'A Sigh is Just a Sigh' Debunked: Scientists Discovered How & Why People Sigh

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In a study published Monday in Nature, scientists have uncovered the brain mechanism that makes one sigh. Sighing is actually a life-sustaining reflex that keeps your lungs from collapsing.

This week, researchers from University of California at Los Angeles and Stanford University collaborated to describe the mechanism of sighing for the very first time, identifying the exact location in the brain from which the sighs originate, reports The Washington Post.

The team identified two tiny clusters of neurons in the brain stem that automatically turn normal breaths into sighs. This happens when your lungs need some extra help and this happens every five minutes or approximately 12 times in an hour, according to the study. This happens regardless if an individual is deep into thinking something depressing.

This can be tested for yourself by lying down in a quiet room and paying close attention to your breathing, reports LA Times. You will notice that the body takes an inhalation once every five minutes and before the exhale, it adds another inhalation on top of it.

These types of inhalation are not related to emotion, said Jack Feldman from UCLA. It is actually a reflex action that provides an extra amount of air that helps re-inflate some of the 500 million tiny balloon-like sacs in the lungs called alveoli.

The alveoli are the places where oxygen enters the bloodstream and where carbon dioxide is removed. It is said that, the sack, when put all together, can span as large as a tennis court even though each individual sack is just 2/10th of a millimetre in diameter.

The only way to op them open again when they collapse is when you sigh, researchers said. This brings in twice the volume of the normal breath, Feldman said to LA Times.

However, the discovery of how the brain turns a normal breath into a sigh was discovered by two different lines of inquiry from Feldman's lab at UCLA and biochemist Mark Krasnow's lab at Stanford.

Feldman identified a kind of neuropeptides that controls sigh rates in mice in his laboratory. Neuropeptides are protein-like molecules that brain cells use to communicate with one another.

When scientists injected the peptide called bombesin into the mice, they went from sighing 40 times an hour to sighing 400 times an hour. While killing the cells with the receptor for the peptide made the mice stop sighing altogether, there were no interruptions in their breathing patterns.

Several years later, Kevin Yackle, a student of Krasnow at Stanford investigated what molecules are highly expressed in regions in the brain associated with breathing. After screening more than 19,000 gene expression in animals, he found two small populations of neurons that produce this neuropeptide.

The researchers might later on look to any possibility if higher regions of the brain that control emotions could also produce bombesin-related peptides that can trigger sighing when feeling stressed out or unhappy.

Check out this video about another study on sighing: