Neural Substrates of Word Retention and Generalization in Toddlers

PROJECT SUMMARY Infants and young children amass a vocabulary at a remarkable pace during the first 3 years. The size of vocabulary, and the rate of its growth predict future outcomes including academic achievement. Research on vocabulary development has largely focused on the cognitive processes underlying how young children learn new words, but we know remarkably little about the processes that support young children's retention of words over long delays to eventually become integrated into their lexicon. The examination of the neural processes supporting young children's retention will shed new light on contributing processes. We propose that the hippocampus enables learning and initial retention of the arbitrary association between words and their referents, but that additional cortical mechanisms in the anterior medial temporal lobe and medial prefrontal cortex are critical to respectively support longer retention and abstraction of meaning across multiple exposures. Further, we propose that opportunities to repeat and generalize which present in the child's environment are particularly likely to engage these cortical mechanisms in young children. Finally, we propose that neural activations capture processes underlying individual differences in vocabulary development. We developed novel functional Magnetic Resonance Imaging (fMRI) experimental paradigms that are appropriate for use in toddlers ages 25 to 35 months, a period during which toddlers learn hundreds of words. We will leverage targeted memory reactivation occurring during natural nocturnal sleep to elucidate neural mechanisms contributing to word retention and to predict vocabulary size and growth between 2 and 3 years of age. Relevance for Public Health: The acquisition of a vocabulary is critical for communication and understanding, and its size and growth predict various outcomes, including reading ability. Language acquisition is impaired in several neurodevelopmental disorders underscoring that a characterization of memory and vocabulary development is key to understanding adaptive functioning in various populations of children. This research will contribute to provide a stronger conceptual, empirical, and methodological foundation for examining populations of children who exhibit altered language development and memory difficulties due to a variety of conditions (e.g., Autism Spectrum Disorder, Down's Syndrome).