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Gray matter diffusion properties associated with new word learning
Poster Session A, Wednesday, September 30, 11:00 am - 1:00 pm, Wangari Maathai
Brenda Rapp1, Julie Loritsch2, Casey Vanderlip2, Robert Wiley3, Craig Stark2; 1Johns Hopkins University, 2University of California, Irvine, 3University of North Carolina, Greensboro
INTRODUCTION. The relationship between white matter micro-structure and cognition has been extensively studied across cognitive domains and populations. More recently, research has examined the relationship between grey-matter microstructure and cognition. Multi-shell imaging has supported analysis techniques beyond tensors, including neurite orientation and dispersion and density imaging (NODDI) and Mean Apparent Propagator (MAP) that provide estimates of extra- and intra-cellular cellular components and the free water diffusion within a voxel. Recent work has shown that these metrics, individually and in combination, can predict age and memory performance (e.g., Kimbler & Stark, 2025), potentially capturing independent microstructural information. To date, work using these metrics has largely focused on learning and memory, and primarily in neuropathology. Here, we examine its relevance to furthering our understanding of the neural mechanisms of new word learning in older and younger adults, in a paradigm involving learning the written, spoken and meaning properties of novel words over several weeks. METHODS. Healthy young and older adults (n=45) were tasked with learning the written, spoken forms, and meanings of 36 novel pseudo-words, in bi-weekly sessions over ~6 weeks. Behavioral measures of learning and retention were collected on each learning session. For this report we considered two learning measures: Early Learning and Extended Learning, corresponding to the amount of learning (for written, spoken and meaning components) on the first session and across the subsequent 4 sessions, respectively. Multi-shell DWI scanning was administered at multiple time-points during learning. DWI data were preprocessed using QSIPREP, and multiple diffusion models were applied, including diffusion tensor imaging, NODDI, and MAP MRI. Regression models were used to examine the relationship between Early and Extended Learning performance and 6 microstructural properties and their combination, for 8 bilateral, pre-defined ROIs; all results were corrected for multiple comparisons. RESULTS. First, validating our measures, we found that DWI metrics accurately distinguished younger from older adults, revealing widespread age-related microstructural changes across the brain during healthy aging. Early Learning. DWI metrics accurately distinguished early word-form learners and early meaning learners from their slower counterparts. Word Meaning: bilateral hippocampus and angular gyrus; Word Form: bilateral parahippocampal and lingual gyri. Extended Learning. DWI metrics, along with age, predicted orthographic, phonological, and semantic learning outcomes. Word Meaning: bilateral hippocampus and middle temporal gyrus; Word Form: parahippocampal gyrus. CONCLUSIONS. Across older and younger adults, analysis of the relationship between new word learning success and gray matter microstructural properties revealed associations both in early and later stages of learning. Learning success was related to gray matter microstructure in both subcortical (hippocampal) and cortical (parahippocampal, angular, middle temporal, lingual gyri) regions. These findings are consistent with the central claim of the complementary learning systems framework (McClelland, et al., 1995) that both systems play critical roles in learning. Additionally, there are some indications that different dimensions of lexical representation -word form and meaning- may make differential demands on different regions. More generally, the findings provide evidence of the utility of gray matter diffusion in the study of the neurobiology of language learning in the healthy brain.
Topic Areas: Language Production, Language Development/Acquisition