Early life stress and socioeconomic variation as determinants of language-related neurodevelopment

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Early language experience shapes neural systems that support the development of increasingly complex language abilities, allowing children to adapt to their unique environments (e.g., Werker & Hensch, 2015). Yet, how early variation (e.g., in timing, quality, and quantity of input) influences the development of these neural systems, and implications for long-term language outcomes, are not well understood (Pierce et al., 2017a,b). Systematic comparisons between groups with known differences in the early language environment (e.g., bilingual, monolingual, international adoptees; Pierce et al., 2014; 2015) have been used to test pathways between early environmental variation and language outcomes via neurodevelopmental change (Pierce et al., 2017a,b). However for many children, systematic ways that early experiences differ have not been identified. For example, while socioeconomic status (SES) predicts children's language abilities (e.g., Hoff, 2003), sources of variability within a socioeconomically diverse context, and neurodevelopmental pathways leading to disparate language outcomes, are not well understood. Evidence from mother-infant dyads suggests that maternal stress, within a low-SES context, is associated with language behaviours and caregiver-child interactions during infancy (Pierce et al., 2020). Behaviours have also been associated with electroencephalography (EEG) patterns that a) vary as a function of stress (Pierce et al., 2019), and b) predict language outcomes (Benasich et al., 2008). Results suggest how early variation in a socioeconomically diverse context could be used to test interactions between early input and neurodevelopment, yet considerable work remains. I propose a novel multidisciplinary approach, using developmental neuroscience tools and home language recordings, to: 1) characterize sources of early variation (e.g., stress) in socioeconomically diverse contexts, 2) map early variation to specific neural processes underlying language development, and 3) test whether these neural processes mediate associations between early variation and language outcomes. I will also 4) probe individual differences (e.g., sex; physiological metrics of stress) as moderators of neurodevelopmental change, and 5) explore how language development interacts with other developing systems. Here I use our strong understanding of language development, along with dimensional frameworks for defining adversity, as tools to illuminate mechanisms of neuroplasticity (e.g., how early variation exerts long-lasting experience-dependent neural change). I make clear predictions for why specific language features might be affected by early input variation, and how these impact language outcomes over time. This will broadly inform our understanding of mechanistic links between early variability and language outcomes - particularly in the critically lacking area of socioeconomic variability - and will reveal fundamental properties of brain development.