The mind and body regulate breathing and vice versa at the cellular level. More than 25 years ago, researchers ... discovered a small bundle of about 3,000 interlinked neurons inside the brainstems of animals, including people, that seem to control most aspects of breathing. They dubbed these neurons the breathing pacemaker. Recently, a group of scientists ... began using sophisticated new genetics techniques to study individual neurons in the pacemaker. They eventually identified about 65 different types of neurons ... with a unique responsibility for regulating some aspect of breathing. For the newest study... researchers carefully disabled [a] type of breathing-related neuron in mice. Afterward, the animals at first seemed unchanged. But when the mice were placed in unfamiliar cages, which normally would incite jittery exploring and lots of nervous sniffing - a form of rapid breathing - the animals instead sat serenely grooming themselves. "They were, for mice, remarkably chill," says Dr. Mark Krasnow, a professor of biochemistry at Stanford who oversaw the research. It turned out that the particular neurons in question showed direct biological links to a portion of the brain that is known to be involved in arousal. This area sends [directs] us to wake up, be alert and, sometimes, become anxious or frantic. In the mellow mice, this area of the brain remained quiet. The implication of this work ... is that taking deep breaths is calming because it does not activate the neurons that communicate with the brain's arousal center.