Structural MRI predictors of cognition and incident dementia differ across african americans, hispanics, and whites

Structural magnetic resonance imaging (MRI) provides key biomarkers to predict onset and track progression of Alzheimer's disease (AD). However, most published reports include racially, ethnically, and socioeconomically homogenous samples. Racial/ethnic differences in MRI variables and cognitive performance, as well as health, socioeconomic status and psychological factors, raise the possibility that brain-behavior relationships may be stronger or weaker in different groups. The current study tested whether MRI predictors of cognition and incident dementia differ in African Americans and Hispanics, compared with non-Hispanic Whites. Participants were 638 initially non-demented older adults (29% non-Hispanic White, 36% African American, 35% Hispanic) in the Washington Heights-Inwood Columbia Aging Project. Hippocampal volume, regional cortical thickness, infarcts, and white matter hyperintensity (WMH) volumes were quantified with FreeSurfer and in-house developed procedures. Composite scores of memory, language, speed/executive functioning, and visuospatial function were derived from a neuropsychological battery administered at the time of the MRI. Dementia diagnoses were made via consensus conference every two years for up to 10 years. Multiple-group regression or survival analyses tested whether associations between MRI variables and (1) concomitant cognitive performance or (2) incident dementia differed across groups. In cross-sectional analyses, larger WMH volume was associated with worse language and speed/executive functioning among African Americans, but not among non-Hispanic Whites. Larger hippocampal volume was more strongly associated with better memory among non-Hispanic Whites compared with Hispanics. We have previously shown that larger WMH volume and smaller hippocampal volume predict incident dementia in this sample. Current longitudinal analyses show that the association between hippocampal volume and dementia incidence differs across race. Specifically, smaller hippocampal volume was associated with incident dementia among non-Hispanic Whites, but not among African Americans. Among African Americans, only larger WMH volume predicted incident dementia. MRI predictors of incident dementia did not differ between Hispanics and non-Hispanic Whites. Structural MRI predictors of concomitant cognition and 10-year dementia incidence differed across racial/ethnic groups. These results highlight the critical need for more diverse samples in the study of cognitive aging and AD, as the neurobiological substrates of cognitive and functional impairment may be different for different groups.