Despite its seemingly neutral function, unconscious sighing is actually an important, life-sustaining reflex that is designed to preserve lung function, according to a new study released by researchers from the University of California, Los Angeles. In the study, the team locates two tiny clusters of neurons in the brain stem whose function is to convert normal breathes into sighs. The findings could help scientists come up with treatments for patients that cannot breathe deeply on their own.
"Sighing appears to be regulated by the fewest number of neurons we have seen linked to a fundamental human behavior," Jack Feldman, who participated in the research, said in a press release. "One of the holy grails in neuroscience is figuring out how the brain controls behavior. Our finding gives us insights into mechanisms that may underlie much more complex behaviors."
Mark Krasnow, a professor of biochemistry at the Stanford University School of Medicine who also participated in the research, believes that the new findings have uncovered an important part network of brain stem cells for the generation of breathing rhythms.
"Unlike a pacemaker that regulates only how fast we breathe, the brain's breathing center also controls the type of breath we take," Krasnow said. "It's made up of small numbers of different kinds of neurons. Each functions like a button that turns on a different type of breath. One button programs regular breaths, another sighs, and the others could be for yawns, sniffs, coughs and maybe even laughs and cries."
Krasnow and his Stanford team examined over 19,000 gene-expression patterns in animal brain cells and found approximately 200 neurons in the brain stem that create and release two neuropeptides that enable brain cell communication, although they were unsure of which cells they were communicating with and why.
On the other hand, Feldman and his team already knew that the same family of peptides, which are also found in humans, played an active role in the part of the brain that influences breathing and sighing, although they were unaware of the genes that controlled them. By combining their efforts with Krasnow's team, the labs discovered that the peptides stimulated an additional set of 200 neurons that activate mouse breathing muscles to produce a sigh at a rate of roughly 40 times per hour.
"These molecular pathways are critical regulators of sighing, and define the core of a sigh-control circuit," Krasnow said. "It may now be possible to find drugs that target these pathways to control sighing."
The findings were published in the Feb. 8 issue of Nature.
