Why Do We Faint? Understanding What Happens in Our Bodies When We Faint

Berfin Ceren Meray
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Source: https://www.iflscience.com/we-might-fina...

Fainting, an experience almost everyone encounters at some point in their lives, remains a phenomenon that, despite its prevalence, has not been fully deciphered by the scientific community. However, a recent study has shed new light on the enigmatic reasons behind fainting, attributing its occurrence to a genetic connection. This research unveils the underlying mysteries and provides a clearer understanding of the factors that lead to fainting episodes. Dive into the details in our article below. 👇

Fainting, scientifically known as Syncope, is actually a quite common occurrence.

About 40% of people experience fainting at least once in their lives. Fainting can occur due to various situations such as hot weather conditions, seeing blood or needles, and even during a challenging bathroom experience. Among neuroscientists, a prevalent view suggests that during Syncope, the brain sends signals to the heart, and the heart responds accordingly. However, according to a recent study, the heart might be considered as a sensory organ on its own, and the communication between the heart and the brain could be bidirectional.

Assistant Professor Vineet Augustine from the School of Biological Sciences at the University of California, San Diego, states,:

'We found that the heart sends signals to the brain and these signals can alter brain functions.' The research team revisited the Bezold-Jarisch (BJR) reflex, discovered in 1867 and associated with fainting. This reflex is linked to three classic symptoms likely experienced by anyone who faints: a decrease in heart rate, breathing rate, and blood pressure. Although scientists have been aware of BJR for over 150 years, the neural pathways underlying it have only recently been explored.

The research focused on specific nerve cell types called vagal sensory neurons (VSN) in the heart.

VSNs are part of clusters called nodose ganglia, themselves components of the vagus nerve. Experiments conducted on mice revealed that VSNs expressing a protein called neuropeptide Y receptor Y2 (NPY2R) played a crucial role in the fainting response. When scientists stimulated these VSNs using optogenetics, the mice in the experiment suddenly fainted, exhibiting similar symptoms as humans, including rolling their eyes backward and dilating their pupils.

A decrease in heart rate, slowed breathing, and a drop in blood pressure were also observed in mice.

Recordings from thousands of neurons in the brains of mice revealed how brain activity and blood flow rapidly decreased. All of these observations aligned with fainting characteristics in humans. In a summary of the study, scientist Jonathan W. Lovelace mentioned, 'We were surprised to see their eyes rolling back, and the rapid decline in brain activities. A few seconds later, brain activity and movement returned. We thought we might have identified neurons that could trigger Syncope.'

Their suspicions were confirmed when the specific VSNs were removed, resulting in the disappearance of the fainting response.

Researchers hope that this discovery will lead to deeper investigations and targeted treatments for conditions that cause fainting. Neuroscientists have long believed that the brain is the driver behind fainting. However, now that scientists have discovered this new and significant role of the heart, unraveling the mystery of syncope will require collaboration between both cardiology and neurology experts.