Phasic LC-NE firing and attentional profiles: a pupillometric study.

The locus coeruleus-norepinephrine (LC-NE) system plays a key role in regulating attention through phasic activation that enhances the processing of task-relevant stimuli. The present study assessed phasic activity by comparing pupil dilations across two attentional conditions: a high-demand discrimination task and a low-demand localization task, matched for visual input. The difference in response-locked peak pupil size between the two tasks served to isolate transient, task-evoked phasic related activity while minimizing baseline and perceptual confounds. To complement this paradigm with greater ecological validity, participants also completed the MOXO-d-CPT, a continuous performance task incorporating realistic visual and auditory distractors, yielding separate indices of attentiveness, impulsivity, hyperactivity, and timeliness. As expected, discrimination conditions elicited greater pupil dilation and showed increased attention demand. Exploratory correlation analysis revealed a significant association between response-locked phasic pupil responses and the MOXO attentiveness index, suggesting that individual differences in phasic LC-NE activity may relate to the ability to maintain performance under distraction. No significant associations were observed with the remaining MOXO indices; direct comparisons revealed that the attentiveness correlation differed significantly from the timeliness and hyperactivity correlations, but not from the impulsivity correlation; however, the present sample provides sufficient power only for detecting large effects. By combining two complementary paradigms, the study provides a more nuanced understanding of the functional role of phasic LC-NE activity. The findings offer initial evidence consistent with the involvement of phasic LC-NE activity in momentary attentional filtering rather than general attentional regulation, though research with larger samples is needed to establish generalizability.