Try it. Breathe slowly and smoothly. A pervasive sense of calm descends. Now breathe rapidly and frenetically. Tension mounts. Why is that? It's a question that has never been answered by science... until now... in mice.
A study published in Science today describes how researchers led by Stanford molecular biologist Mark Krasnow, MD, PhD, identified a handful of nerve cells in the brain stem that connect breathing to states of mind.
Krasnow has long studied the physiology and regulation of breathing. In recent years, his focus has shifted from the lungs to the brain, spawning a collaboration with Jack Feldman, PhD, a UCLA researcher who nearly three decades ago identified in mice what Krasnow calls "the pacemaker for breathing:" a tiny cluster of neurons linking respiration to relaxation, attention, excitement and anxiety located deep in the brain stem. An equivalent structure has since been found in humans.
This respiratory pacemaker in the brain has tougher job than its counterpart in the heart, Krasnow says. Unlike the heart's one-dimensional slow-to-fast continuum, there are many distinct types of breaths: regular, excited, sighing, yawning, gasping, sleeping, laughing, sobbing.
Krasnow and his teammates wondered if different kinds of neurons within this respiratory control center might be generating each of these breathing types. The investigators used advanced methods to tease apart more than 50 closely related but distinct subtypes of neurons in the mouse respiratory control center.
A year or so ago, Krasnow and his colleagues showed that one of these neuronal subtypes was responsible for generating sighing, and nothing else. It's a little-known fact that mice sigh just like we do -- except more frequently: about 40 times an hour. If you wipe out just these 175 or so neurons in a living, breathing, active mouse, Krasnow's team discovered, that mouse sighs no more.
So the scientists tried their luck again. They knocked out another neuronal subtype in the breathing-control center, expecting to see what kind of breathing the mice would no longer engage in this time around. But the mice didn't stop sighing, or sniffing, or for that matter any other "-ing." They just... sort of... chilled out. Even in exciting novel environments, they evidenced less of the fast, frantic breathing that accompanies, say, exploration and more of the slow, smooth breathing associated with hanging out and being mellow.
From my release about the study:
[R]ather than regulating breathing, these neurons were spying on it instead and reporting their finding to another structure in the brainstem. This structure, the locus coeruleus, sends projections to practically every part of the brain and drives arousal: waking us from sleep, maintaining our alertness and, if excessive, triggering anxiety and distress.
Krasnow and his associates had stumbled on a set of neurons that, crouching like embedded reporters inside the respiratory pacemaker, were firing off dispatches that, thanks to the locus coeruleus' s phenomenal broadcast capabilities, would be read throughout the brain as arousal commands. The more communiques these neurons sent, the more aroused the mouse -- or, presumably, the human -- becomes; the fewer, the more laid back.
Previously: Scientists zero in on brain's sigh-control center, Study shows benefits of breathing meditation among veterans with PTSD and New arterial insights portend potential treatments for life-threatening diseases
Photo by Steve Fisch
