Joint contributions from brain activity and activity-independent functional connectivity to working memory aging

Working memory (WM) impairment has been well characterized in normal ageing. Various studies have explored changes in either the regional activity or the interregional connectivity underlying the WM ageing process. We proposed that brain activity and connectivity would independently alter with ageing and affect WM performance. WM was assessed with a classical N-back task during functional magnetic resonance imaging in a community-based sample comprising 168 elderly subjects (aged 55 to 86 years old). Following the rationale of background functional connectivity, we assessed age-related alterations in brain activity and seed-based interregional connectivity independently. Analyses revealed age-related decrease in the activity of the inferior parietal lobule (IPL) and an increase in the activity of the ventral anterior cingulate cortex (ACC), and the local functional dysfunctions were accompanied by alterations in their connectivity to other cortical regions. Importantly, regional activity impairments in the IPL and ACC could mediate age-related effects on accuracy rate and reaction time, respectively, and those effects were further counterbalanced by enhancement of their background functional connectivity. We thus claimed that age-induced alterations in regional activity and interregional connectivity occurred independently and contributed to WM changes in ageing. Our findings presented the way brain activity and functional connectivity interact in the late adulthood, thus providing a new perspective for understanding WM and cognitive ageing.