Age-related modulations of alpha and gamma brain activities underlying anticipation and distraction

Attention operates through top-down (TD) and bottom-up (BU) mechanisms. Recently, it has been suggested that these mechanisms are supported by distinct frequency bands with slower (alpha) frequencies indexing facilitatory and suppressive mechanisms of TD attention and faster (gamma) frequencies indexing BU attentional capture. Ageing is characterized by increased behavioral distractibility, which can result from either a reduced efficiency of TD attention, or an enhanced triggering of BU attention. However, only few studies have investigated the impact of ageing on the balance between TD and BU attention and its oscillatory correlates. MEG data were collected from 14 elderly (mean age = 67) and 14 matched young (mean age = 25) healthy human participants while performing a modified version of the Competitive Attention Task with pitch discrimination. TD attention was manipulated by a visual cue that was either informative or not of the side of the monaural target sound. BU attention was triggered by binaural distracting sounds that were played (25% of trials) between the cue and the target. Behaviorally, older participants displayed an exacerbated distractibility to late distractors. Electrophysiologically, in comparison to young participants, they exhibited (1) deficits in the suppressive mechanisms of TD attention, indexed by a reduced alpha synchronization in task-irrelevant visual regions, (2) less prominent alpha peak-frequency differences between cortical regions, (3) a similar BU system activation indexed by distractor-induced gamma responses, and (4) a reduced activation of prefrontal inhibitory control regions. These results show that the ageing-related increased distractibility is of TD origin.