Manifold lateralisation and variability in the language connectome at 7T.

Area of Science:

• Neuroscience
• Neuroimaging
• Brain Anatomy

Background:

• Language lateralisation is a key feature of brain function, typically associated with left hemisphere specialization.
• The precise structural basis and individual variability of this hemispheric asymmetry in language networks remain incompletely understood.

Purpose of the Study:

• To investigate the structural underpinnings of language lateralisation using advanced diffusion MRI techniques.
• To characterize the architecture of hemispheric asymmetry in key language-related white matter tracts.
• To explore individual differences in structural lateralisation patterns.

Main Methods:

• Utilized ultra-high-field 7T diffusion MRI data from 172 Human Connectome Project participants.
• Reconstructed seven language-recruited white matter tracts.
• Employed a novel Variability Index, Bayesian inference, and manifold learning to analyze tract architecture and asymmetry.

Main Results:

• Individuals exhibit a continuous spectrum of structural lateralisation, not discrete left, right, or bilateral phenotypes.
• Specific tracts demonstrate consistent directional asymmetry: leftward for arcuate long segment, inferior longitudinal fasciculus, and frontal aslant tract; rightward for anterior arcuate segment and uncinate fasciculus.
• Significant microstructural variability exists within tracts, with some showing greater dispersion in one hemisphere.

Conclusions:

• Hemispheric specialisation for language represents a graded, continuous connectome rather than a strictly dichotomous distribution.
• The brain balances conserved structural patterns with individual flexibility in language network lateralisation.
• Structural lateralisation patterns are independent of handedness and language performance in the studied population.