The brain structure during language development: neural correlates of sentence comprehension in preschool children

Language skills increase as the brain matures and language specialization is linked to the left hemisphere. Among distinct language domains, sentence comprehension is particularly vital in language acquisition and, by comparison, requires a much longer time-span before full mastery in children. Although accumulating studies have revealed the neural mechanism underlying sentence comprehension acquisition, the development of the brain’s gray matter and its relation to sentence comprehension had not been fully understood. This thesis employs structural magnetic resonance imaging and diffusion-weighted imaging data to investigate the neural correlates of sentence comprehension in preschoolers both cross-sectionally and longitudinally. The first study examines how cortical thick- ness covariance is relevant for syntax in preschoolers and changes across development. Results suggest that the cortical thickness covariance of brain regions relevant for syntax increases from preschoolers to adults, whilst preschoolers with superior language abilities show a more adult-like covariance pattern. Reconstructing the white matter fiber tract connecting the left inferior frontal and superior temporal cortices using diffusion-weighted imaging data, the second study suggests that the reduced cortical thickness covariance in the left frontotemporal regions is likely due to immature white matter connectivity during preschool. The third study then investigated the cortical thickness asymmetry and its relation to sentence comprehension abilities. Results show that longitudinal cortical thick- ness asymmetry in the inferior frontal cortex was associated with improvements in sentence comprehension, further suggesting the crucial role of the inferior frontal cortex for sentence comprehension acquisition. Taken together, evidence from gray and white matter data provides new insights into the neuroscientific model of language acquisition and the emergence of syntactic processing during language development