Impaired Sensory-motor Reconfiguration and Pupil-linked Arousal in Aging

Mounting evidence points to a key role of the brainstem arousal systems in controlling the adaptation of behavior to changing contexts. Both, brainstem arousal systems and cognitive flexibility seem to deteriorate in aging. We hypothesized that these two impairments are related. To test this hypothesis in humans, we compared adaptive behavior and arousal dynamics between older and younger adults (60% women). Arousal dynamics were measured by means of luminance-independent pupil responses. Participants performed a hierarchical decision-making task, which required frequent switches between two stimulus-response mapping rules for reporting a perceptual categorization judgment. These rule switches were hidden, and participants needed to infer them from noisy evidence. Older adults were less accurate than younger adults. This impairment was due to more frequent use of the incorrect rule. Neither the perceptual categorization nor the detection of rule switches differed between age groups. Moments of high probability of rule switches were associated with pupil dilation in both age groups, which was, however, reduced in older people. We propose that impaired cognitive recruitment of pupil-linked arousal in aging might limit the ongoing reconfiguration of the neural pathways that support flexible cognitive behavior.