Scientists discover how the brain knows when to make you sigh

ANN ARBOR, Mich. – We sigh when we’re content, but we also let out a noisy breath from feelings of relief, exasperation. Sometimes we do it for no reason at all. So how does our brain control all these different types of sighs? A recent study says although one group of brain neurons handles this reaction, the reasons they occur come from all over your brain.

To examine how the brain controls different types of sighs, researchers at the University of Michigan Life Sciences Institute use mice as a study model. Mice are excellent subjects for these tests because they actually have sighs very similar to humans.

Not every sigh is the same

The study in Cell Reports categorizes sighing into two different types: basal and emotional. Basal sighing refers to automatic and unconscious sighs that occur every few minutes. These responses are part of normal breathing and lung function. The other type of sighing refers to reactions triggered by emotions like relief, contentment, or stress.

To study basal sighing, the researchers simply observed mouse breathing patterns in normal conditions. To study emotional sighing, the researchers put mice into a stressful situation by confining them in small, claustrophobic spaces. When mice experience this, they begin to sigh more frequently.

Previous research had identified the group of neurons, known as NMB (neurons expressing Neuromedin B), that control basal sighing. The current study finds that NMB neurons are also involved in stress-related sighing. When researchers artificially silence these brain cells, both kinds of sighs decrease.

Stress plays a key role

The study authors say another group of neurons, known as HCRT (hypocretin-expressing) neurons, send signals to NMB neurons. They are also active when mice sigh due to stress. Unlike NMB neurons however, silencing HCRT neurons only reduces reactions caused by stress. Further, the researchers report HCRT neurons control a mouse’s elevated breathing rate when they are under stress.

“So we’ve found the circuit that regulates all types of sighing, but activates sighs for different reasons using input signals from different parts of the brain,” U-M physiologist Peng Li says in a university statement. “And we found another group of neurons that induces sighing in response to this claustrophobic stress, but also regulates other claustrophobia-related outputs.”

“These findings give us clues about how the brain is wired to control various behavioral and physiological responses to emotions.”

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