Dictionaries usually define death as the end of life or the permanent cessation of life processes. But do we know exactly when this happens? When we look into the precise location of this boundary, we discover that scientific progress has turned it into nebulous terrain, with obvious legal repercussions and implications in fields such as organ donation.
Traditionally, the end of life has been determined with the stopping of the heart and breathing, known as cardiopulmonary death. However, resuscitation techniques have blurred this limit. In the 1950s, the concept of brain death began to be introduced into clinical practice. The fact that life support systems make it possible to artificially maintain blood circulation without brain activity, but not the opposite, has led to the fact that today “there is a broad consensus, at least in the Western world, that human death is ultimately the death of the brain,” according to Giuseppe Citerio, professor of Anaesthesia and Intensive Care at the Bicocca University in Milan, Italy.
But the case is not closed. As Citerio noted at the annual Euroanaesthesia conference held last June in Geneva (Switzerland), brain death still lacks a universal definition, despite the efforts of the World Health Organization to develop precise criteria. “Many of the controversies that surround the determination of death by neurological criteria have not been settled,” said Citerio.
Nowadays, the position of many experts is summed up by seeing biological death not as an event, but as a process. But even with this broader definition, it is a process characterized by numerous unusual phenomena that scientists are still trying to understand.
Near death experiences
One of these phenomena is what is known as a Near Death Experience (NDE). Many people who have had cardiopulmonary resuscitation report common sensations, such as a tunnel, a bright light and a disconnection from the body. Scientists point out that NDEs have a probable origin in neurological changes. According to what neuropsychologist Charlotte Martial of the Coma Science Group at the University of Liege (Belgium) tells OpenMind, the stimulation of certain brain areas can cause extracorporeal sensations due to poor sensory integration. However, Martial continues, “this phenomenon is very complex and its occurrence may probably depend on several mixed causes.”
Curiously, although lights or tunnels are often common elements in NDE narratives, a recent study by Martial, comparing more than 150 testimonials, suggests that there is no common sequence. And since all the participants in the study were francophone, it is not known to what extent the reported sensations can be conditioned by cultural factors. “Some studies have shown that there is no tunnel in Indian testimonies, but other investigations found no difference between cultures,” says Martial. “Further research is needed,” she concludes. To this end, the researcher is interested in receiving NDE stories at firstname.lastname@example.org.
Each death is different
But once the sensations are over, it also does not seem clear that the brain has said its last word. Last March, researchers from the University of Western Ontario (Canada) published a study detailing the brain activity records of four terminal patients for 30 minutes before and 30 minutes after the withdrawal of life support. An interesting conclusion is that each death is different, since electroencephalograms (EEG) did not reveal a common pattern. But the surprise was that one of the subjects continued to show brain activity more than ten minutes after the moment of death, namely delta waves, usually associated with deep sleep.
This is not the only case where brain activity has occurred after death. In 2011, researchers at the University of Radboud (The Netherlands) observed that rats produced a sudden peak of brain activity one minute after their decapitation. Scientists defined this occurrence as “the ultimate border between life and death.” However, the effect described in the Canadian patient was different and much longer, without the researchers being able to explain it.
Stranger still is the phenomenon described by the microbiologist of the University of Washington (USA) Peter Anthony Noble. When he studied the activity of genes during the death of mice and zebrafish, he discovered with surprise that more than a thousand genes “wake up” when the animal’s life has ended—including some that have been silent since the end of embryonic development—and remain active until four days after death.
The significance of this so-called thanatotranscriptome is still obscure. According to what Noble explained to OpenMind, the activation of these genes could be part of the process of spontaneous disintegration of the organism. However, there is a more disturbing possibility, which is that it is the struggle of the body that is trying not to die. “One could argue that some of these pathways have evolved to favour healing or ‘resuscitation’ after serious injury, which would be a possible adaptive advantage,” says Noble. In fact, he adds, many of these genes are related to processes such as the response to inflammation.
So one might wonder if, in addition to brain death and cardiopulmonary death, there is also a molecular death of the organism? “Interesting question,” says Noble. “There is a molecular definition of cellular death, but a molecular definition of organismal death is uncertain.”
It is even possible that the definition of death will become even more blurred in the future. The company Bioquark, based in Philadelphia (USA), is trying to address the reanimation of patients in deep and irreversible comas (equivalent to brain death) who are kept stable with cardiopulmonary and alimentary support. The goal of the ReAnima Project, as explained to OpenMind by Ira Pastor, CEO of Bioquark, is to explore the possibility of “restoring central nervous system form and function” through a combination of regenerative medicine and brain stimulation.
While we wait for projects like that of Bioquark to come closer to making reversible that which today is not, at least we can hold on to one consolation: a recent study from the University of North Carolina (USA) has found that the final messages from terminal patients and from those sentenced to death are more hopeful than might be expected. They are, in fact, more positive than the texts written by volunteers imagining themselves in those situations. “I think that we imagine our last moments incorrectly,” the director of the study, psychologist Kurt Gray, tells OpenMInd. “Meeting the grim reaper may not be as grim as it seems.”