Cognitive Control in the adult life-span

A number of cognitive deficits are associated with aging, including an increased distraction produced by non-target information in the environment. The cognitive and neural mechanisms underlying this deficit are still unclear. Recent event-related potential (ERP) studies show age-related differences in the ability to suppress the processing of non-target stimuli and the preparation of a response to them. A first study showed an age-related increase in the precentral nogo-P3 component to non-target stimuli which are supposedly easy to discriminate from target information since they belong to a different semantic domain (numbers vs. letters). This finding was replicated in a subsequent study, in which go and nogo stimuli were matched for frequency and conflict level in order to minimize the impact of task difficulty, probability monitoring, or conflict detection and resolution on the age-related ERP differences. The amplitude of the central nogo-P3 negatively correlated with go-RTs, suggesting that a partial response preparation to nogo events is strongly suppressed in older adults (as marked with nogo-P3), especially faster ones. In a third study, despite matched performance in two age groups, older adults showed an early sub-threshold response preparation, as marked with the Lateralized Readiness Potential (LRP), for both high- and low-conflict nogo stimuli. These results indicate that, even without age-related performance differences, older individuals show enhanced response preparation to non-target stimuli that can be detected with more sensitive measures such as the LRP. Negative correlations between nogo-LRPs and P3 on one side, and go-RTs on the other, in the older group only, suggest that inappropriate response preparation (LRP) and subsequent suppression (P3) for nogo stimuli is the cost to pay to maintain optimal response speed to targets in normal aging. Corroborating this account, the amplitude of the LRP to low-conflict nogo stimuli was also positively correlated with that of the following nogo-P3. Do age-related differences in suppressing non-target material impact subsequent performance? To assess this issue, younger and older adults first performed a go/nogo task with coloured letters used as conflicting go/nogo stimuli, and two coloured numbers as low-conflict nogo stimuli. Then, they performed another go/nogo task. A previous number was re-used as a nogo stimulus and the other number as a go stimulus, with new numbers serving as go/nogo baselines. In a first block, younger adults showed transfer costs, that is, slower responses to previous-nogo/now-go numbers than new go numbers, an effect not shown by older adults. These results suggest a tonic suppression of non-target information in younger adults, which gives rise to transfer costs, when this information becomes relevant, while older adults are unable to keep tonic inhibition. In conclusion, the present data show that, to compensate for general slowing, older adults start processing every environmental stimulus, independently of its target/non-target status, and then reactively suppress pre-activated responses to non-target stimuli. Possible underlying mechanisms include a difficulty in maintaining a task-set, for instance by means of a proactive and tonic suppression of inappropriate processing of non-target information.