Facing healthy and pathological aging: A systematic review of fMRI task-based studies to understand the neural mechanisms of cognitive reserve.

Cognitive reserve (CR) explains the varying trajectories of cognitive decline in healthy and pathological ageing. CR is often operationalized in terms of socio-behavioural proxies that modulate cognitive performance. Individuals with higher CR are known to maintain better cognitive functions, but evidence on the underlying brain activity remains scattered. Here we review CR studies using functional MRI in young, healthy and pathologically elderly individuals. We focus on the two potential neural mechanisms of CR, neural reserve (efficiency of brain networks) and neural compensation (recruitment of additional brain regions), and the effect of different proxies on them. The results suggest increased task-related activity in different cognitive domains with age and compensation in case of difficult task and pathology. The effects of proxies lead to increased neural reserve (reduced brain activity) in both older and younger individuals. Their relationship with compensation remains unclear, largely due to the lack of young adult samples, particularly in clinical studies. These findings underscore the critical role of lifelong engagement in mentally enriching activities for preserving cognitive function during aging. New studies are encouraged to refine the CR theoretical and empirical framework, particularly regarding the measurement of socio-behavioral proxies and their relationship with cognitive decline and neural underpinning.