To investigate speech in the developing brain, 94 children aged 4 to 7 years old were scanned using diffusion weighted imaging (DWI) magnetic resonance imaging. To increase sample size and performance variability, we included children with ADHD from a larger ongoing study (n = 47). Each child completed the Syllable Repetition Task (SRT), a validated measure of phoneme articulation. DWI data were modeled using restriction spectrum imaging to measure restricted and hindered diffusion properties in gray and white matter. We analyzed the diffusion data using whole brain analysis and automated fiber quantification (AFQ) analysis to establish tract profiles for the six fiber pathways thought to be important for supporting speech development. In the whole brain analysis, we found that SRT performance was associated with restricted diffusion in left and right inferior frontal gyrus, left and right pars opercularis, right pre-supplementary and supplementary motor area, and left and right cerebellar gray matter (p < 0.005). Age moderated these associations in left pars opercularis and the frontal aslant tract (FAT), but only the cerebellar findings survived a cluster correction. Analyses using AFQ highlighted differences in high and low performing children along specific tract profiles, most notably in left but not right FAT, in left and right superior longitudinal fasciculus III, and in the cerebellar peduncles. These findings suggest that individual differences in speech performance are reflected in structural gray and white matter differences as measured by restricted and hindered diffusion metrics, and offer important insights into developing brain networks supporting speech in very young children.

The heated debate regarding bilingual cognitive advantages remains ongoing. While there are many studies supporting positive cognitive effects of bilingualism, recent meta-analyses have concluded that there is no consistent evidence for a bilingual advantage . In this article we focus on several theoretical concerns. First, we discuss changes in theoretical frameworks, which have led to the development of insufficiently clear theories and hypotheses that are difficult to falsify. Next, we discuss the development of looking at bilingual experiences and the need to better understand language control. Last, we argue that the move from behavioural studies to a focus on brain plasticity is not going to solve the debate on cognitive effects, especially not when brain changes are interpreted in the absence of behavioural differences. Clearer theories on both behavioural and neural effects of bilingualism are needed. However, to achieve this, a solid understanding of both bilingualism and executive functions is needed first.