Take a deep breath, it's all in the brain

New Delhi, April 13: Scientists have pinpointed a cluster of cells in the brain that connects breathing and the mind and may explain how and why controlled, deep breathing can induce calmness, a phenomenon known for centuries but largely unexplained until now.

The researchers in US academic institutions have identified a subpopulation of about 175 neurons in the brain's breathing centre called the pre-Botzinger complex (PBC) that links respiratory activity to relaxation as well as tension and arousal.

Slow, controlled deep breathing has long been used by practitioners of pranayama yoga other meditation techniques and is even prescribed by physicians to suppress excessive excitement or panic attacks, but the precise mechanisms linking breathing with the mind remained unclear.

"This study is intriguing because it provides a cellular and molecular understanding of how that might work," Mark Krasnow, professor of biochemistry at Stanford University who led the research, said in a release. The study's findings have been published in the US journal Science.

Despite the mystery about the underlying mechanisms, physicians have recognised the capacity of deep breathing to induce relaxation and even assessed its use in treating anxiety, depression and pain perception.

Krasnow and his colleagues found that when they eliminated a specific subtype of neuron in the PBC of mice, using genetic engineering tricks, the behaviour of the mice changed from active exploratory movement to calm behaviour such as sitting still or grooming. All other major breathing patterns in these mice remained intact.

"The PBC appears to play a key role in the effects of breathing on arousal and emotion, such as seen during meditation," said Jack Feldman, professor of neurobiology at the University of California, Los Angeles, and a co-author of the study.

The scientists believe the neuronal circuit connecting breathing to the state of the mind they have detected in mice may also exist in humans, pointing out that fast and erratic breathing in humans increases alertness and can cause anxiety and even panic.

Neurobiologists believe the findings may help in the search for new treatment for certain breathing disorders.

"Such information may help us understand the patho-physiology of complex breathing related disorders where arousal is affected," said Bindu Kutty, professor and head of neurophysiology at the National Institute of Mental Health and Neurosciences, Bangalore, who was not associated with the study.

"For example, breathing disorders such as obstructive sleep apnoea or sudden infant death syndrome due to inadequate arousal response after asphyxiation could be due to defective projections from the PBC to other areas of the brain," Kutty told The Telegraph.

Last year, Krasnow and Feldman had identified another set of neurons in the PBC responsible for turning normal breaths into a sigh which, the researchers point out, is vital to lung function and thus to life. A person, on average, sighs every five minutes.

"A sigh is a deep breath, but not a voluntary deep breath," Feldman had said after their discovery of the sigh-linked neurons last year.

A sigh inflates the alveoli, the tiny balloon-like sacs in the lungs where oxygen enters and carbon dioxide leaves the bloodstream. Sometimes, the alveoli collapse and sighs help open them.