Description

Although the impact of developmental language disorder (DLD), a prevalent preschool disorder, can be mitigated through evidence-based and early interventions, little is known about the neural basis of DLD, especially in young children, yet is useful in the design of efficacious treatments. While much of the evidence has been furnished by studies examining domain-specific processes (language network), domain-general processes relating memory and language also offer valuable testing ground and present the opportunity to advance the current knowledge base. The Procedural circuit Deficit Hypothesis (PDH) posits that grammar deficits are explained by an impairment of procedural memory (rule learning, "knowing how"). This impairment is associated with structural abnormalities in connections between frontal brain regions and basal ganglia, with corresponding underactivation and reduced functional connectivity. However, the declarative memory system (semantic, "knowing what"), supported by cortical and subcortical regions in the temporal lobes, including hippocampus, is spared, acting as a compensatory mechanism to offset grammar deficits.

This proposed research will use neuroimaging (functional MRI and diffusion imaging) to describe the neural basis (functional and structural connectivity) of grammar learning and treatment-related change by way of the PDH. The investigators will gather critical data regarding grammar learning in preschoolers with DLD before, after, and following a break in intervention (computer-assisted treatment: DLD treatment; "business as usual": DLD no treatment) as part of a randomized controlled trial. The investigators will also include typically developing (TD) peers to inform development vs disorder. Our central hypothesis is that treatment designed to improve grammar learning will normalize the procedural learning network in association with increases in language function and that the degree of improvement may be associated with the underlying neurobiology of baseline grammar deficits.

Building on a robust history of recruitment and treatment of preschoolers with DLD, the investigators will enroll 184 preschoolers, 100 with DLD (n=50 treatment; n=50 no treatment controls) and 84 TD. Aim 1 will establish the relationship between functional and structural connectivity for preschoolers with DLD 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 DLD only. The investigators examine potential changes in functional and structural connectivity between regions of the procedural learning and declarative memory networks, and investigate whether treatment-related changes occur into the typical range (DLD and TD). To meet our scientific goals, the investigators pair behavioral tools (traditional grammar tools) with neuroimaging to describe co-occurring behavioral performance underlying learning and outcome. This research will contribute novel insights into mechanisms underlying learning and impairment to help advance the evidence-based management of DLD.