People who have looked their mortality in the face often describe their near-death experiences in surprisingly similar terms – vivid recollection of memories, a sense of standing outside of their body, bright lights, or a feeling of tranquility.
While there is plenty of anecdotal evidence from people who have had near-death experiences (NDEs), scientists have little to no data on what happens in the brain as people transition into death. However, under tragic circumstances, scientists have collected the first continuous data on the neural dynamics of the brain during death.
When an 87-year-old patient developed seizures after receiving surgery due to a fall, doctors used electroencephalography (EEG) to monitor his condition; unfortunately, the patient deteriorated and sadly passed away while these recordings were taking place.
Due to the do-not-resuscitate status of the patient, and with the family's consent, the unexpected event allowed scientists to record the electrical activity of a dying human brain. While simplified EEG recordings have been captured from patients withdrawn from life support before, the full placement of recording equipment in this case made for an unprecedented level of detail.
"We measured 900 seconds of brain activity around the time of death and set a specific focus to investigate what happened in the 30 seconds before and after the heart stopped beating," says Ajmal Zemmar, a neurosurgeon at the University of Louisville, US.
"Just before and after the heart stopped working, we saw changes in a specific band of neural oscillations, so-called gamma oscillations, but also in others such as delta, theta, alpha and beta oscillations."
Neural oscillations are the collective electrical activity of neurons firing in the brain, and are more commonly known as brain waves. These waves of electrical activity happen at different frequencies, and various frequency bands have been linked to different conscious states.
Thus, neuroscientists have managed to associate different frequencies of brain waves with specific functions like information processing, perception, consciousness and memory during wakefulness, and states of dreaming and meditation.
Just after the patient suffered the cardiac arrest that led to his death, his brain activity revealed a relative spike in gamma band power that was interacting the most with alpha waves – a pattern not dissimilar to memory recall.
"Given that cross-coupling between alpha and gamma activity is involved in cognitive processes and memory recall in healthy subjects, it is intriguing to speculate that such activity could support a last 'recall of life' that may take place in the near-death state," the team writes.
The authors do note several caveats. Firstly, the patient's brain was in a post-traumatic state that had suffered from bleeding, swelling, and seizures. Additionally, the patient had received large doses of anti-seizure drugs, which might also affect neural oscillatory behavior.
There were also no baseline, 'normal' brain scans of this patient to compare the brain activity to. However, by definition we can't have access to such data in healthy patients whose deaths are impossible to anticipate. Therefore, obtaining recordings of the near-death phase could only come from an already ill patient.
Despite these limitations, the team's findings do point to a potential link between brain waves observed during death with the phenomenological experiences of NDEs, where participants describe their life flashing before their eyes.
What we know about brain waves during memory retrieval points to evidence that the brain may go through a stereotyped activity pattern during death. The authors also note the findings are similar to alterations in neuronal activity that have been observed in rodents during death.
Fascinatingly, the results are consistent with the notion that the brain organizes and executes a biological response to death that may be conserved across species with tied evolutionary lineage and broadly similar neuronal structures.
Although researching what happens to the brain during death can be difficult, especially when patients leave behind distraught family members, Zemmar takes some comfort in the idea that our brains may immerse us in our most beloved memories while we leave the world.
"Something we may learn from this research is: although our loved ones have their eyes closed and are ready to leave us to rest, their brains may be replaying some of the nicest moments they experienced in their lives."
The case report was published in Frontiers in Aging Neuroscience.