The myth has received a certain scientific justification
The common legend that before death a person's entire life flashes before his eyes has received some scientific explanation. The authors of a study published in the medical journal NEUROSCIENCE recorded a surge in gamma-wave hyperactivity in the human brain in the last minutes of life. So far, this has only been found in rodents.
It is generally accepted that during a cardiac arrest, the brain becomes low-active, that is, it fades and does not show the signs of life that are responsible for our consciousness. However, recent experiments on animals show something completely different: during cardiac and respiratory arrest, they begin to experience a surge in the functional activity of the brain.
Brain function during cardiac arrest is poorly understood. While the loss of explicit consciousness is invariably associated with cardiac arrest, it is unclear whether patients may be latently conscious during the dying process. And yet, almost everyone heard the stories of people who survived the state of clinical death, who described vivid pictures of the supposedly afterlife, or who relived their whole life in a matter of seconds.
Scientists confirm that the so-called near-death experiences, judging by the description of their survivors, are very vivid, «more real than reality», were described in 10-20% of people who survived cardiac arrest. They are characteristic of people from different cultural and religious backgrounds. Moreover, most often these episodes occur during clinical death.
The scientists note that such descriptions represent a biological paradox that challenges our fundamental understanding of the dying brain, which, according to conventional wisdom, no longer functions in such conditions. The data of these people, of course, is subjective, it is impossible to measure them — and until now, these stories of patients who survived cardiac arrest are a mystery.
One of the markers of consciousness is the so-called high-frequency oscillations, and their increase has been previously recorded in patients dying from critical illnesses. Experiments on animals showed the same results: a sudden cessation of cardiac activity or acute asphyxia (suffocation) stimulated a high level of brain gamma activity. However, no studies have yet been conducted that report changes in brain neurons in dying people that could explain the subjective sensations reported by death survivors. The described study is the first.
So, scientists studied the neuronal activity of the brain in dying patients before and after the cessation of mechanical ventilation in the neurointensive care unit of the University of Michigan Hospital. Patients died during EEG monitoring due to cardiac arrest and massive cerebral hemorrhage. All four patients were comatose at baseline with no signs of volitional behavior or any overt consciousness during the last 24 hours of life. Due to a poor neurological prognosis and with the consent of the patients' family members, life support was terminated in all four patients in a coma.
As a result, the researchers found that when ventilatory support was stopped, a global spike in neuronal gamma activity began in some near-death patients. Scientifically speaking, «a pronounced increase in oscillatory activity in the posterior hot zone of the brain» was registered. By the way, the same activity in the brain is observed in healthy people during wakefulness and dreams, as well as in patients with seizures during visual hallucinations, for example, with epilepsy.
“Importantly, the patients showed bursts of functional activity in several frequency bands in the posterior cortical 'hot zone', an area thought to be critical for consciousness processing. This gamma activity was stimulated by global hypoxia (oxygen starvation) and increased as the cardiac condition of dying patients worsened.
These data show that the surge of gamma activity observed in animal models of cardiac arrest can also be observed in individuals in the process of dying,” the authors of the work note.
What a person sees and feels at this time while not clear, but the study lays the groundwork for further exploration of hidden consciousness during cardiac arrest. They also point to the need to re-evaluate the role of the brain during cardiac arrest.
It turns out that the human brain can be active during cardiac arrest, scientists note. And yet, although the pronounced activation of the posterior «hot zone» in the dying brain indicates increased processing of consciousness in these patients, it does not prove it. comments the well-known therapist Alexei Vodovozov. — In 2013, neuroscientists discovered incredible brain activity in rats within 30 seconds of cardiac arrest, and now they've reached humans.
When analyzing the signals in the period between the last measurable heartbeat and the cessation of brain activity, attention was drawn to bursts of neural activity in the form of high-frequency gamma waves, which continued after the cardiac arrest. The phenomenon was observed in only two out of four cases.
The burst of gamma activity was both local, within the temporo-parietal-occipital (TPO) junctions, and global — between the TPO zones and prefrontal areas. In earlier studies, similar activity has been associated with active recall, intense study, or vivid dreams. How true the find is, further research will show.