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 underactivation 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. We will gather data regarding LT before, after,
and following a break in a well-known parent-led therapy (Target WordTM-The Hanen Program® for Parents of
Children who are LT: LT treatment; “business as usual”: LT no treatment) as part of a highly feasible RCT that
leverages existing pipelines. We will also include typically developing (TD) peers to inform development vs late
talking. Our 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 Hanen Centre®, and our
successful imaging partner, we 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, we will establish the neurobiological basis of treatment-related changes in LT
only. We 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 our scientific goals, we pair behavioral tools (syntax and vocabulary) with neuroimaging to
describe co-occurring behavioral performance underlying learning and outcome, while also gathering parental
and clinican qualitative data regarding treatment outcomes. This research will contribute novel insights into
mechanisms underlying learning and impairment to offer a groundbreaking shift in our understanding of LT.