Summary: Study reveals a potential link between respiration and neural activity changes in animal models.
Source: Penn State
Mental health practitioners and meditation gurus have long credited intentional breathing with the ability to induce inner calm, but scientists do not fully understand how the brain is involved in the process.
Using functional magnetic resonance imaging (fMRI) and electrophysiology, researchers in the Penn State College of Engineering identified a potential link between respiration and neural activity changes in rats.
Their results were made available online ahead of publication in eLife. The researchers used simultaneous multi-modal techniques to clear the noise typically associated with brain imaging and pinpoint where breathing regulated neural activity.
“There are roughly a million papers published on fMRI—a non-invasive imaging technique that allows researchers to examine brain activity in real time,” said Nanyin Zhang, founding director of the Penn State Center for Neurotechnology in Mental Health Research and professor of biomedical engineering.
“Imaging researchers used to believe that respiration is a non-neural physiological artifact, like a heartbeat or body movement, in fMRI imaging. Our paper introduces the idea that respiration has a neural component: It affects the fMRI signal by modulating neural activity.”
By scanning the brainwaves of rodents in a resting state under anesthesia using fMRI, researchers revealed a network of brain regions involved in respiration.
“Breathing is a need common to almost all living animals,” Zhang said. “We know breathing is controlled by a region in the brainstem. But we did not have a complete picture of how other regions in the brain are impacted by respiration.”
In tandem with fMRI, the researchers used neuronal electrophysiology, which measures electrical properties and signals in the nervous system, to link breathing with neural activity in the cingulate cortex—a brain region in the center of the cerebral hemisphere associated with emotional response and regulation.
Using fMRI and electrophysiology simultaneously allowed researchers to tease out non-neural related fMRI signal changes during data collection, such as movement and carbon dioxide exhalations.
The findings provide insight on how neural activity and fMRI signals are linked at the resting state, Zhang said, which could inform future imaging research on understanding how neurovascular signals change while at rest.
“As the animals breathed, we measured how their brain activity fluctuated with their breathing rhythm,” Zhang said. “When extended to humans, this approach could provide mechanistic insights into how breathing control common to meditation practices may help reduce stress and anxiety.”
The correlation between neural activity in the cingulate cortex and breathing rhythm may indicate that breathing rhythms may impact emotional state, according to Zhang.
“When we are in an anxious state, often our breathing speeds up,” Zhang said. “In response, we sometimes take a deep breath. Or when we are focusing, we tend to hold our breath. Those are signs that breathing can impact our brain function. Breathing allows us to control our emotions, for example, when we need our brain function to alter. Our findings support that idea.”
Future studies may focus on observing the brain in human subjects while they are meditating to analyze the more direct connection between slow, intentional breathing and neural activity, according to Zhang.
“Our understanding of what is happening in the brain is still superficial,” Zhang said. “If researchers replicate the study on humans using the same techniques, they might be able to explain how meditation modulates neural activity in the brain.”
About this neuroscience research news
Original Research: Open access.
“Neural underpinning of a respiration-associated resting-state fMRI network” by Wenyu Tu et al. eLife
Neural underpinning of a respiration-associated resting-state fMRI network
Respiration can induce motion and CO2 fluctuation during resting-state fMRI (rsfMRI) scans, which will lead to non-neural artifacts in the rsfMRI signal. In the meantime, as a crucial physiologic process, respiration can directly drive neural activity change in the brain, and may thereby modulate the rsfMRI signal.
Nonetheless, this potential neural component in the respiration–fMRI relationship is largely unexplored. To elucidate this issue, here we simultaneously recorded the electrophysiology, rsfMRI, and respiration signals in rats.
Our data show that respiration is indeed associated with neural activity changes, evidenced by a phase-locking relationship between slow respiration variations and the gamma-band power of the electrophysiological signal recorded in the anterior cingulate cortex.
Intriguingly, slow respiration variations are also linked to a characteristic rsfMRI network, which is mediated by gamma-band neural activity. In addition, this respiration-related brain network disappears when brain-wide neural activity is silenced at an isoelectrical state, while the respiration is maintained, further confirming the necessary role of neural activity in this network.
Taken together, this study identifies a respiration-related brain network underpinned by neural activity, which represents a novel component in the respiration–rsfMRI relationship that is distinct from respiration-related rsfMRI artifacts. It opens a new avenue for investigating the interactions between respiration, neural activity, and resting-state brain networks in both healthy and diseased conditions.