Age-related Inhibitory Decline: Examining Inhibition Sub-Components and their Impact on Sustained Attention in Healthy Ageing

The inhibition deficit hypothesis postulates that inhibitory functioning declines with age, which negatively impacts other cognitive abilities. Yet still, the influence of healthy ageing on inhibitory functioning remains unclear, with the multifaceted nature of inhibition often an overlooked factor. Moreover, no prior study has empirically tested whether inhibition explains differential age-effects in sustained attention. Thus, we cross-sectionally investigated the inhibition deficit hypothesis in eighty healthy older adults (mean age = 67.78 years, 44f) administering three inhibition tasks (i.e., flanker, Stroop, and go/no-go), each measuring a distinct sub-component process, and one sustained attention task (i.e., SART) via the PsyToolkit platform. No significant bivariate relationships were identified among the inhibition measures. Semi-partial correlations (rho) of the three inhibition sub-component measures (correcting for gender and education) with age resulted in significant positive relationships with task performance on the Stroop and go/no-go, such that older individuals had more pronounced Stroop effects and worse go/no-go accuracy, respectively. Lastly, go/no-go performance completely mediated the relationship between ageing and sustained attention performance, whilst Stroop effects partially mediated this association. The lack of significant inter-task correlations supports the independence of these sub-component processes of inhibition and cautions against conflating these sub-components into a generalised concept of inhibition. Further, age-related declines were observed in specific inhibition tasks, which speaks against a general inhibition deficit in healthy ageing. The mediation findings demonstrate that inhibitory sub-components account for age-related declines in sustained attention, over and beyond ageing itself via an indirect path, representing an important cognitive domain to maintain throughout ageing.