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The Heart-Brain Connection: Researchers Identify the Mechanisms behind Fainting

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The Heart-Brain Connection: Researchers Identify the Mechanisms behind Fainting

New Study Reveals Relationship Between Heart and Brain in Fainting

Nearly 40% of people experience syncope or fainting at least once in their lives, resulting in a significant number of hospital emergency room visits. However, the exact mechanisms behind fainting have remained a mystery.

In a groundbreaking study, researchers at the University of California, San Diego, in collaboration with colleagues at the Scripps Research Institute and other institutions, have uncovered the relationship between the heart and the brain in fainting episodes. The findings could have implications for better understanding and treating psychiatric and neurological disorders related to brain-heart connections.

Lead author of the study, Professor Vineet Augustine, reimagined the heart as a sensory organ, challenging the traditional view that the brain sends signals and the heart simply follows instructions. The team discovered that the heart also sends signals to the brain, which can influence brain function.

Published in the journal Nature, the study examined the Bezold-Jarisch reflex (BJR), a cardiac reflex first described in 1867. Previous hypotheses suggested that the BJR, characterized by increased heart rate, blood pressure, and breathing, may be linked to fainting. However, information was lacking to confirm these theories due to limited understanding of the neural pathways involved.

The researchers focused on the genetics of the sensory cluster known as knotty ganglia, which form part of the vagus nerves responsible for transmitting signals between the brain and visceral organs, including the heart.

To proactively activate the vagal sensory neurons, the team developed a method to stimulate and control the neurons in mice. Surprisingly, the mice immediately fainted upon stimulation. During these episodes, the researchers recorded brain activity, cardiac activity, and changes in facial features such as pupil diameter and whisker movements.

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The results revealed that the activated neurons caused rapid pupil dilation, eye-rolling similar to human fainting, as well as suppressed heart rate, blood pressure, and respiratory rate. The researchers also observed reduced blood flow to the brain, an area of collaboration with Professor David Kleinfeld’s lab at UC San Diego.

“We were shocked to see their eyes roll back in their heads simultaneously with a rapid decrease in brain activity,” the researchers reported. “After a few seconds, brain activity and movement returned. This was our eureka moment.”

The discovery challenges the conventional belief that the body merely follows the brain’s instructions. Instead, it highlights that the body can send signals to the brain, leading to changes in brain function.

The comprehensive demonstration of the cardiac reflex at various levels, including physiological, behavioral, and neural networks, opens up new possibilities for investigating syncope and related disorders. The insights gained from this study can help pave the way for innovative treatment approaches in the future.

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