This article is from the Monthly Science et Avenir – La Recherche n°900, dated February 2022.

A ray of light or sunshine and the inevitable burst of sneezes follow. A syndrome is far from being rare as it affects one in four people. Its scientific name: the photo-sneeze reflex or heliotropic sneeze, or “achhu”, is a humorous acronym for the autosomal dominant hypnotic helio-ophthalmic outburst. Although described since Aristotle, this particular type of sneezing is poorly understood.

Comments from the 1950s

The first scientific observations date back to the 1950s, when a French researcher, Jean Sedan, reported sneezing in some patients exposed to light from their eyeballs during a retinal exam. But recently, in October 2020, the first large-scale survey on the subject was launched in the United Kingdom, the Oxford Photonic Sneeze Survey. Still in progress, it is coordinated today by a psychologist in Munich (Germany), Manuel Spitschen, from Oxford (United Kingdom). This expert in chronology also suffers from achu himself. ,This reflex fascinates me, The researcher explains. Since the research so far has not satisfactorily explained the mechanism behind this, I wanted to know more.,

But before exploring the role of light, we must remember what internally sneezing is. In fact, it is a completely natural reflex like coughing. The phenomenon, which lasts only a few seconds, responds to a tickle in the nose, which is often caused by various attackers (dust, irritants, pollen, viral particles, etc.). At the level of the nasal mucosa, near the eyelids of sensory cells, are the nerve endings of a nerve, the trigeminal, which plays a very important role in the sensory and sensory transmission of many information on the facial scale. In the case of nasal irritation, it is it that sends signals to the brain that trigger the sneezing. This results in a progressive contraction of the respiratory muscles of the thorax, abdomen and pharynx. These block, the air pressure gradually rises from the chest to the top of the body and the back of the throat before the mouth opens and the final gulp of sputum is sometimes projected several meters away, if one moves one’s elbow or one’s handkerchief quickly. Sufficient.

This free reflex thus makes it possible to get rid of the invaders before they reach the lungs. It sometimes repeats itself, resulting in repeated sneezing that maximizes its effectiveness. Hence the importance of not suppressing it. Especially since avoiding sneezing can be dangerous (see box below). According to a publication that was published just ten years ago Facebook JournalSneezing will also have a second purpose: to revitalize the mucus circulatory system, the secretions of the nasal mucosa, whose role is to trap and eliminate dust.

never stop a sneeze

Spontaneous perforation of the pharynx and eight days in the hospital. Thus ended the journey of a 34-year-old Briton. After trying to suppress a sneeze, she immediately found herself in the emergency room, her neck swollen, red, and very painful. Story reported by doctors at University Hospital of Leicester (UK) in 2018 british medical journal Ended up with this simple recommendation: Never hold back. Other risks, according to the authors: perforation of the eardrum and even a ruptured brain aneurysm. France Alzheimer’s also warns of the long-term consequences of blocking termination. Hyperpressure applied to the vessels can cause repeated vascular microlesions, because of the many potential areas of brain fragility that are easy to avoid at once.

The coordinator of this work at the University of Pennsylvania (USA), Dr. Noam Cohen, used this image: “When a computer starts to slow down, we turn it off and then restart it, it works better. Sneezing is the equivalent of restarting for the respiratory system: it restarts the machine.“But how is light involved in this process? In the case of Aachu, neither dust grains nor viral particles activate the famous sneezing machine. It is only a simple light, natural or artificial. In this disorder There is probably a genetic component, but it remains mysterious. Because few teams have been interested in it. The question has been the subject of barely a hundred scientific publications. The explanation may be physiological and depend on the proximity of the nerve endings to the trigeminal nerve. The optic nerve. Stimulated by light reaching the retina, the optic nerve will be activated first but its fibers will somehow short-circuit along the trigeminal. This will cause sneezing. In 2010, according to a work published in one moreResearchers from the University of Zurich (Switzerland) have put forward another hypothesis: that of the higher sensitivity of the visual cortex of concerned individuals with respect to the optic nerve.

The neurons involved have been identified

To date, no demonstration confirms these hypotheses. And except for the preventive wear of sunglasses, solutions to help “achuars” are practically non-existent, especially if they run the risk of being exposed to sudden changes in light intensity – such as walking out of a tunnel. When light suddenly follows darkness. There is also a study, not on road drivers, but on airplane pilots, that was published in the 1990s in the journal military medicine, which revealed the occurrence of the photic sneeze reflex under these conditions in susceptible subjects. The Oxford Photonic Sneeze Survey is therefore continuing to find out whether, with 300 volunteers recruited through the press or through social networks. Through questionnaires sent to them, they were able to accurately describe the circumstances of the sneezing: the exact time of day, their frequency, intensity, duration, any associated signs…

,Most report a delay of five to ten seconds between exposure to light and sneezing“Have already seen the manual spitschen, aimed at”better understand what triggers the photic sneeze reflex and try to identify the exact stimulus“. When they have published their first results, the researcher also plans to test different wavelengths of light with volunteers. While waiting to solve all of Aachu’s mysteries, other scientists directly identify the brain regions involved. Trying to. In sneezing. This is the case of the team from Washington University in St. Louis (Missouri, USA).

In June 2021, it took an important step forward in mice, in particular by managing to identify the groups of neurons involved, with very high precision. These pioneering works published in the journal room demonstrated, an additional achievement, that it was also quite possible to control rodents’ sneezing by blocking them. How? ‘ or ‘ what? In the supporting video, scientists exposed rodents to irritant molecules, such as capsaicin from peppers. They then identified the presence of a neurotransmitter, neuromedin B (NMB), in their nasal cavity, which is secreted by neurons located in the brain stem and equipped with receptors for this neurotransmitter. The scientists then realized that administering NMB was sufficient to make the rodents sneeze immediately. Conversely, by blocking the receptors, they even succeeded in inhibiting them! Still a very fundamental work which in any case shows that the research on sneezing is more than ever before,