GFAP and Alzheimer disease: METHODS: In a 1-year longitudinal cohort of 71 cognitively unimpaired adults, we assessed baseline VR-PI performance (PI error and angular error), AD-related plasma biomarkers (p-tau181 and glial fibrillary acidic protein [GFAP]), and longitudinal cortical thickness and volume from MRI scans acquired one year apart, to examine whether baseline PI performance was associated with both plasma biomarkers and subsequent structural brain changes.