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| Poster #155 The Pupillary Respiratory-Phase Response: Pupil size is smallest around inhalation onset and largest during exhalation |
| Martin Schaefer1, Sebastiaan Mathôt2, Mikael Lundqvist1,3, Johan N. Lundström1,4,5, Artin Arshamian1 1Karolinska Institutet, Stockholm, --, Sweden 2University of Groningen, Groningen, --, Netherlands 3Massachusetts Institute of Technology, Cambridge, MA, United States 4Monell Chemical Senses Center, Philadeplhia, PA, United States 5Karolinska University Hospital, Stockholm, --, Sweden |
Respiration profoundly influences brain activity, coordinating sensory processing and motor actions. However, its effect on pupil size, a critical indicator of visual perception and neural state, remains underexplored. In five experiments using a pre-registered protocol—we systematically investigated how respiratory phase affects pupil size across different conditions. In Experiment 1 (n = 50), we examined nasal and oral breathing at rest under dim lighting with nearby fixation points and discovered that pupil size fluctuates with the respiratory cycle, being smallest around inhalation onset and largest during exhalation. These results were replicated in Experiment 2 (n = 53) using an independent sample under identical conditions. Experiment 3 (n = 112) demonstrated that this pattern persists during active visual tasks, while Experiment 4 (n = 57) showed it remains robust under controlled breathing at varying paces under ambient lighting and distant fixation. Finally, in Experiment 5 (n = 34) individuals with isolated congenital anosmia (born without olfactory bulbs) were used as a lesion-type model during visual-auditory tasks to assess whether the respiratory-pupil link depends on olfactory bulb-driven oscillations. The results were consistent across all conditions and groups, indicating that the Pupillary Respiratory-Phase (PRP) response is independent of breathing route, task, or olfactory bulb function. We propose that the PRP response is governed by brainstem circuits, involving the preBötzinger complex and locus coeruleus, which modulate pupil size in synchrony with respiratory rhythms. This novel mechanism complements the three established drivers of pupil size—light, near fixation, and psychosensory responses—by introducing a cyclic modulation tied to the respiratory phase. |