Noradrenergic responsiveness supports selective attention across the adult lifespan

Abstract

Selectively attending to relevant information while blocking out distractors is crucial for goal-directed behavior, yet with advancing age, deficits emerge in attentional selectivity. Decrements in attention have been associated with altered noradrenergic activity in animals. However, research linking noradrenergic functioning to attention in aging humans is scarce, likely reflecting long-standing methodological challenges in noninvasive assessments. We studied whether age-related differences in the noradrenergic system predict differences in attention. We measured pupil dilation, a non-invasive marker of arousal-related norepinephrine (NE) release, while concurrently recording the electroencephalogram (EEG), of male younger (N=39; 25.2±3.2 years) and older adults (N=38; 70.6±2.7 years). Arousal was modulated on a trial-by-trial basis using fear-conditioned (CS+) stimuli. During conditioning, pupil and EEG markers related to heightened arousal were identified. Afterwards, in a dichotic listening task, participants were cued to direct attention to either the left or right ear while highly similar syllable pairs were presented simultaneously to both ears. During the dichotic listening task, presentation of fear-conditioned stimuli reinstated the acquired arousal response, as reflected in pupil and EEG alpha-beta-band responses. Critically, pupil dilation to CS+ was correlated with stronger EEG alpha-beta desynchronization, suggesting a common dependence on NE release. On a behavioral level, stronger arousal reactions were associated with better attention. In particular, structural equation modeling revealed that the responsiveness of the NE system is associated with attention on a latent construct level, measured by several indicator tasks. Overall, our results suggest that the responsiveness of the NE system supports attention across the lifespan.