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The Neural bases of orthographic word learning in older adults
Poster Session E, Sunday, September 14, 11:00 am - 12:30 pm, Field House
Robert W. Wiley1, Yuan Tao2, Sartaj Singh1, Brenda Rapp2; 1University of North Carolina Greensboro, 2Johns Hopkins University
Introduction: Tao et al. (2024) examined the neural bases of the initial stages of orthographic learning in neurotypical young adults learning spellings for novel pseudowords during fMRI scanning. There, we reported a distinctive bilateral hippocampal increase in BOLD response with the increasing memory strength of learning trials. In contrast, in ventral occipital temporal cortical (VOTC/VWFA) we observed the reverse pattern of decreasing BOLD response with increasing memory strength. These findings are consistent with Complementary Learning System theory (McClelland et al., 1995) that predicts complementary roles for subcortical and cortical learning mechanisms. Subsequently, Rapp et al. (2024) reported that older adults had significantly more difficulty than younger adults in learning new words spellings. Here, we follow-up on these studies to examine the neural bases of orthographic learning in older versus younger adults using the in-scanner orthographic learning paradigm from Tao et al. (2024). Methods: Participants were N = 18 younger (YA; ages 18-35) and N = 23 older (OA; ages 55-80) neurotypical adults. As in Tao et al. (2024), participants were tasked with learning the correct spelling of 10 novel pseudowords while undergoing two runs of fMRI scanning. There were eight trials for each target, and average accuracy across all trials was 74% for YA and 60% for OA. Trials were subsequently binned into “memory strengths” (MS; weak, medium, strong) as in Law et al. (2005). For each participant, mean BOLD response was extracted for each MS level bilaterally in the hippocampus and VWFA. Bayesian multilevel models were used to regress BOLD on MS, Group (OA vs YA), and their interaction, separately for the hippocampus and VWFA. Results: Behavior: In terms of in-scanner performance, the YA were significantly more accurate, M = 0.74, 95% CI [0.66, 0.82], compared to the OA, M = 0.60, 95% CI [0.54, .67]. The difference between groups was significant, t(39) = 2.65, p ≈ 0.01. Hippocampus: Across MS levels, the YA showed a significant rising BOLD response bilaterally (left: p < 0.01; right: p ≈ 0.02). The OA showed similar non-significant effects bilaterally (p’s > 0.21), although the pattern was not significantly different from the YA (p ≈ 0.21). VWFA: The YA showed a significant falling pattern across MS levels in both hemispheres (left: p < 0.01; right: p < 0.001). The OA showed non-significant effects in bilaterally (p’s > 0.34), and this pattern was significantly different from the YA (p ≈ 0.02). Conclusions We replicated the Tao et al (2024) findings that younger adults show distinct and complementary patterns of BOLD response in the hippocampus and VOTC during early orthographic learning. Furthermore, we show that older adults, who struggle to learn novel orthographic word forms, do not show these patterns. Instead, they exhibit an attenuated subcortical response in the hippocampus and a significantly different cortical response in the VOTC. These findings suggest that hippocampal weakness may trigger compensatory cortical responses.
Topic Areas: Writing and Spelling,