The neurocognition of procedural and declarative memory in dyslexia and S-RCD

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Reading proficiently is a critical skill. Nevertheless, about 25-30% of children are poor readers. Thus, the need to understand how individuals read and comprehend text is critical. A widely accepted developmental model of reading, the Simple View, demarcates reading as consisting of lower-level (phonemic decoding, i.e., orthographic-to-phonological conversions) and higher-level (comprehension) skills, with each level associated with different types of reading difficulties (RD). Those with dyslexia (DYS) show lower-level deficits, with poor phonological processing thought to play an important explanatory role in their impaired decoding abilities. Recently, interest has focused on basic learning mechanisms that may underlie DYS, including the role of procedural and declarative learning and memory. Evidence suggests that procedural memory is poor in DYS, but that declarative memory may be intact. In contrast to DYS, children with Specific Reading Comprehension Deficits (S-RCD) read words quickly and accurately, but struggle with the higher-level skill of reading comprehension. Studies of S-RCD indicate poor semantic processing despite adequate phonological processing/decoding, as well as neurobiological anomalies of the medial temporal lobe (a structure associated with declarative memory) while reading low frequency words. These findings suggest that declarative memory may be weak in S-RCD. Our overarching goal is to explore the behavioral and neural correlates of learning in declarative and procedural memory systems through comparison of DYS, S-RCD, and typically developing readers and examination of how these two memory systems relate to decoding and reading comprehension more generally. We hypothesize (Aim 1) that DYS will show weaknesses in procedural but not declarative learning, while S-RCD may show the opposite. These differences will also be reflected in neurobiological alterations in functional patterns underlying each system. We also hypothesize (Aim 2) more broadly that when decoding and reading comprehension are examined on a continuum, behavioral and neural indices of declarative/procedural memory will differentially predict the two reading skills. This line of research represents relatively new and uncharted territory in understanding RD, especially S-RCD, and may in the long run help elucidate better treatments for those with reading difficulty, which is a significant public health concern. Ultimately, our plan is to build on this exploratory project to pursue R01 funding.