The effect of beta-amyloid on face processing in young and old adults: A multivariate analysis of the BOLD signal

The recent ability to measure in vivo beta-amyloid (Aβ), a marker of Alzheimer's disease (AD), has led to an increased focus on the significance of Aβ deposition in clinically normal adults. Evidence suggests that healthy adults with elevated cortical Aβ show differences in neural activity associated with memory encoding-specifically encoding of face stimuli. Here, we examined if Aβ deposition in clinically normal adults was related to differences in neural activity in ventral visual cortex during face viewing. Our sample included 23 high-Aβ older adults, 23 demographically matched low-Aβ older adults, and 16 young adults. Participants underwent cognitive testing, Aβ positron emission tomography imaging with ¹⁸F-Florbetapir, and functional magnetic resonance imaging to measure neural activity while participants passively viewed photographs of faces. Using barycentric discriminant analysis-a between-groups classification technique-we found that patterns of neural activity in the left fusiform gyrus, a region highly responsive to faces, distinguished Aβ status of participants. Older adults with elevated Aβ were characterized by decreased activity in left fusiform compared to Aβ-negative older adults. Further, we found that the degree to which older adults expressed decreased fusiform activity was related to worse performance on tasks of processing speed. Our results provide unique evidence that, in addition to previously studied memory and default regions, decreased neural activity in a region important for face perception was associated with elevated Aβ and may be an early manifestation of AD.