Researchers have identified a brain mechanism that may help explain how the body switches between rest and action, offering potential clues for conditions including Parkinson’s disease and alcohol use disorder.
The study, led by Rutgers University-New Brunswick, examined how the brain controls autonomic arousal — the involuntary response of the sympathetic nervous system to neutral, stressful, threatening or emotional stimuli.
Autonomic arousal affects physiological responses such as heart rate, pupil size and other measures that prepare the body for action.
The findings, published in Science Advances, suggest that the anterior cingulate cortex, a frontal brain region involved in cognitive control, acts like a “dial” that regulates the strength of these responses.
Rafiq Huda, assistant professor in the Department of Cell Biology and Neuroscience at Rutgers School of Arts and Sciences, said: “What we’ve discovered is the region in the brain that can control the gain of these autonomic responses for movement and environmental stimuli.
“It acts as a dial to mediate how strongly our heart rate and other measures of sympathetic tone, like the pupil diameter, respond in these situations.”
The research team studied mice to model how the human brain responds during movement and sensory stimulation.
They focused on two brain regions: the locus coeruleus, a brainstem nucleus that releases the neurotransmitter norepinephrine, and the anterior cingulate cortex.
Previous research has linked the locus coeruleus to triggering autonomic arousal, but the role of the anterior cingulate cortex has been less clear.
To investigate, researchers used viral tools and implanted tiny fibre optics into the brains of mice.
In some experiments, the fibre optics delivered pulses of light to switch brain activity on or off in real time. In others, they allowed researchers to record brain activity linked to autonomic changes.
The team also used a video camera and custom machine vision software to track changes in the animals’ pupils, which were used as a measure of sympathetic tone.
In both humans and mice, pupil size can change before movement begins and continue to increase as activity intensifies.
The researchers found evidence that the locus coeruleus and anterior cingulate cortex work together to trigger and regulate arousal.
When activity in the anterior cingulate cortex was switched off, the arousal response was suppressed.
When activity in the region increased, pupil dilation rose dramatically and mice were even prompted to start moving.
Huda said further research is needed to understand how the findings may relate to movement disorders and stress-related behavioural conditions.
However, the discovery could have implications for Parkinson’s disease, where one of the major symptoms is difficulty initiating movement.
Huda said: “One of the major symptoms of the disease is an inability to start moving.
“If there is a dysfunction in processes that connect your intention to move to preparing your body to enact those movements, it might help explain the disease’s most debilitating symptoms.”
Future studies will examine whether changes in autonomic regulation by the anterior cingulate cortex could contribute to mobility challenges in Parkinson’s disease.
The findings may also have relevance for alcohol use disorder.
Because alcohol use is often associated with stress and high baseline sympathetic tone, Huda’s team is investigating whether the anterior cingulate cortex could be targeted to help control cravings or reduce dependence.
The work is being supported by a National Institutes of Health grant.
Huda said: “We believe our findings will be transformative, not only for researchers working on arousal and the prefrontal cortex but broadly for scientists interested in cortical information processing and cortical-subcortical interactions in both health and disease.”