Scientists have been able to determine for the first time the sequence of events that occur in the brain when the organ turns off and we die.
They discovered what they call a “death wave” – a flood of chemicals sweeping through the brain, followed by a wave of electricity, and then nothing.
Lead author Severine Mahon, a neuroscientist at the Paris Brain Institute in France, told DailyMail.com: 'Our work shows that death (not dying) is not an event, but rather a 'long' process that can be reversed up to a certain point. .'
“But we don't know exactly where the tipping point is.”
Death happens in stages. It's not as simple as turning a switch on and off. In multiple stages, waves of chemical and electrical activity flood the brain before all functions cease
To investigate what the process of death looks like in the brain, the team surgically implanted tiny probes into clusters of brain cells and individual neurons in the brains of mice.
These tools measured electrical and chemical activity in the brains of mice as they died.
Their results show how death is not as simple as we think.
It's not just switching from “on” to “off,” it's a step-by-step process of cells and regions turning off in different ways and emitting unique signals as they do so.
The exact “point of no return” — when our consciousness turns off and can't return — is still up for debate, but understanding how and where the “death wave” occurs could help doctors develop better drugs or treatment strategies to prevent brain damage. In the event of a serious infection, the researchers behind the new work said.
there Raw time windows Recent research has shown that when a dying brain can be resuscitated, it is not a quick and decisive cut-off point.
Restoring breathing soon enough can reverse the brain's shutdown process, enabling neurons to start working again. But some cells are more sensitive than others, and will die sooner if not revived
In the new study, anesthetized animals were taken off ventilators while implanted instruments recorded what was happening, both when the animals died and when they were brought back to life.
Activity was assessed in the somatosensory cortex, an area in the outer layer of the brain that processes signals related to temperature, touch, texture, and pain, as well as awareness of the body's location and movement in space. The somatosensory cortex in our brain has a similar role, structure, and location.
When the mice died, scientists noticed the first wave of activity, caused by the chemical glutamate that encourages neurons to fire.
The release of large amounts of glutamate occurred when brain cells, deprived of oxygen, exhausted their stores of ATP, the molecule that gives cells the energy they need to function.
“Before the brain's flat lines, there comes a period of intense cortical activity,” Mahon said.
This increase takes the form of gamma and beta waves, which are brain signals usually associated with conscious experiences.
“We know that in healthy people these brain waves are responsible for memory recall,” Ajmal Zammar, a neurosurgeon at the University of Louisville who was not involved in the research, told DailyMail.com.
“So we wonder whether the same thing happens at the time of death: that you have a memory flashback after your heart stops beating and the brain prepares to undergo death.”
The patient is clearly unconscious when this happens, Mahon said.
She added that some believe this activity is responsible for the near-death experiences people report.
“An alternative hypothesis (our hypothesis) is that near-death experiences occur during the gradual return of cortical activities (similar to those associated with hallucinations) after successful resuscitation.”
Unfortunately, it is difficult or impossible for scientists to know exactly what each part of the death experience feels like.
“Once someone dies, you can't question them,” Zimar said.
After these mysterious waves of activity, brain activity becomes constant. But this is not the end.
This happens when a so-called “death wave” occurs: a powerful wave of electricity radiates through the brain when nerve cells stop working.
That electrical wave, called hypoxia-induced depolarization, signals nerve cell death.
“Like a swan song, it is the true sign of the transition towards a cessation of all brain activity,” said Antoine Carton Leclercq, the study’s first author, a graduate student. statement.
“We already knew that it was possible to reverse the effects of hypoxia-induced depolarization if we could resuscitate the subject within a specific period of time,” Carton-Lekerque said. “We still have to understand in which areas of the brain a death wave is likely to cause the most damage to preserve brain function as much as possible.”
When scientists restored oxygen and blood flow to the mice's brains, the wave of death reversed and activity began again
By comparing electrical activity before and during hypoxia-induced depolarization, they found that the death wave began in cells deep in the somatosensory cortex — but still relatively close to the surface of the brain as a whole — called layer 5.
It has spread upward to the surface and downward to deeper layers.
“We have observed this same dynamic under different experimental conditions and believe it could exist in humans,” Mahon said.
The fact that the death wave originated in layer 5 suggests that these particularly energy-hungry cells may be cut off sooner by the brain, Zimmar hypothesized, as it tries to preserve more important areas — such as cortical layer 2, which is associated with thinking. .
To see if brain function could be restored, they restarted the mice's ventilators and continued to record electrical activity in multiple layers of the brain.
When dying brains were brought back to life, the neurons returned to polarization, the opposite of what happened during the death wave.
As the neurons repolarized, the team found that they produced brainwave signatures that indicated how likely this sensitive organ was to regain function.
Lead researcher Stephane Charpier said: “It has now been proven, from a physiological point of view, that death is a process that takes time, and that it is currently impossible to strictly separate it from life.”
In other words, a death wave does not necessarily mean that the brain is completely dead.
“We now need to determine the precise conditions under which these functions can be restored and develop neuroprotective drugs to support resuscitation in heart and lung failure,” Charpier added.
In most cases in people, restoring breathing within four minutes of cardiac arrest will prevent brain death.
After that, different areas begin to die at different rates – just as in mice.
If doctors could figure out how to prevent a death wave, either by targeting the wave's origin or by limiting its spread, they could help slow or stop the process.
The new study is just the beginning of this research, but finding the source of the problem is the first step toward solving it.
The results appeared in the journal Neurobiology of diseases.
(tags for translation) Daily Mail