Why people lose consciousness: scientists tracked the process

Statistics show that almost 40% of people faint at least once in their lifetime. And yet scientists still do not know exactly what the mechanism of this process looks like when a person experiences a short-term loss of consciousness.

According to the New Atlas, researchers at the University of California, San Diego, have shed some light on it. For the first time, they have identified the exact genetic pathway that connects the heart to the brain, and which triggers the process of loss of consciousness. Scientists are convinced that this opens up the prospect of finding effective treatments for conditions in which fainting is a common and permanent phenomenon.

Traditionally, it was believed that the brain sends a signal to the heart, which reacts quickly to provoke fainting. However, a team of scientists led by Vineet Augustine, PhD, was able to show that this pathway is only half the battle. "We found that the heart also sends signals back to the brain, which can change brain function," Augustine said. He called the work "the first comprehensive demonstration of a genetically defined cardiac reflex that accurately replicates the characteristics of human fainting at the physiological, behavioral, and neural network levels."

The research team focused on the neural mechanisms associated with the Bezold-Jarisch reflex (BJR), a cardiac function discovered in 1867. The BJR was thought to be characterized by a decrease in heart rate, blood pressure and respiration. It was associated with the development of fainting. But so far, it has not been possible to prove it.

Modern researchers have studied the genetic makeup of a sensory cluster known as the nodal ganglion, which is part of the vagal nerves, which transmit signals from the brain to the heart. Here, vagal sensory neurons (VSNs) send signals to the brain stem and are associated with BJR and fainting. Scientists have found that VSNs that express the neuropeptide Y-receptor Y2 (NPY2R) have a significant link to BJR physiology.

Using optogenetics to study specific neurons, the biologists were able to trigger NPY2R in mice VSNs, causing the animals to instantly lose consciousness. Based on the results of their observations, comprehensive data on brain neurons, and machine learning, the researchers from California were able to prove the importance of NPY2R in causing fainting.

Moreover, activation of these neurons caused pupil dilation in experimental mice and eye-rolling, which is characteristic of fainting in humans. In addition, the animals showed a slowing of heart rate and respiration, as well as a drop in blood pressure. "We were amazed to see their eyes rolling at about the same time as their brain activity dropped sharply," the authors of the study shared in their article. They also noted that after a few seconds, brain activity returned to normal. This moment was a breakthrough for them.

When the VSN NPY2R was "turned off" in the mice, BJR and the development of syncope in the mice stopped. Thus, it turned out that the results of previous studies that showed how a decrease in blood flow to the brain causes fainting were inaccurate. Now this data has been supplemented by the understanding that this pathway is a two-way street where the signal is transmitted back to the brain. "Neuroscientists have traditionally thought that the body just follows the brain, but now it's becoming very clear that the body sends signals to the brain, and then the brain changes the function," Augustine explained.

The results achieved by the scientists open up potential opportunities for further research and development of treatments for a number of psychiatric and neurological disorders that have a clear connection between the brain and the heart. Augustine's team also hopes to take a closer look at cerebral blood flow and nerve pathways in the brain at the time of fainting to deepen understanding of this condition.

Earlier, OBOZ.UA shared how scientists learned to restart the brain and speed up learning.

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