Impact of cognitive load on pupil dilation: A comparative study of young and older adults.

Performance on the auditory working memory task declined with increasing digit sequence length across both younger and older adult groups.

• Participants performed immediate oral recall of digit sequences of varying lengths: 3, 6, or 9 digits.
• Performance decline occurred across both age groups as sequence length increased.
• Working memory performance was described as 'largely preserved in older adults' relative to younger participants.

Older adults exhibited significantly reduced pupillary reactivity compared to younger participants under higher cognitive load conditions.

• The difference in pupillary reactivity between age groups was significant specifically in the 6-digit and 9-digit conditions.
• No significant difference in pupillary reactivity between age groups was reported for the lower cognitive load (3-digit) condition.
• Pupil size was continuously recorded during task performance.
• The attenuation of pupillary response in older adults occurred despite relatively preserved behavioral performance.

Pupil dilation correlated with both age and Stroop interference scores.

• The correlation indicates an association between pupillary dynamics and executive (inhibition) control.
• Stroop interference scores were used as a measure of executive inhibition control.
• The correlation with age suggests pupillary reactivity changes systematically across the adult lifespan.

The locus coeruleus-noradrenergic (LC-NA) system is implicated as the neural substrate underlying the observed age-related differences in pupillary reactivity.

• Pupillary responses during cognitively demanding tasks are described as 'a non-invasive index of LC-NA system integrity.'
• LC-NA dysfunction has been implicated in age-related cognitive deterioration.
• Attenuated pupillary responses in older adults were interpreted as reflecting 'early functional alterations in the LC-NA system.'
• The LC-NA network plays a crucial role in sustaining cognitive function according to the authors.

Pupillary reactivity is proposed as a promising non-invasive biomarker of cognitive control and age-related neural integrity.

• The measure is described as non-invasive and continuously recordable during task performance.
• Pupillary responses reflect both cognitive effort and resource allocation.
• The biomarker potential is relevant in the context of age-related cognitive decline and risk of neurodegenerative disorders.
• The dissociation between preserved behavioral performance and reduced pupillary reactivity in older adults supports its sensitivity as an early marker.