Humans sigh hundreds of times a day – sometimes due to exhaustion, frustration or feelings of relief — sometimes for no reason at all. But there may be more to this life-saving function than you realize. A recent study published in Cell Reports revealed how our brain signals that it’s time to sigh and why.
A 2016 study found that sighing, as simple as it may seem, is actually a necessary function for survival. Our lungs contain over 500 million tiny, balloon-like structures called alveoli. Over time, these structures collapse and struggle to re-inflate — this is where sighing comes in.
“A sigh is a deep breath, but not a voluntary deep breath. It starts out as a normal breath, but before you exhale, you take a second breath on top of it,” study researcher Jack Feldman said. “When alveoli collapse, they compromise the ability of the lung to exchange oxygen and carbon dioxide. The only way to pop them open again is to sigh, which brings in twice the volume of a normal breath.”
The study concluded that it’s necessary to sigh every 5 minutes or so to inflate the alveoli and avoid lung failure.
For most people, our brain signals this reaction automatically and it is part of the normal breathing process. This is known as basal sighing. However, there are many other reasons that sighs occur as emotional responses, from stress and frustration to relief.
A recent study from the University of Michigan aimed to identify how the brain handles this reaction for different scenarios.
“We want to understand how all of these diverse inputs, both emotional and physiological, lead to the same behavioral output,” Peng Li, a physiologist and assistant professor at the University of Michigan Life Sciences Institute said.
Researchers used mice as a study model because the architectural structure of mice’s brains is similar to humans.
The mice were observed both in normal conditions, as well as stressful conditions. Researchers noticed that when placed in stressful situations, confined to a small, claustrophobic space, the mice began to sigh more frequently.
Through previous research, it had been discovered that one group of neurons, known as neurons expressing Neuromedin B (NMB) were involved in all forms of sighing – both basal and emotional. However, the study authors were able to identify another group of neurons, known as hypocretin-expressing neurons (HCRT), that control the elevated breathing rate when 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,” Li said. “And we found another group of neurons that induces sighing in response to this claustrophobic stress, but also regulates other claustrophobia-related outputs.”
There is still more research to be done, but Li said this could be a good first step to understanding the link between the brain and lung functions more.
“These findings give us clues about how the brain is wired to control various behavioral and physiological responses to emotions,” Li said.