👤 Anja Soldan

Cognitive resilience, the ability to maintain better than expected cognitive function despite neuropathological burden, is a key contributor to clinical outcomes in Alzheimer's disease (AD), though the underlying neurobiological mechanisms remain poorly understood. To determine whether hippocampal volume and microstructure moderate the relationship between early tau pathology and cognitive performance, thereby serving as potential markers of cognitive resilience. Cross-sectional observational study. Participant data was obtained from the longitudinal BIOCARD Study, a volunteer-based research cohort. The sample included 190 dementia-free adults (mean age = 68 years), comprising 176 cognitively unimpaired individuals and 14 with mild cognitive impairment (MCI). Hippocampal volume and microstructure (mean diffusivity (MD)) were measured using structural magnetic resonance imaging (MRI) and diffusion-weighted imaging (DWI), respectively. Tau pathology was measured using FMK-6240 tau PET imaging across Braak stages I-III. Cognitive performance was indexed using global and domain-specific composite scores. Regression models tested the interactions between hippocampal volume or MD and tau burden, adjusting for demographics, APOE genotype, amyloid status, and diagnostic status. Lower hippocampal MD (indicative of better microstructural integrity) attenuated the negative association between tau burden in Braak stages II-III and both global cognition and episodic memory (ps < 0.010). Logistic regression models indicated that lower hippocampal MD was associated with a weaker relationship between tau burden in Braak stages II-III and the likelihood of MCI diagnosis (ps < 0.050). In contrast, hippocampal volume did not moderate the relationship between tau and any cognitive outcome (ps > 0.250). Hippocampal MD may serve as a promising imaging marker of cognitive resilience to early tau pathology, with potential utility for risk stratification and as a target for preventive interventions in AD. Show less

Prior studies have demonstrated the existence of cognitively-defined subgroups among dementia free older adults, however, it is unclear whether such subgroups are characterized by distinct neuroimaging measures of brain function and structure. To address this gap, the current study used latent profile analysis (LPA) to identify cognitively-defined subgroups in a sample of 167 (mean age = 69 years) dementia-free older adults with cognitive testing, amyloid PET, and multimodal brain MRI scans. The cognitive test scores covered the domains of episodic memory, executive function, language, and visuospatial processing. Linear regression models tested the associations between subgroup membership and neuroimaging measures, adjusting for age, sex, and years of education. Based on the LPA, three cognitive subgroups were identified: (1) high-average cognition (n = 61, 36%), (2) average cognition (n = 88, 53%), and low-average cognition (n = 18, 11%). Compared to the high-average group, the low-average group had lower volumes in cortical regions sensitive to Alzheimer's disease, lower global white matter microstructural integrity measured by diffusion tensor imaging, and higher global white matter hyperintensity burden. There were no group differences in global PET amyloid burden. Additionally, the high-average group tended to have higher resting-state functional connectivity within large-scale cognitive networks than the other two groups. These results suggest that cognitively-defined subgroups among older adults without dementia are associated with several measures of brain structure and function. Evaluating brain structure/function differences among dementia-free older adults may help identify individuals at greatest risk for future cognitive decline. Show less