Assessing the Early Lateralization of White Matter in the Infant Language Network

Area of Science:

• Neuroscience
• Developmental Neuroscience
• Cognitive Neuroscience

Background:

• Neural language development relies on maturing frontal and temporal language centers and their white matter connections.
• Leftward asymmetry in white matter tracts is observed by age five and maintained into adulthood, supporting mature language function.
• The presence and relation of this laterality in infancy to early language acquisition remain unclear.

Purpose of the Study:

• To investigate longitudinal changes in white matter microstructure and macrostructure of language (arcuate fasciculus [AF], uncinate fasciculus [UF]) and motor (corticospinal tract [CST]) pathways in typically developing infants.
• To test the hypothesis that left hemisphere language tracts mature faster in infancy, indicating an early left-hemisphere bias for language.
• To examine concurrent bilateral maturation of non-motor tracts.

Main Methods:

• Analysis of longitudinal data from 114 typically developing infants (0-24 months) from the HCP Baby Connectome Project.
• Measurement of fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), axial diffusivity (AD), probabilistic streamlines, and tract volume in bilateral AF, UF, and CST.
• Utilized linear mixed-effects modeling for developmental trajectories and reconstructed tracts in adult cohorts for comparison.

Main Results:

• All examined tracts showed rapid age-related microstructural maturation in infants, but no significant age-related increases in tract volume or streamline count.
• No significant sex-based differences were observed in any measures.
• Unlike adults, infants did not exhibit significant leftward asymmetry in AF or UF maturation rates, though the right UF had more streamlines.

Conclusions:

• While white matter tracts crucial for language demonstrate rapid microstructural maturation in infancy, significant leftward lateralization is not yet evident.
• This suggests that strong language-related lateralization may develop later, potentially coinciding with increased language skill acquisition or cortical lateralization in childhood.
• Future research should include other language tracts and extend data collection from infancy through childhood to track the emergence of functional language lateralization.