Slide Slam H11
Studying the anatomical basis of language lateralisation using white matter connectometry
Ieva Andrulyte1, Christophe de Bezenac1, Peter Taylor2, Simon Keller1; 1University of Liverpool, 2Newcastle University
Introduction: In approximately 90% of the general population language depends on specialised brain networks in the left cerebral hemisphere. Some people have “atypical” language representation (right hemisphere or bilateral lateralisation), which is more prevalent in left-handers (Mazoyer et al, 2014). The reasons for this hemispheric specialisation are unknown. It has been suggested that brain structural asymmetry is related to functional language lateralisation. Studies using structural magnetic resonance imaging (MRI) investigations have reported a leftward asymmetry of language relevant brain regions, including the inferior frontal gyrus, superior temporal gyrus, and interconnecting white matter tracts such as the arcuate fasciculus (Catani et al, 2007; Barrick et al, 2005; Keller et al, 2007). However, few studies have used whole-brain diffusion MRI approaches to investigate how white matter architecture is related to functional language lateralisation in healthy people. In the present study, we mapped the relationship between whole-brain white matter fibre quantitative anisotropy (QA) and functional MRI determined language lateralisation in a large cohort of healthy people. Methods: We investigated 188 healthy young (22-35 years) adult participants from the Human Connectome Project (HCP) database. All participants underwent diffusion and functional MRI. The functional MRI language task used was developed by Binder and colleagues (2011) and consists of two runs that each interleave four blocks of a story task and four blocks of a math task. Functional activation associated with language comprehension was determined using a story-math contrast. Hemispheric language comprehension lateralisation was determined using a laterality index (LI) for each participant’s activated regions (Z > 1.96, corresponding to two-tailed uncorrected P < 0.05). The relationship between quantitative anisotropy (QA) and a continuous measure of LI was assessed using a DSI Studio Connectometry analysis, which was based on a deterministic fibre tracking algorithm and uses QA as the termination index (Yeh et al, 2016). Results: Based on LIs, participants were classified as left (119), right (11), and bilateral (58) lateralised individuals. Both left-hemisphere dominant and atypically-lateralized individuals showed activations in classical language areas: Broca’s area, Wernicke’s area, angular gyrus, posterior cingulate cortex, and lateral prefrontal cortex. Across groups, LIs were significantly (FDR < 0.05) positively correlated with QA in the forceps minor, left inferior fronto-occipital fasciculus, left uncinate fasciculus, and the cingulum bilaterally. The QA of the right fornix and right uncinate fasciculus was negatively correlated with LIs. Conclusion: This is the first white matter connectometry study of language lateralisation in healthy individuals. Using this novel connnectometry approach based on correlational tractography paradigm we report that language lateralisation is associated with white matter QA – a potential marker of connectivity strength – in anterior commissural regions and focal regions of long association fibres.