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Take a deep breath. That’s routine advice for how to calm down or slow down. Yoga instructors, therapists, parents, and even elementary school teachers use long, slow breathing exercises to instill tranquility or reduce . Now, researchers at Stanford University School of Medicine are giving the same advice, with brand-new to back it up. In a recent study, they and their colleagues have uncovered a direct and powerful connection in the brain between breathing and states of mind.

Breathing is automatic, of course. It’s controlled by one of the oldest parts of the brain, the medulla in the brainstem. If we stop breathing for long, we die. Yet we can exert exquisite control over the way we breathe. We can hold our breath, slow it down in or speed it up in childbirth to help us deliver a baby. , gasping, sighing, sobbing, and even speaking are all forms of breathing.

“The power of breathing has assumed almost legendary status in the world of ,” says Mark Krasnow, a professor of biochemistry at Stanford and senior author of the study, which was published last week in Science. Until now, however, no one knew for sure why slow breathing has a calming effect. Or, for that matter, why faster breathing has the opposite effect. Most scientists, including Krasnow, assumed it was probably indirect—perhaps linked to increases in oxygen intake, or metabolic changes in the brain.

The new discovery concerns an area called the “breathing pacemaker.” That pacemaker, officially called the preBötzinger complex, was identified in mice 25 years ago by neurobiologist Jack Feldman at UCLA, who collaborated on the new research. It has since been found in humans. Unlike the cardiac pacemaker, which is in the heart as you might expect, the breathing pacemaker is in the brain. It consists of about 3,000 neurons in the medulla.

Researchers have been working to identify those neurons and their roles. One of Krasnow’s graduate students, Kevin Yackle, now at the University of California, San Francisco, analyzed the neurons genetically and found that the pacemaker’s 3,000 brain cells can be grouped into 65 subtypes. In an earlier study, Yackle discovered that one of those subtypes, encompassing some 200 neurons, directly controls sighing in mice. Activate those neurons and the mice start sighing. Inactivate them and the mice never sigh. (In both mice and men, a sigh is a double-sized breath.)

In the new study, Yackle singled out another set of neurons, 175 this time, and inactivated them. Yackle, Krasnow and their colleagues thought they would find the same sort of effect as with sighing. Instead, nothing happened. “It was actually very disappointing initially because the breathing patterns did not change,” says Krasnow. But Yackle kept watching the mice, and he noticed that while their breathing hadn’t changed, their behavior had. “The mice had become chill,” says Krasnow. “They were laid back.”

Usually, when put in a new environment, like the chamber for measuring their breathing, mice explore by sniffing all around. These mice just hung quietly in the corner and groomed themselves, which Krasnow says, is “the kind of thing mice do when they’re calm and relaxed.”

What Yackle eventually determined is that the 175 neurons he had inactivated extend from the pacemaker to the brain’s arousal center, the locus coeruleus. That arousal center tells the rest of the brain whether to wake up or chill out, depending on what’s going on. Like the dashboard of your car letting you know to get gas or air in your tire, these neurons appear to monitor the other neurons in the breathing pacemaker and then tell the brain whether it needs to respond. Just as you would keep driving until you ran out of fuel without a gas gauge, without that neural signal, mice put in a new environment might as well be home in their nests. It’s likely that the same setup will be found in humans.

“We now know that the breathing center directly controls the activity of higher order brain functions,” says Krasnow. “There’s a feedback circuit. Now we can understand better how this control of the breathing center changes the rest of the brain.” Beyond helping all of us in our everyday lives, the research could someday lead to therapies for deadly problems like or Sudden Infant Death Syndrome (SIDS).

For those who’ve long believed in the powerful effects of breathing, this is proof they were right. For those who were skeptical, like Krasnow himself, this is hard evidence that changing your breathing can change your state of mind. If you want to wake yourself up, try speeding up your breathing. And if you need to calm down, you really should take a deep breath. It’s just what the neuroscientists ordered.