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Sneezing Induced by Bright Light Is Subject of Study

In research published in PLoS ONE, scientists from the University of Zurich examined the curious and apparently highly prevalent phenomenon called the “photo-induced sneeze reflex” or “sun sneeze.” This reflex is characterized by the induction of a sneeze upon sudden exposure of a dark-adapted subject to intensive bright light and, according to one previous study, is seen in almost 25% of normal individuals. Although generally considered harmless, it has been hypothesized that photic sneezing is, at least in part, a causal factor in conduction deafness, mediastinorrhexis, and cerebral hemorrhage. Previous studies have pointed out that photic sneezing could be dangerous for individuals in certain professions, such as baseball outfielders, high-wire acrobats, and airplane pilots, or in commonly experienced situations such as driving out of a tunnel, which can triple the risk of sneezing. The Zurich researchers said that their results demonstrated that photic sneezers have a generally enhanced excitability of the visual cortex to standard visual stimuli, and that a stronger prickle sensation in the nose of photic sneezers was associated with both activation in the insular cortex and stronger activation in the secondary somatosensory cortex. Thus, while the results of this study do not contradict those theories that emphasize the role of reflex pathway in the brain stem of photic sneezers, they do, the researchers said, support the view that even cortical circuits, rather than just brainstem circuits, might play a pivotal role in controlling (or modulating) this extraordinary and rarely investigated behavior. The researchers said that the photic sneeze reflex is therefore not a classical reflex that occurs only at a brainstem or spinal cord level, but, in stark contrast to many theories, also involves specific cortical areas. The article was published online on February 15, 2010. [PLoS ONE article]