Autonomic nervous system is key driver of global fMRI signal, study finds

The activity of the human brain is known to be closely connected to other physiological signals, such as heart rate and breathing. A study by researchers at the University of California Los Angeles (UCLA) and other institutes reveals that a global spatiotemporal pattern in the brain (i.e. a pattern in brain activity that repeats itself across the brain and over time) is a central component of these brain-body interactions.

The same research team has now set out to further investigate this global signal, in the hope of identifying its underlying physiological and neural origins. Their findings, published in Nature Neuroscience, show that this unified pattern of brain-body activity is in great part driven by the autonomic nervous system, the part of the nervous system regulating arousal and other involuntary bodily functions.

“The inspiration for this project came from our previously published paper in Nature Neuroscience where we described prominent spatiotemporal patterns in brain functional magnetic resonance imaging (fMRI) signals,” Taylor Bolt, first author of the paper, told Medical Xpress.

“Of these patterns there was one that dominates: the pattern known as the ‘global signal.’ It’s easy to see when viewing an fMRI scan: suddenly the brain’s fMRI signal ‘lights up’ with strong activity that seems to cover the entire brain—thus, the reason it’s called the ‘global signal.’”

The primary objective of this recent study by Bolt and his colleagues was to pin-point the underlying physiological and neural sources of the dominant pattern in fMRI signals observed in their earlier work.

To do this, they analyzed human fMRI data collected in previous studies and compiled them into readily available datasets, which are widely used to conduct neuroscience research.

“Most existing datasets are limited—pulse oximeter (PPG) on the finger and respiration belts—while others may collect more comprehensive recordings,” explained Bolt.

“Catie Chang had gathered a comprehensive fMRI dataset with a wealth of physiological recordings that allowed us to track a range of bodily states and tie these back to what’s going on in the brain, particularly the brain’s ‘global signal.’ We also supplemented these analyses with several other fMRI datasets (with associated physiological recordings) to ensure the robustness of our findings.”

The methods employed by the researchers were carefully designed to determine the extent to which the human body’s physiological systems (e.g. heart, lungs, exocrine, etc.) track fluctuations in global fMRI signals. Moreover, if these systems are tightly connected, Bolt and his colleagues wished to determine which of them is responsible for the global fMRI fluctuations they observed.

“We found a robust association between the global fMRI signal and a host of autonomic-driven changes in the body that spanned cardiovascular, pulmonary, exocrine and smooth muscle systems under resting conditions,” said Bolt.

“We also found that these co-fluctuations of brain and body observed at rest are induced by experimental manipulation of arousal, including a cued deep breath and intermittent auditory stimulation. Further, the same brain and body co-fluctuations were observed with spontaneous arousals during sleep (as measured by brief, aperiodic EEG activation).”

Overall, the findings gathered by Bolt and his colleagues suggest that the autonomic nervous system, which plays a central role in the regulation of arousal and wakefulness, is an important source of the global fMRI signal. Similarly, they also indicate that the global signal in the brain is a key component of the autonomic nervous system’s arousal response.

“We would now like to dive into the functional significance of the global fMRI signal in the arousal response—what is it ‘doing’ for us, and what downstream mechanisms (or behaviors) are affected by this phenomena,” added Bolt.

Written for you by our author Ingrid Fadelli, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You’ll get an ad-free account as a thank-you.

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