In an effort to decode the complex taste sensation of soda, researchers have uncovered evidence that fizzy drinks set off the very same nasal sensors as mustard and horseradish.
The nasal nerves in question are triggered in reaction to feelings of pain, skin pressure and temperature changes in the nose and mouth, the researchers reported.
The findings establish that carbonated drinks provoke a spicy, burning sensation, a finding that builds on U.S. National Institutes of Health and University of California, San Diego 2009 research that revealed that sodas also activate tongue cells that convey a feeling of sourness.
"Carbonation evokes two distinct sensations," senior study author Emily Liman, an associate professor of neurobiology in the University of Southern California's College of Letters, Arts and Sciences, explained in a university news release. "It makes things sour and it also makes them burn."
"We have all felt that noxious tingling sensation when soda goes down your throat too fast," Liman added. "What we did not know was which cells and which molecules within those cells are responsible for the painful sensation we experience when we drink a carbonated soda."
But as Liman and her colleagues report in the Sept. 29 issue of the Journal of Neuroscience, the mystery has been solved.
The authors worked in a lab setting where they poured carbonated saline over a dish of nerve cells drawn from the sensory nerves of the nose and mouth.
The result: The one type of cell that activated was the same pain sensor that activates in response to mustard.
What's more, a particular gene expressed by this cell -- the TRPA1 gene -- was pinpointed as the switch turned on by the carbon dioxide found in sodas.
In response to those who wonder why people would indulge in a beverage linked to pain circuits, Liman speculated, "it may be a macho thing."