After cardiac arrest: what the brain does when you die

What happens in the brain when we die after our heart has stopped and oxygen starvation sets in? Scientists have long assumed that the thinking organ then hardly works anymore. However, a small retrospective pilot study recently provided evidence that a short but strong brain wave activation in the gamma frequency band can occur again in different brain areas in dying people. In parallel with this sudden brain activity, her heart beat faster.

Researchers led by Jimo Borjigin from the University of Michigan School of Medicine observed this in two out of four patients in an intensive care unit. They published their results in the journal “PNAS” (Proceedings of the National Academy of Sciences). A gamma wave activity surge is thought to be a potential biomarker of some sort of inner consciousness. The three contiguous posterior brain areas in which it occurred are considered a type of “hot zone” associated with dreaming, visual hallucinations in epilepsy, and other altered states of consciousness.

The four patients were in a coma after a heart attack in the intensive care unit. Because epileptic seizures can occur in such cases, their brain waves were monitored by electroencephalography (EEG) for early detection and drug treatment. Their heart rate was also monitored. In all four cases, the families then decided to switch off artificial respiration and, in one case, the pacemaker because of the poor health prognosis.

“We know surprisingly little about what happens when you die,” says Borjigin. The only thing that is clear is that in cardiac arrest, outward awareness is lost. Whether one can have an inward, covert consciousness in these moments is unknown, the researchers write. It is also unclear what brain processes could explain the various near-death experiences, from a very bright light to feeling out of body, which up to 20 percent of heart attack survivors reported. These questions helped motivate Borjigin’s research.

“For a long time everyone thought that the brain is at the mercy of the heart and behaves like a silent spectator during cardiac arrest after the heart stops,” says Borjigin. “Our study shows that potentially the opposite is the case. The brain is super activated, as if it were being woken up from within,” the researcher explains. As if it senses that something life-threatening is about to happen.

It’s still unclear what that means and “why you [in diesem Moment] subjective consciousness or subjective perception”. The researcher wonders whether it could be a more extreme form of the process when you are woken up by the brain at night because you have had breathing pauses due to sleep apnea: “Is this gamma increase an attempt of the brain to ensure you survive this ordeal?”

It is also possible that the brain reacts to the lack of oxygen when dying if it has previously been traumatized by seizures in which breathing can stop. So it could be some kind of post-traumatic stress reaction. Gamma wave activation occurred in those two patients who had had seizures before. However, these did not happen in the last 24 hours before her death.

The other two patients did not experience a sharp rise in gamma or an accelerated heart rate after their ventilators were removed. In one case, the EEG showed patterns of short surges in activity (bursts) with pauses (suppression) in between, implying a poor prognosis. In the second patient, the lack of heart rate increase was probably due to the fact that she had a donor heart.

Transplanted hearts cannot be fully reconnected to the autonomic nervous system, which increases heart rate when exerted or stressed. Because this nerve control, also called vegetative or involuntary, could play a role in gamma activation, as Borjigin suspects, this could explain the lack of gamma activation in these two patients.

Borjigin is aware that due to the small number of patients, these results are still very preliminary and cannot reveal what the patients perceived when dying. To understand in detail why the brain shows increased gamma activity when dying and what that might mean, further studies with more patients are needed. Borjigin’s team has already submitted a grant application for data analysis from several dozen patients.

The current study confirmed previous results of Borjigin’s animal experiments with rats. As early as 2013 and 2015, she also published in the journal PNAS that the brains of rodents also show strong gamma wave activation as soon as the researchers – under anesthesia – give them a potassium chloride injection into the organ or let them breathe in carbon dioxide. The former stops the heart, the latter triggers a body-wide oxygen starvation.


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