontal lobe (Broca’s), and temporal lobe (Wernicke’s) masks as well as masks of their homologous counterparts were created based on the language network identified in a meta-analysis of language studies by Vigneau et al. 2006. LI was calculated for each subject for each task on which data was acquired using each of the six masks at four different thresholds of statistical significance. Patient LIs were further analyzed for correlations with LAD to Broca’s and Wernicke’s areas. Results: Vascular lesion patients tend to display bilateral or left-lateralized language functions. At the group level, increasing threshold value tended to shift LIs toward left-lateralization. Relative to controls, patients with vascular lesions appear to lateralize language functions necessary for word generation to a lesser degree, which was trending toward significance. Pooled data from visual receptive language tasks shows association between computed LI values for the frontal lobe and Wernicke's LAD, which was significant at lower thresholds. Conclusions: Variable thresholding may cause reclassification of some patients based on LI, and higher thresholds tend to shift LI towards left-lateralization. The association observed between frontal lobe LI values and LAD to Wernicke’s area suggest that for these patients LAD to Wernicke’s may be a significant factor in lateralization at lower thresholds. These factors may be important if using LI in presurgical planning. Differences in the degree of lateralization between vascular lesion patients and controls may be due to long-term brain reorganization.