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Death: how long do we stay conscious? Does our life really pass before our eyes?


The first time I managed to get past the horror evoked by the concept of death and wondered what it might be like to die, I was around 15 years old. I had just discovered certain atrocious aspects of the French Revolution and how the heads fell there, separated from the body by the guillotine.

A sentence that marked me a lot then and that I remember to this day is that of George Dantonwho, on April 5, 1794, the day of his public execution, said to his executioner “You will show my face to the people, it is worth it”. Some fifteen years later, having become a cognitive neuroscientist, I began to wonder to what extent a brain suddenly separated from the body could still perceive its environment and perhaps even think.

Danton wanted his head shown, but could he see or hear the common people? Had he remained conscious, even for a brief moment? How did his brain stop working?

On June 14, 2021, these questions violently arose again. I had left urgently for Avignon, France, on my mother’s summons because my brother was in critical condition, a few days after being suddenly diagnosed with terminal lung cancer. When I landed in Marseille, I was told that my brother had left four hours earlier. An hour later, I found him on a hospital bed, motionless and handsome, his head slightly turned to the side as if in a deep sleep. Only he was not breathing and his body was cold.

No matter how much I refused to believe it, that day, and for the months that followed, my brother’s extraordinarily brilliant and creative mind had evaporated, and it would only manifest as THE works of art left behind. However, during the last moment that I was able to spend with my brother’s lifeless body, I felt the need to speak to him.

What can brain waves tell us?

And so I did, despite 25 years of brain research and knowing full well that about six minutes after the heart stops and blood flow to the brain is cut off, the brain begins to die. Quickly, the deterioration reaches a point of no return and the basic consciousness – our ability to feel that we are here and now, and that our thoughts are our own – is lost. Could there be something left of my beloved brother’s mind to hear my voice and generate a thought, five hours after he passed away?

Some scientific studies

Scientific studies have been carried out with the aim of better understanding the testimonies of people who have experienced near-death experience. The temporary experience of death has been associated with a feeling of floating out of the body, a feeling of deep happiness, the impression of being called to a beyond, the vision of a light shining beyond on it, but also to deep bouts of anxiety or to absolute emptiness and silence. A major limitation of studies of such experiences is that they overfocus on the nature of the experiences themselves and often overlook the context that precedes them.

Some people who have undergone anesthesia while in good health or who have been involved in an accident resulting in a sudden loss of consciousness have little reason to feel deep anxiety when their brain begins to shut down. On the other hand, someone who has a long history of serious illness or who has life plans in progress could ultimately experience a difficult time. And it also seems fundamental to take into account the spiritual conceptions of the person vis-à-vis biological death.

It’s not easy to get permission to study the biological events that take place in the brain during our last moments of life. A recent article presents an analysis of the electrical activity of the brain in an 87-year-old man who suffered head trauma from a fall as he passed away after a series of epileptic seizures and cardiac arrest. As this is the first publication of such data collected during the transition from life to death, the article remains highly speculative regarding the “mind experiments” that might accompany the transition to death. dead.

The researchers found that certain brain waves, called alpha and gamma, changed rhythm even though the blood had stopped circulating and thus oxygenating the brain. As they write: “Given that the cross-coupling between alpha and gamma activities is involved in cognitive processes and memory access in the healthy individual, one can make the interesting hypothesis that a such activity translates a last life reminder which could take place when death is imminent”.

However, such coupling is far from uncommon in the healthy brain and therefore does not mean that our life is flashing before our eyes at that moment. Furthermore, the study could not answer one of my primary questions: how long after the supply of oxygen to the brain ceases does basic neuronal activity disappear? The article only reports brain activity recorded over a period of about 15 minutes, and only covers a few minutes after death.

In rats, experiences established that after a few seconds, consciousness disappears. And after 40 seconds, the vast majority of neural activity has ceased. Some studies have also shown that this brain shutdown is accompanied a release of serotonina chemical associated with arousal and feelings of well-being.

But what about us? If human beings can be revived after six, seven, eight or even ten minutes in some extreme casescomplete brain shutdown could theoretically take hours.

During my readings, I have come across many theories trying to explain why our lives are flashing before our eyes as the brain prepares to die. Perhaps it is pure artifice associated with the sudden increase in neural activity biologically linked to brain shutdown? Perhaps it is the manifestation of a last resort, a defense mechanism of the body trying to thwart the process of impending death? Or is it still some deep-rooted, genetically programmed reflex that keeps our minds “occupied” as the most difficult event to “live” in our entire existence unfolds?

My hypothesis is somewhat different: if, as I believe, our deepest existential motivation is to understand the meaning of our own existence, seeing our lives flash before our eyes might be the last attempt – however desperate – to find an answer, necessarily at breakneck speed, because time is running out.

Read more: Death: can our final moment be euphoric?

And whether we succeed or not, or even if we are under the illusion of having succeeded, it must lead to a moment of absolute bliss. I hope that future research in this area, looking at more prolonged recordings of neural activity after death, and perhaps invoking brain imaging, will give substance to this idea – that it manifests during minutes or hours, for my brother’s sake, and for all of us.

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