Inhibitory control in a combined motor and perceptual inhibition task : a study in young and older adults

Interacting efficiently with our environment necessitates perceptual inhibition of irrelevant stimuli and subsequent motor inhibition of inappropriate responses; these processes decline with age; however, the extent to which they interact and share neural resources remains unknown. Young (n=22; <35 yrs) and older adults (n=26: >60 yrs) completed a Flanker Task (perceptual inhibition), a Stop-Signal Task (SST; motor inhibition) and a combined task involving both Flanker and SST. Frontal Near-Infrared Spectroscopy (fNIRS) was used to assess Pre-frontal Cortex (PFC) activity, while electromyography (EMG) recorded muscle responses. Based on extant literature, it was hypothesised that age-related deficits in inhibitory processes would be observed for the SST but not for the Flanker Task and that these age-related deficits would be accentuated in the combined task. We observed age-related slowing (but not specific perceptual decline) in the Flanker task and age-related inhibitory decline in the SSTs; both groups’ performance declined to a similar degree when combining tasks. Only older adults exhibited significantly greater PFC activation in incongruent v. congruent trials (in Flanker and Combined tasks), suggesting a compensatory mechanism to reduce ageing-related decline. Older adults also responded with less vigour, indicating proactive changes in the voluntary response, conceivably to facilitate subsequent response inhibition.