Relationships between AD‐related neuroanatomy and cognitive, physical, and social aging in vervet monkeys

Abstract

AbstractBackgroundIn humans, social integration wanes with age, a pattern hypothesized to stem from cognitive or physical decrements. Social isolation increases dementia risk. Nonhuman primates provide important translational opportunities to study brain‐body relationships that may promote healthy or pathological aging. Vervet monkeys (Chlorocebus sabaeus), like humans, have complex central nervous systems and naturally experience cognitive, functional, and neuroanatomical changes with age. These changes often recapitulate characteristics of early Alzheimer’s disease (AD), including Aβ accumulation in the brain, reduced CSF Aβ, and greater Aβ plaque burdens accompanied by reduced brain volumes.MethodWe studied 25 females, aged 8‐29 years (middle to very old‐aged), living in long term, stable, social groups. Using a cross‐sectional study design, we tested whether cognitive (executive function and working memory) or physical (gait speed) function mediated the effects of age on social behavior. We also used T1‐weighted structural MRI to test whether the cortical thickness of an AD‐signature region of interest (“meta‐ROI”) predicted social participation at one year follow‐up.ResultCognitive (executive function: b = ‐0.603; p = 0.038; working memory: b = ‐0.537; p<0.001) and physical (gait speed: (b = ‐1.005; p = 0.043) function were negatively associated with age. Time spent in affiliative behavior was inversely related to age (b = ‐0.723; p = 0.009), whereas time spent alone was higher for older‐aged monkeys (b = 0.723; p = 0.009). Time spent grooming others decreased with age (b = ‐0.217; p<0.001), but time receiving grooming did not (b = ‐0.057; p = 0.333). The number of social partners groomed diminished in aged subjects (b = ‐0.145; p<0.001). The relationships between age and sociality were mediated, in part, by cognitive function: higher degrees of executive function had a positive mediating effect on time spent in grooming interactions (b = 0.120; p = 0.047). Conversely, social participation was not mediated by physical performance. Finally, thinner cortices in the meta‐ROI predicted greater social isolation (t = ‐2.199; p = 0.038) and fewer numbers of social partners (z = ‐2.319; p = 0.020) at one year follow‐up.ConclusionThese results suggest that: 1) cognitive, physical, and social function of vervets decline with age like humans; 2) aging vervets are not socially excluded but decreasingly engage in social behavior; and 3) cognitive deficits stemming from cortical gray matter deficits may underlie the relationship between aging and social decline.