Syntactic development and its interplay with word processing and working memory in preschoolers' brain: An fNIRS longitudinal study

Understanding how children acquire syntactic structures from a limited set of grammatical rules and use them creatively to convey meaning has been a longstanding interest for scientific communities. Previous studies on syntactic development have revealed its close correlation with the development of vocabulary and working memory. Our study sought to elucidate how the relations between syntactic processing, word processing, and working memory were instantiated in the brain, and how earlier neural patterns might predict language abilities one year later. We employed functional near-infrared spectroscopy to examine among preschool children (N=50, M_age=61.5 months) the neural activation associated with processing sentences of varying syntactic complexities, as well as tasks assessing word comprehension and working memory. The results revealed greater brain activation in the left inferior frontal gyrus (IFG) for syntactically complex as compared to simple sentences, and the activation magnitude was correlated with working memory. There was also a link between neural activity for sentence comprehension and word comprehension in bilateral superior temporal regions (STG). Moreover, the inter-regional and inter-hemispheric connectivity of IFG and STG/MTG could successfully predict children's future language comprehension one year later. The findings provide new insights into how the brain supports syntactic development and its interplay with word processing and working memory.