The influence of age-related cognitive decline on action, cognitive and perceptual inhibition : a systematic review and meta-analysis

Efforts to improve the current understanding of pre-clinical dementia largely focus on memory function. While non-memory executive functioning, including inhibitory control, is known to be impaired in dementia, it is unclear how different types of inhibitory behaviours are affected in the early pre-clinical dementia stage. Mild cognitive impairment (MCI), particularly with memory impairments (amnestic MCI or aMCI), puts people at a higher risk for dementia. This systematic review and meta-analysis investigates the extent to which performance in different inhibitory tasks varies in individuals diagnosed with MCI, aMCI or Alzheimer’s disease (AD) compared to controls. Ensuring PRISMA-selection criteria, the findings of 45 papers including individuals with AD (n = 1097), MCI (n = 582), aMCI (n = 741) and controls (n = 2639) revealed strong and small-to-moderate effects of AD on performance in the Simon (g = 1.626) and Stroop tasks (g = 0.461) respectively, and a strong and small effect of MCI on performance in the Flanker (g = 0.855) and Go/No-Go tasks (g = 0.341) respectively. The aMCI groups showed no significant difference in inhibitory control compared with controls across all tasks. Overall, rather than supporting a generalised inhibitory control deficit in MCI or AD, the current results indicate that different inhibitory tests are sensitive to performance changes at different stages of cognitive decline. Conceivably, specific inhibitory tasks (such as Simon or Stroop) may assist in the early detection of AD. Despite the limited number of studies in all but the Stroop task, there is evidence that impaired inhibitory function can be detected in AD, but it may not present in prodromal aMCI stages highlighting the importance of further longitudinal studies to more accurately understand the non-linear time course of inhibitory performance with advancing cognitive decline.