Temporal lobe white matter asymmetry and language laterality in epilepsy patients

Abstract

Recent studies using diffusion tensor imaging (DTI) have advanced our knowledge of the organization of white matter subserving language function. It remains unclear, however, how DTI may be used to predict accurately a key feature of language organization: its asymmetric representation in one cerebral hemisphere. In this study of epilepsy patients with unambiguous lateralization on Wada testing (19 left and 4 right lateralized subjects; no bilateral subjects), the predictive value of DTI for classifying the dominant hemisphere for language was assessed relative to the existing standard - the intra-carotid Amytal (Wada) procedure. Our specific hypothesis is that language laterality in both unilateral left- and right-hemisphere language dominant subjects may be predicted by hemispheric asymmetry in the relative density of three white matter pathways terminating in the temporal lobe implicated in different aspects of language function: the arcuate (AF), uncinate (UF), and inferior longitudinal fasciculi (ILF). Laterality indices computed from asymmetry of high anisotropy AF pathways, but not the other pathways, classified the majority (19 of 23) of patients using the Wada results as the standard. A logistic regression model incorporating information from DTI of the AF, fMRI activity in Broca’s area, and handedness was able to classify 22 of 23 (95.6%) patients correctly according to their Wada score. We conclude that evaluation of highly anisotropic components of the AF alone has significant predictive power for determining language laterality, and that this markedly asymmetric distribution in the dominant hemisphere may reflect enhanced connectivity between frontal and temporal sites to support fluent language processes. Given the small sample reported in this preliminary study, future research should assess this method on a larger group of patients, including subjects with bihemispheric dominance.

Distinct loci of lexical and semantic access deficits in aphasia: Evidence from voxel-based lesion-symptom mapping and diffusion tensor imaging

“…ROI-based analyses provide converging evidence for findings from the VLSM analyses, which is particularly relevant for the theoretical question tested regarding whether the posterior and anterior temporal lobes play different roles in lexical-semantic processing for production and comprehension. To quantify the integrity (i.e., fractional anisotropy (FA) value) of white matter pathways interconnecting the language network, we used DTI deterministic tractography (Ellmore et al, 2010;Harvey et al, 2013). We correlated pathway integrity with individual measures of relatedness and increasing relatedness effects to determine whether reduced structural connectivity accounts for behavior above and beyond the contribution from lesion location and/or total lesion volume.…”

“…Diffusion-weighted image volumes were then aligned to the individual's skull-stripped anatomical averaged T1-weighted MR image, and the gradient orientation vectors were rotated based on the individual angular motion parameters (Leemans & Jones, 2009). Diffusion tensor computations were carried out in native imaging space to preserve the reliability of calculated fiber tracts (Ellmore et al, 2010;Harvey et al, 2013).…”

“…Pathways were delineated in DTI Query v1.1 (Akers, Sherbondy, Mackenzie, Dougherty, & Wandell, 2004;Sherbondy, Akers, Mackenzie, Dougherty, & Wandell, 2005) using deterministic tractography methods (following Ellmore et al, 2010;Harvey et al, 2013). A "seed" region, consisting of one or more volumes of interest (VOI), was placed at known anatomical terminations of fiber tracts (Mori, Crain, Chacko, & van Zijl, 1999;Catani, Howard, Pajevic, & Jones, 2002).…”

A nested cortex parcellation combining analysis of MEG forward problem and diffusion MRI tractography

“…The study of the symmetry and the non-symmetry of the brain as performed in [10], could greatly benefit from our cortex parcellation to give important information about the correlations between structure and function. Finally, our nested cortex parcellation allow the use of structural benchmarks for the neural modelling.…”

Detection of temporal lobe epilepsy using support vector machines in multi-parametric quantitative MR imaging

“…White matter abnormalities have been detected with diffusion tensor imaging (DTI) in TLE patients [6,7,8], and DTI has been employed concurrently with functional MRI (fMRI) to perform language lateralization of TLE patients [9].…”