PROJECT SUMMARY/ABSTRACT Although language abilities vary across the autism spectrum, the majority of children with Autism Spectrum Disorder (ASD) have language deficits that emerge early in life and have long lasting negative impacts on other domains of functioning. Previous work suggests that differences in how the brain processes language (i.e., reduced activation/response and functional connectivity) may contribute to the development of language deficits in ASD. However, only a handful of neuroimaging studies have explored the neural bases of language processing in children with ASD during the preschool years, a sensitive period in language development. Additionally, all of these studies measured brain response while children were asleep and socially-isolated, a context that is not generalizable to real-world language environments. The proposed research project will build upon the findings of these foundational neuroimaging studies by investigating how the brains of preschoolers with and without ASD function during a live social interaction. We will use functional near-infrared spectroscopy (fNIRS), a sensory-friendly neuroimaging method, to measure children’s brain activity during two conditions – a live condition and a recorded condition. During the live condition, a live experimenter will interact with the child by reading him/her a scripted story from an illustrated book. During the recorded condition, the child will listen to a recording of a scripted story while viewing illustrations on a screen. A sample of 50 children with ASD and 50 typically developing (TD) controls, 36- to 60-months-old, will be used to address three research aims. The first aim is to determine how live social interaction modulates brain response to language in preschoolers with and without ASD. We hypothesize that TD controls will have greater brain response during the live condition compared to the recorded condition, while children with ASD will have similar brain response across both conditions. The second aim is to examine whether functional connectivity (FC) during a live social interaction (i.e., the live condition) differs between preschoolers with and without ASD. We hypothesize that the ASD group will have reduced inter- and intra-hemispheric FC. The third aim is to investigate the relation between measures of brain function (brain response and FC) and language abilities, communication skills, and autism severity. We hypothesize that greater brain response and FC during the live condition will be related to better language abilities and communication skills, but lower autism severity. Findings from this innovative project will demonstrate how the brains of preschoolers with and without ASD, an understudied age group, function during everyday social interactions. Exploring individual differences in brain function will elucidate the neural mechanisms underlying language deficits and heterogeneous language outcomes in ASD. Clinically, findings may provide in...