Background and Objectives: Based on mixed findings from previous research, researchers have hypothesized autism may be a protective or risk factor for age-related cognitive decline/dementia, or that autism does not influence it (parallel aging). To differentiate between hypotheses, longitudinal studies that account for autism underdiagnosis, are needed and lacking. This study examined if higher autistic traits in adults aged 50+ are associated with a greater risk of spatial working memory (SWM) decline, a key cognitive domain affected in both healthy aging and autism. Research Design and Methods: Participants from the online PROTECT cohort (n = 13,390) were classified into 3 groups based on autism spectrum traits (AST): high (H-AST, n = 205), intermediate (I-AST, n = 589), and no traits (COA, n = 12,451). Spatial working memory performance was captured annually across 7 years. Growth mixture models (GMM) and latent growth curve models were estimated to examine the relationship between AST and SWM. Results: Growth mixture models revealed an optimal 1-class quadratic solution, consistent across groups. There were no significant differences between AST groups in baseline SWM (p = .837). Autism spectrum traits were not associated with SWM at baseline (B = 0.01, SE = 0.05, p = .901) or SWM trajectory (B = 0.00, SE = 0.01, p = .856), regardless of accounting for covariates. Discussion and Implications: Findings suggest a single SWM trajectory in middle-aged/older adults with higher autistic traits and no autistic traits. Future research should address if these broader autism phenotype results are replicated in diagnosed autism groups.</p
