Pupil-based arousal self-regulation: impact on physiological and affective responses to emotional stimuli

Pupil-based biofeedback has been shown to enable healthy participants to volitionally control locus coeruleus-mediated arousal. The locus coeruleus is considered a critical player in the central stress circuitry and dysfunctions in the system, causing dysregulated arousal levels, have been tightly linked to neuropsychiatric disorders such as anxiety and stress-related disorders and stress-induced cardiovascular vulnerability. Yet, it remains unclear whether physiological and self-rated affective responses to emotional stimuli are influenced by volitional control of arousal levels. In this study, healthy participants were presented with emotional (negative) or neutral sounds while they self-regulated (i.e., up- and downregulated) pupil size and pupil-linked arousal levels, a skill acquired through prior pupil-based biofeedback training. While no immediate online effect of such self-regulation on self-rated affect experience was observed, greater gains in pupil downregulation training predicted reduced affect experiences, particularly in response to negative sounds. Furthermore, larger pupil dilation responses to sounds were found during both pupil size up- and downregulation compared to a non-regulatory control condition, potentially indicating regulatory effort associated with pupil self-regulation. However, heart rate responses significantly decelerated during sound presentation and concurrent pupil size downregulation, suggesting parasympathetic dominance. These results provide the first evidence that pupil-based biofeedback training may modulate both self-rated and physiological responses to emotional sounds to a certain extent, highlighting its potential as a tool for reducing hyperarousal and hyperresponsivity to emotional sounds, as seen in anxiety and stress-related disorders, through pupil-linked arousal self-regulation.