Language Exposure Relates to Structural Neural Connectivity in Childhood

Abstract

Neuroscience research has elucidated broad relationships between socioeconomic status (SES) and young children's brain structure, but there is little mechanistic knowledge about specific environmental factors that are associated with specific variation in brain structure. One environmental factor, early language exposure, predicts children's linguistic and cognitive skills and later academic achievement, but how language exposure relates to neuroanatomy is unknown. By measuring the real-world language exposure of young children (ages 4-6 years, 27 male/13 female), we confirmed the preregistered hypothesis that greater adult-child conversational experience, independent of SES and the sheer amount of adult speech, is related to stronger, more coherent white matter connectivity in the left arcuate and superior longitudinal fasciculi on average, and specifically near their anterior termination at Broca's area in left inferior frontal cortex. Fractional anisotropy of significant tract subregions mediated the relationship between conversational turns and children's language skills and indicated a neuroanatomical mechanism underlying the SES "language gap." whole-brain analyses revealed that language exposure was not related to any other white matter tracts, indicating the specificity of this relationship. Results suggest that the development of dorsal language tracts is environmentally influenced, specifically by early, dialogic interaction. Furthermore, these findings raise the possibility that early intervention programs aiming to ameliorate disadvantages in development due to family SES may focus on increasing children's conversational exposure to capitalize on the early neural plasticity underlying cognitive development. Over the last decade, cognitive neuroscience has highlighted the detrimental impact of disadvantaged backgrounds on young children's brain structure. However, to intervene effectively, we must know which proximal aspects of the environmental aspects are most strongly related to neural development. The present study finds that young children's real-world language exposure, and specifically the amount of adult-child conversation, correlates with the strength of connectivity in the left hemisphere white matter pathway connecting two canonical language regions, independent of socioeconomic status and the sheer volume of adult speech. These findings suggest that early intervention programs aiming to close the achievement gap may focus on increasing children's conversational exposure to capitalize on the early neural plasticity underlying cognitive development.

White matter in infancy is prospectively associated with language outcome in kindergarten

“…Our findings indicate that these relationships may be, in part, explained by pre-existing brain structure from as early as infancy, consistent with the notion that structural connectivity precedes functional development (Saygin et al, 2016). Moreover, the specificity of our findings within the posterior segment of the left arcuate fasciculus in infancy shares anatomical overlap with previous findings in preschoolers (Romeo et al, 2018). This novel evidence that structural organization of white matter in infancy is prospectively associated with language skills in kindergarten suggests that the structural foundation for the arcuate fasciculus, established within the first two years of life, contributes to the developmental trajectory of language and the corresponding brain-behavioral relationships observed in school-age children and adults.…”

“…Our findings linking the arcuate fasciculus in infancy with subsequent phonological awareness and vocabulary knowledge directly align with key constructs implicated in previous studies of school-age children (Lebel and Beaulieu, 2009;Reynolds et al, 2019;Saygin et al, 2013). These relationships also account for factors pertaining to the home environment, in line with the previously identified role of the left arcuate fasciculus in mediating the relationship between environmental exposure to language (number of conversational turns) and language skills among 4-6 year olds (Romeo et al, 2018). Our findings indicate that these relationships may be, in part, explained by pre-existing brain structure from as early as infancy, consistent with the notion that structural connectivity precedes functional development (Saygin et al, 2016).…”

“…This pathway has also been directly associated with language exposure (i.e., the number of conversational turns in dialogic interaction) independent of socioeconomic status (Romeo et al, 2018). In fact, structural organization of the left arcuate fasciculus was observed to mediate the well-known relationship between language exposure and language skills among four-to six-year-old children (Romeo et al, 2018). Therefore, languagerelated white matter organization has been indicated as a specific and crucial mechanism underlying language abilities; however, there has yet to be any indication of how early white matter in infancy may predict subsequent language abilities at the school age.…”

“…Relationships between white matter and language are specific and independent of socioeconomic factors according to evidence acquired at the school age (Romeo et al, 2018), but have yet to be investigated starting from infancy. Among school-age children, structural organization of the left arcuate fasciculus has been positively linked with language skills in domains including phonological awareness and vocabulary knowledge (Lebel and Beaulieu, 2009), and cross-sectional links with phonological awareness have been shown as early as three years of age (Reynolds et al, 2019).…”

“…Among school-age children, structural organization of the left arcuate fasciculus has been positively linked with language skills in domains including phonological awareness and vocabulary knowledge (Lebel and Beaulieu, 2009), and cross-sectional links with phonological awareness have been shown as early as three years of age (Reynolds et al, 2019). This pathway has also been directly associated with language exposure (i.e., the number of conversational turns in dialogic interaction) independent of socioeconomic status (Romeo et al, 2018). In fact, structural organization of the left arcuate fasciculus was observed to mediate the well-known relationship between language exposure and language skills among four-to six-year-old children (Romeo et al, 2018).…”