High-Resolution Diffusion Tractography Reveals Structural Asymmetries in the Language Network
Poster No:
1019
Submission Type:
Abstract Submission
Authors:
Lilit Dulyan1, Cesare Bortolami2, Michel Thiebaut de Schotten3, Stephanie Forkel4
Institutions:
1Radboud University, Nijmegen, Netherlands, 2University of Genoa, Genoa, Italy, 3Groupe d’Imagerie Neurofonctionnelle, Institut des Maladies Neurodégénératives- UMR 5293, CNRS, CEA, Bordeaux, France, 4Donders Institute for Brain Cognition Behaviour, Radboud University, Nijmegen, Gelderland
First Author:
Co-Author(s):
Michel Thiebaut de Schotten
Groupe d’Imagerie Neurofonctionnelle, Institut des Maladies Neurodégénératives- UMR 5293, CNRS, CEA
Bordeaux, France
Groupe d’Imagerie Neurofonctionnelle, Institut des Maladies Neurodégénératives- UMR 5293, CNRS, CEA
Bordeaux, France
Stephanie Forkel
Donders Institute for Brain Cognition Behaviour, Radboud University
Nijmegen, Gelderland
Donders Institute for Brain Cognition Behaviour, Radboud University
Nijmegen, Gelderland
Introduction:
The language connectome has evolved from the conventional arcuate fasciculus model to a complex and extensive network of white matter tracts that goes well beyond the traditional boundaries of Broca and Wernicke areas (Dick et al., 2014). These tracts have been described in both brain hemispheres, questioning the previously dominant perspective of language functional lateralisation solely in the left hemisphere. Relying on the most precise dataset currently openly available (7T HCP), we mapped the extended language network in the human brain to comprehensively capture its structural asymmetry and interindividual variability. The normative atlas will facilitate the study of the functional relevance of the pathways and shed light on brain recovery in the extended bilateral language network.
Methods:
The study involved 172 healthy participants (29.5 ± 3.6 years, 60.5% females) from the Human Connectome Project's (HCP) 7T diffusion-weighted imaging (DWI) datasets (Vu et al., 2015). Data underwent preprocessing using the HCP default pipeline (v3.19.0; Glasser et al., 2013), addressing field, motion, and geometric distortions with FSL's TOPUP and EDDY functions (Andersson & Sotiropoulos, 2016). Whole-brain fibre orientation distribution (FOD) estimation used StarTrack software (https://www.mr-startrack.com) in the native DWI space. Spherical deconvolutions employed a damped Richardson-Lucy algorithm (Dell'acqua et al., 2010; Dell'Acqua & Tournier, 2019) with a fixed fibre response (α = 1.5 × 10–3 mm2 s−1) and a geometric damping parameter, involving 200 iterations.
For tractography, we set an absolute threshold (3x the spherical FOD of a grey matter isotropic voxel) and a relative threshold (8% of the maximum amplitude of the FOD; Thiebaut de Schotten et al., 2011). Streamline tractography used a modified Euler algorithm with a 35° angle threshold, 0.5 mm step size, and a 15 mm minimum streamline length (Dell'Acqua et al., 2013). The fixed absolute threshold, 0.0036, aligns with previous studies (Beyh et al., 2022; Thiebaut de Schotten et al., 2020), informed by post-mortem Klingler dissections. Structural connectome data was registered to the MNI space. Manual dissection of seven tracts in both hemispheres included FAT, IFOF, ILF, UF, and three AF segments. Microstructural indices (HMOA) and macro structural measurements (tract count, TC and volume , VC) were extracted for each tract. The lateralisation index (LI) was calculated as (right-left)/(right+left), with negative values indicating left lateralisation, positive values indicating right lateralisation, and an LI of 0 for bilateral distribution (Thiebaut de Schotten et al., 2011). One sample t-tests in R Studio compared each tract's LI to zero (Rstudio, 2020).
For tractography, we set an absolute threshold (3x the spherical FOD of a grey matter isotropic voxel) and a relative threshold (8% of the maximum amplitude of the FOD; Thiebaut de Schotten et al., 2011). Streamline tractography used a modified Euler algorithm with a 35° angle threshold, 0.5 mm step size, and a 15 mm minimum streamline length (Dell'Acqua et al., 2013). The fixed absolute threshold, 0.0036, aligns with previous studies (Beyh et al., 2022; Thiebaut de Schotten et al., 2020), informed by post-mortem Klingler dissections. Structural connectome data was registered to the MNI space. Manual dissection of seven tracts in both hemispheres included FAT, IFOF, ILF, UF, and three AF segments. Microstructural indices (HMOA) and macro structural measurements (tract count, TC and volume , VC) were extracted for each tract. The lateralisation index (LI) was calculated as (right-left)/(right+left), with negative values indicating left lateralisation, positive values indicating right lateralisation, and an LI of 0 for bilateral distribution (Thiebaut de Schotten et al., 2011). One sample t-tests in R Studio compared each tract's LI to zero (Rstudio, 2020).
Results:
The examination of seven tracts engaged during language processes unveils intriguing nuances. The long arcuate fasciculus and the ILF exhibit a pronounced inclination towards left lateralization (Figure 1). The IFOF and the FAT, manifest significant leftward asymmetry solely in the HMOA lateralization index (t(171)=-8.34, p<.0008 and t(171)=-5.68, p<.0008, respectively).
The posterior arcuate fasciculus (AFp) emerges as the only bilateral tract, exhibiting symmetry in hemisphere-specific microstructure and volume (Figure 1). Conversely, the UF and the anterior arcuate fasciculus (AFa) demonstrate a predilection for right lateralisation.
The posterior arcuate fasciculus (AFp) emerges as the only bilateral tract, exhibiting symmetry in hemisphere-specific microstructure and volume (Figure 1). Conversely, the UF and the anterior arcuate fasciculus (AFa) demonstrate a predilection for right lateralisation.
Conclusions:
This atlas, covering tracts implicated in language processes, has considerable potential to improve the accuracy of localizing white matter lesions linked to language disorders. Illuminating the nuanced interplay of structural asymmetries within the language network, our findings provide a foundational understanding that could pave the way for more precise interventions and therapies in the field of language-related neurological conditions. All data will be openly available.
Language:
Language Other 1
Neuroanatomy, Physiology, Metabolism and Neurotransmission:
Anatomy and Functional Systems
White Matter Anatomy, Fiber Pathways and Connectivity 2
Neuroinformatics and Data Sharing:
Brain Atlases
Novel Imaging Acquisition Methods:
Diffusion MRI
Keywords:
Hemispheric Specialization
Open Data
Tractography
White Matter
Other - Structural Asymmetry, Language
1|2Indicates the priority used for review
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