Superficial white matter and gray matter jointly support cognition among older adults in India

INTRODUCTION: The relationships between superficial white matter (SWM) and cognition, and its interaction with gray matter (GM), remain unclear in community-based populations. METHODS: We analyzed data from 459 older adults in the Harmonized Diagnostic Assessment of Dementia for the Longitudinal Aging Study in India. SWM microstructures were estimated by multi-shell diffusion magnetic resonance imaging (MRI). We examined cross-sectional associations between SWM with memory, language, executive, visuospatial function, and cognitive impairment (CI); and tested SWM interactions with GM atrophy and modification by socioeconomic status. RESULTS: Higher SWM neurite density index (NDI) related to better language, whereas higher fraction of isotropic water (FISO) related to greater odds of CI. While GM metrics remained strongest predictors of cognition, these associations were attenuated by better SWM integrity (high NDI and low FISO). No formal education, low literacy, and rural residence worsened SWM-related language deficits. DISCUSSION: Neurite-level SWM health may drive resistance to neurodegeneration and cognitive decline.