Kills electronics in brain cells
Death: the last beacon in the brain
The beginning of the end: shortly before a person dies, an electrochemical discharge wave sweeps through the brain like a tsunami. Scientists have now observed this phenomenon in dying patients with a lack of oxygen in the brain. As they report, this wave initiates the brain's dying process, but the process is reversible to some extent.
Of all the organs in the body, the brain is the most sensitive to oxygen starvation. If its blood supply stops - for example after a cardiac arrest - the brains of animals stop their activity after just 20 to 40 seconds - it is in energy-saving mode. When the last reserves are used up, the energy-dependent ion and voltage gradient between the interior of the nerve cells and their environment collapses.
We know from studies with animals that this happens in the form of an electrochemical wave. This discharge wave, known as “spreading depolarization”, spreads in the brain after cardiac arrest like a water wave after a stone is thrown into a lake. This discharge is reversible up to a certain point in time, but if the lack of blood in the brain lasts longer, the brain cells are irreversibly damaged and die.
Wave also in humans?
Jens Dreier from the Charité in Berlin and colleagues have now proven that this last rebellion also occurs in humans. They benefited from the fact that doctors today sometimes implant electrodes in the skull of patients with severe strokes or head injuries in order to be able to better monitor brain activity.
When nine such patients were dying and the life-support measures were ended - at the request of the patient or their relatives - the scientists were able to record the last brain signals of the dying thanks to these electrodes.
Different stages of dying
After the machines were switched off, the patients' blood pressure slowly fell and the oxygen supply to the brain dried up. After the blood flow there had dropped to 20 percent, it only took a few minutes for the entire brain to suddenly stop its electrical activity.
An average of one to two minutes later, the first electrode recorded a signal - the wave had started. It then slowly spread through the brain. It is known from animals that it migrates through tissue at two to five millimeters per minute. Six of the nine patients followed this pattern.
“We were able to prove that the terminal scattering polarization is comparable in humans and animals,” explains Dreier. "Unfortunately, research into this elementary process of damage development in the central nervous system has been neglected for decades because it was wrongly assumed that it does not occur in humans."
The wave is reversible
However, the phenomenon is not necessarily fatal, in many of the patients multiple waves were recorded within days. "It is important that the process - up to a certain point - is reversible when the blood circulation is restored," says Dreier. In this case, the nerve cells recover completely. However, if the oxygen remains cut off, after a minute the point can come when there is no turning back and the neurons die.
But what does this new discovery mean for the future? “Today there are still no direct applications for patients,” says Dreier. “Above all, the slowness of the wave, which makes it difficult to recognize it in the normal EEG, poses a challenge. However, the discovery could lead to improved diagnostics and treatment in the future, in line with Max Planck's motto that recognition must precede use. "(Annals of Neurology, 2018; doi: 10.1002 / ana.25147)
(Charité - Universitätsmedizin Berlin, 02.26.2018 - YBR)February 26, 2018
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