It’s long been known that the brain has a close relationship to the subtle physiological signals sent out by internal bodily processes such as the heart rate, respiration and muscle system, both driving them and responding to them. The technique called resonant breathing is one example, where deliberately breathing more slowly — about six breaths a minute — aligns breath cycles with the heart’s natural rhythm, creating more balance in the body’s response to its environment, lowering stress and promoting mental and physical health.
Prof. Shella Keilholz
However, research has been scarce on what is happening between the brain and the body to enable resonant breathing to have such a calming effect on the brain.
Keilholz was part of a team of researchers that recently published a study in Nature Neuroscience offering some of the first answers to this question. The study found that the brain produces what they call a global signal — a single master signal linked to multiple body processes in the autonomic nervous system, the system that controls involuntary responses including heart rate, respiratory volume, skin conductance and the diameter of the pupils. Global activity patterns had previously been observed in the brain but until now, they hadn’t been linked to cyclical variations in body processes.
“That view of the global signal as something that might be an actual repeated process in the brain is new,” Keilholz says. “While people have known that we have different autonomic nervous responses for a long time, nobody has put all this together in one coherent system. Our research showed it looks like one coherent system.”
The team studied global signals by looking for connections between variations in brain signals, observed through functional magnetic resonance imaging (fMRI) and variations in multiple body processes, including heart rate, skin conductance, respiratory volume and blood pressure changes. While each of these responded normally to external stimuli, they also showed spontaneous variations that seemed to be coordinated.
Some responses happened a little faster than others, some a little more slowly, but they all followed what Keilholz calls “a global pattern. You get the strong positive amplitude, then the strong negative amplitude and then a return to normal.”
The autonomic nervous system has long been known to play an important role in maintaining the equilibrium of different body processes. Keilholz says it isn’t yet clear just how the subtler, harder-to-detect global signal connects to different bodily processes or what overall role that signal plays.
“It's possible that the autonomic nervous system is not purely functional, but it also responds to the body's internal needs as an entire system,” she says. “That might be what we're seeing here: not a major change, but just enough of a wobble to measure and maybe influence behavior.”
Possible uses in treating psychological disorders
Even without understanding its function, Keilholz thinks it’s useful to ask whether the newly discovered signal behaves the same way in people with neurological and psychiatric disorders.
“Especially psychiatric disorders,” she says, “because there’s work showing that meditation can sometimes help with conditions like depression. I don’t think paced breathing is going to be a cure for depression. But a lot of things have an adjacent effect to therapy and help improve outcomes for people so I think it’s worth exploring. Since a lot of natural interventions like exercise seem to be effective, this seems like a promising direction.”