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The science of sighs

We all sigh. While sighs are often attributed to sadness, anger, frustration, and angst, research indicates that sighing is a natural part of pulmonary function. The average person sighs twelve times per hour, and without those sighs the air sacs inside of the lungs would cave, resulting in serious consequences.

A 2016 study (1) found that physiological tension was reduced when study participants were instructed to take deep breaths after viewing disturbing images. Participants that were instructed to hold their breath did not find the same relief. That relief is the result of a sudden change in respiratory patterns. At nearly two times the volume of a regular breath, a single sigh is a loud, disruptive, and practical way to push your body’s reset button. It’s nature’s built-in bullhorn.

So why do some people seem to sigh a lot more than others? People suffering from anxiety, trauma, or panic disorder may sigh more than the average in order to subconsciously change breathing patterns at a more rapid rate. This coping mechanism is also effective in a controlled situation. If you find yourself feeling anxious, frustrated, or agitated, you can tap into your body’s own stress-relief mechanisms by focusing on your breath, breathing deeply, and exhaling fully. Since this breath is not part of your body’s regular breathing pattern, you will effectively access your stress-coping reserves, down-regulate your body, and be able to refocus both your mind and body. The result? Instant stress relief.

One group of neurons controls various types of sighing, but they receive their instructions from different areas of the brain depending on the reason for the sigh, according to a study scheduled to publish June 16 in the journal Cell Reports (2).

Humans and other mammals sigh automatically once every few moments to maintain proper lung function. This so-called basal sighing is part of the normal breathing process and happens automatically, without us having to think about it. But beyond serving an essential physiological purpose, sighs also occur as behavioral responses to emotions ranging from stress and annoyance to relief.

How do all of these diverse inputs, both emotional and physiological, lead to the same behavioral output ?

Understanding the brain's control of emotions is a central goal of neurobiology and psychiatry, but it is difficult due to the challenges in teasing out emotional brain states and their complex outputs.

Because sighs offer a simple, measurable output from the brain, researchers use them to learn more about how neural circuits communicate to regulate behavioural responses. They identified the neurons and pathways that regulate basal sighing. In this newest study, the researchers traced up from these so-called NMB-neurons (short for neurons expressing Neuromedin B) to see what signals they were receiving when mice were under stress, and found a dozen forebrain regions that send direct inputs to the sigh-control center.

When the mice were confined to a small space, inducing a claustrophobic-like state, their sighing rate increased by two to three times. Using genetic tools, the researchers identified another type of neurons in one of the forebrain regions, called hypocretin-expressing (HCRT) neurons, that were firing under stress and sending signals to the NMB-neurons. The researchers then artificially activated the HCRT-neurons, without confining the mice, and saw the same change in sighing rate.

When the researchers silenced the NMB-neurons, both basal sighing and stress-induced sighing drastically decreased in the mice. When they silenced only the HCRT-neurons, however, only the stress-induced sighing decreased while basal sighing was unaffected.

The researchers found that HCRT-neurons also were responsible for an increased breathing rate when the mice were under confinement stress. Since NMB-neurons only control sighing, and not regular breathing, this finding indicates that the HCRT-neurons are sending signals to other parts of the brain simultaneously to activate different stress-induced behaviors.

So they found the circuit that regulates all types of sighing, but activates sighs for different reasons using input signals from different parts of the brain. And they 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.

Citations:

1. https://pubmed.ncbi.nlm.nih.gov/22634279/

2. Brain circuit of claustrophobia-like behavior in mice identified by upstream tracing of sighing, Cell Reports (2020). DOI: 10.1016/j.celrep.2020.1077790 , www.cell.com/cell-reports/full … 2211-1247(20)30759-2

The science of sighs

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