The life-saving cause of sighing uncovered by scientists

It's not simply a sign of stress

(Jack Feldman/iStock)

Scientists have found what causes us to sigh, in findings which go against the common myth that it is simply a sign of despair.

The average person sighs every five minutes, amounting to 12 sighs per hour.

The body sighs in order to inflate the alveoli – the tiny sacs in the lungs where oxygen enters and carbon dioxide leaves the bloodstream.

If we did not sigh, the aveoli would eventually collapse causing lung failure.

Sighing is vital to lung function, and thus to life, said Jack Feldman, a professor of neurobiology at the David Geffen School of Medicine at UCLA and a member of the UCLA Brain Research Institute. ​

“A sigh is a deep breath, but not a voluntary deep breath,” he said. “It starts out as a normal breath, but before you exhale, you take a second breath on top of it.”

And it is a pair of neuron clusters in the brain which are responsible for turning our normal breaths into sighs, according to experts at UCLA and Stanford universities in the US.

Researchers hope that the findings will help doctors to treat patients who cannot breathe deeply without assistance, or who have disorders where they sigh too frequently.

The study published in the digital edition of the ‘Nature’ journal involved testing more than 19,000 gene-expressions on the brain cells of mice.

Around 200 neurons in the brain stem were found to produce and release one of two neuropeptides which allow the organ’s cells to communicate with one another.

These types of peptides are also found in humans, and in mice were highly active in the area of the brain which helps to control the breathing and is also linked to sighing.

Researchers then identified that the peptide alerted a second set of 200 neurons, which increased the breathing rate and cause mice to create a sigh, rising from 40 times to 400 times an hour.

And when the peptides were blocked, the mice stopped sighing.

Mark Krasnow, a professor of biochemistry and Howard Hughes Medical Institute Investigator at the Stanford University School of Medicine, “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.”

“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 behaviours," said Feldman.

Further research is now needed to understand the cause of emotional sighing, as the behaviour increases when you are stressed, said Feldman.

“It may be that neurons in the brain areas that process emotion are triggering the release of the sigh neuropeptides — but we don’t know that.”