The human heart has long been viewed as an organ that faithfully responds to signals from the brain, beating faster or slower according to the body’s needs. New research, however, suggests that the heart possesses a far more sophisticated internal control system than previously understood. According to a study reported by Nature and published in the journal Cell, scientists have identified distinct groups of nerve cells within the heart that help maintain its function during periods of severe stress, challenging the long-held assumption that cardiac neurons perform largely identical roles.
Researchers studying mice found that the heart’s intrinsic cardiac nervous system — sometimes described as the heart’s “little brain” — contains specialised populations of neurons with different responsibilities. The findings provide one of the clearest pictures to date of how the heart’s own nervous system works independently while remaining closely connected to the brain.
“The key is to keep the heart functional no matter what happens. Because if the pump function stops, you will die,” Rui Chang, a neuroscientist at Yale University School of Medicine and co-author of the study, told Nature.
Unlike the brain, whose complex neural networks have been extensively studied, the intrinsic cardiac nervous system has remained poorly understood. Embedded within fatty tissue surrounding the heart, this network communicates continuously with the brain while also processing signals locally. Because cardiac neurons account for only about 0.01 per cent of cells within heart tissue, researchers have faced significant technical challenges in identifying their precise functions.
To overcome those limitations, Chang’s team genetically engineered mice so that every cardiac neuron could be identified and analysed. The researchers then sequenced genes from individual neurons, allowing them to distinguish two genetically different populations before mapping their locations and examining their functions through advanced imaging techniques.
One group, known as Npy+ neurons, proved essential for maintaining normal heart function. Researchers found that stimulating these neurons slowed heart rate, while eliminating them caused heart failure and death in the animals. The results indicate that these neurons help regulate excessive increases in heart rate while remaining indispensable for the heart’s continued operation.
The second population, called Ddah1+ neurons, initially appeared to have little effect. Mice lacking these neurons continued to survive normally, leaving researchers uncertain about their purpose. The breakthrough came unexpectedly during routine blood pressure testing, when a graduate researcher observed a mouse die while its blood pressure was being measured.
Further investigation revealed a striking pattern. According to the study, roughly two-thirds of mice without functioning Ddah1+ neurons died during blood pressure measurements, while animals with intact neurons remained unaffected. Researchers observed that shortly before death the animals experienced a sudden and irreversible drop in heart rate.
The team concluded that stress appeared to trigger the fatal response. When the mice were exposed to other stressful conditions, most animals lacking Ddah1+ neurons again died, suggesting that this specialised group of cardiac neurons protects the heart during periods of physical stress. Conversely, activating the neurons significantly improved survival among stressed mice.
Nature reports that the findings highlight the increasingly recognised role of specialised neural networks outside the brain. Beth Habecker, a chemical physiologist and biochemist at Oregon Health and Science University, told the journal that scientists have come to appreciate that peripheral nervous systems do far more than simply relay instructions from the brain, describing the new findings as a significant expansion of that understanding.
Whether the discoveries translate directly to humans remains uncertain, although researchers noted that the genetic markers identifying the newly discovered mouse neurons have also been detected in human cardiac nerve cells. Kalyanam Shivkumar, a cardiologist at the University of California, Los Angeles, who peer-reviewed the study, told Nature that there would “undoubtedly” be important similarities between the two systems.
The findings may also have practical implications for cardiovascular medicine. Chang said understanding the intrinsic cardiac nervous system is important because of its links to conditions including heart attacks, heart failure and cardiac arrhythmias. Existing treatments such as atrial ablation already target parts of the heart’s nervous system to correct abnormal heart rhythms, but clinicians have had only a limited understanding of the underlying biology guiding those procedures.
Researchers believe the new findings could support the development of more precise interventions, including targeted nerve-based therapies, improved surgical techniques and new drug treatments. Shivkumar told Nature that neuroscience-based therapies are expected to shape a new generation of treatments for heart disease, describing the study as a foundational step in expanding scientific understanding of how the heart’s own nervous system protects one of the body’s most vital organs.
