Late talking represents one of the most common reasons children under 3-years of age are referred for speech-language evaluations, impacting about 10%-20% of children in this age-group. Late talkers (LT) also share similarities with children diagnosed with developmental language disorder (DLD) at 4 - 5 years of age, endorsing the notion that shared neurobiological underpinnings might exist between these two clinical groups. However, little is known about the neural basis of late talking, yet is needed to better inform the design of efficacious therapies that address hallmark delays in syntax and vocabulary. For the DLD population, domain-general processes relating memory and language are being investigated in the parent grant, offering valuable testing ground for also advancing the current knowledge base regarding LT. The Procedural circuit Deficit Hypothesis (PDH) posits that relative strengths and weaknesses exist between procedural (impaired) and declarative (less impaired) memory systems. Structural abnormalities in connections between frontal brain regions and basal ganglia, with under activation and reduced connectivity also evident. However, cortical and subcortical regions in the temporal lobes, including hippocampus, might be impaired to a lesser degree.

This proposed research will use diffusion imaging to describe the neural basis (structural connectivity) of late talking and treatment-related change by way of the PDH. The investigators will gather data regarding LT before, after, and following a break in standard intervention for LT (e.g., parent coaching, direct therapy for children who are LT): LT treatment. The investigators will also include a "business as usual": LT no treatment as part of a highly feasible pragmatic design that leverages existing pipelines. The investigators will also include typically developing (TD) peers to inform development vs late talking. The central hypothesis is that treatment designed to improve syntax and vocabulary will change procedural and declarative networks in association with increases in language function and the degree of improvement may be associated with the underlying neurobiology of baseline syntax and vocabulary deficits.

Building on a robust history of recruitment and treatment of toddlers by the investigators' partnering sites, and the investigators' successful imaging partner, this project will enroll 30 LT (n=15 treatment; n=15 controls) and 15 TD peers. Aim 1 will establish the structural connectivity in LT and their TD peers between regions in the procedural learning and declarative networks. In Aim 2, the investigators will establish the neurobiological basis of treatment-related changes in LT only. The investigators examine potential changes in structural connectivity between regions of the procedural learning and declarative memory networks, and investigate whether treatment-related changes occur into the typical range (LT, TD). To meet the scientific goals, the investigators pair behavioral tools (syntax and vocabulary) with neuroimaging to describe co-occurring behavioral performance underlying learning and outcome, while also gathering parental and clinician qualitative data regarding treatment outcomes. This research will contribute novel insights into mechanisms underlying learning and impairment to offer a ground-breaking shift in the understanding of LT.