What happens in the brain on the verge of death? For hundreds of years, stories told by people who have come back from the brink have generated theories and questions. From the rapid review of important life events to out-of-body experiences, these accounts hint at ongoing brain activity even as the body’s systems shut down. A new study, published in the Proceedings of the National Academy of Sciences, offers a glimpse into what is going on in the brain during the dying process.
Neuronal Activity After the Last Heartbeat
Medically speaking, the end of cardiac activity marks the end of life. However, studies suggest that brain activity can persist. Research in rats, for example, has demonstrated signs of consciousness 30 seconds after the last heartbeat. “We have this binary concept of life and death that is ancient and outdated,” said Sam Parnia, a pulmonologist at New York University Langone Medical Center.
Attempting to expand on knowledge of human brain activity during the dying process, researchers led by Jimo Borjigin, a neurologist at the University of Michigan School of Medicine, studied end-of-life neuronal activity in four comatose patients on life support. The patients had no chance of survival. Electroencephalography caps were used to monitor the electrical activity in each patient’s brain. The researchers recorded activity before and after the removal of ventilators, during the last measurable heartbeat, and until brain activity ceased.
Just after ventilator removal, two of the patients exhibited a sudden burst of high-frequency gamma wave activity, which persisted as their hearts stopped beating. The same activity patterns, in healthy people, have been associated with conscious processes such as memory recall, learning, and dreaming. The results showed heightened electrical activity in the temporo-parieto-occipital junction, a brain region associated with consciousness and activated during dreaming, seizures, and out-of-body hallucinations. Borjigin noted that the two people whose brains exhibited the continued activity had a history of seizures, which could be a factor in the phenomenon.
Entering Survival Mode
Borjigin suggested that the burst of brain activity could be a sign of the brain entering survival mode after the oxygen supply is cut off. Studies of brain death in animals have shown that the process prompts the release of signaling molecules and generates atypical brainwave patterns to try to restore itself, even as it shuts down external signs of consciousness. “It shuts the door to the outside world and takes care of internal business because the house is on fire,” she said.
Insights Into Consciousness
The gamma wave activity is believed to indicate that different regions of the brain are attempting to coordinate to integrate varied sensory experiences into conscious awareness. How the brain does this, says, Ajmal Zemmar, a neurosurgeon at the University of Louisville, “is one of the biggest mysteries in neuroscience.” Observing these waves in dying individuals suggests a possible biological mechanism underlying the reported phenomenon of people experiencing a flashback of memories during the final moments of life. Notably, prior research identified similar gamma waves in a person who experienced a heart attack while their brain was being monitored for seizures.
Future Research and the Quest for Answers
Building on these findings, Borjigin hopes to further investigate end-of-life brain activity in collaboration with other researchers. Studies to understand what’s happening in the brain and the dying process are important, according to Zemmar. “Death is sort of a mystery—we don’t really know what it is.”
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