A groundbreaking study by the Karolinska Institutet in Sweden has uncovered a new factor that influences the dilation of the pupil: our breath. Published in The Journal of Physiology, the report reveals an intimate link between our respiratory patterns and pupil size, with the pupil contracting during inhalation and dilating during exhalation. This cyclical phenomenon could potentially impact our vision, akin to the aperture of a camera regulating light exposure.
The pupil’s pivotal role in controlling the light that reaches our retina is well-known. It plays a key part in our visual perception, adjusting to variations in lighting, focusing distance, and cognitive stimuli such as emotions or mental exertion. The recent discovery adds a fourth element to this list, revealing that our respiration can also modulate pupil size, independent of any external stimuli.
Artin Arshamian, Associate Professor at the Department of Clinical Neuroscience, Karolinska Institutet, who spearheaded the study, elucidated on this unique mechanism. He noted that as breathing influences brain activity and cognitive functions, understanding this connection could enhance our grasp of how our vision and attention are regulated.
To validate this link, the researchers conducted a series of five experiments involving more than 200 participants, assessing how various breathing patterns and conditions impacted pupil size. The results were consistent across different breathing rates, nasal or oral breathing, varying lighting conditions and fixation distances, and whether participants were at rest or engaged in visual tasks. The difference in pupil size between inhalation and exhalation was significant enough to potentially affect vision.
Interestingly, the study found that this function was unaffected in individuals born without an olfactory bulb, a brain structure stimulated by nasal breathing. This implies that the brainstem, a fundamental component of the brain conserved through evolution, may control this mechanism.
The research team is now probing whether alterations in pupil size during respiration can indeed affect vision. Prior studies have indicated that smaller pupils aid in spotting minute details, while larger pupils facilitate the detection of elusive objects. Martin Schaefer, a Postdoctoral Researcher at the same department at Karolinska Institutet, and the study’s first author, posits that our vision could oscillate between distinguishing fine details during inhalation and identifying faint objects during exhalation within a single breath cycle.
The findings could also have implications in diagnosing and treating neurological disorders like Parkinson’s disease, where early symptoms often include impaired pupil function. Artin Arshamian expressed intent to delve into this area in future research. The Swedish Research Council and the European Research Council (ERC) funded this pioneering study.
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