Just as birth certificates note the time we enter the world, death certificates mark the moment we exit it. This practice reflects traditional notions about life and death as binaries. We are here until, suddenly, like a light switched off, we are gone.
But while this idea of death is pervasive, evidence is building that it is an outdated social construct, not really grounded in biology. Dying is in fact a process—one with no clear point demarcating the threshold across which someone cannot come back.
Scientists and many doctors have already embraced this more nuanced understanding of death. As society catches up, the implications for the living could be profound. “There is potential for many people to be revived again,” says Sam Parnia, director of critical care and resuscitation research at NYU Langone Health.
Neuroscientists, for example, are learning that the brain can survive surprising levels of oxygen deprivation. This means the window of time that doctors have to reverse the death process could someday be extended. Other organs likewise seem to be recoverable for much longer than is reflected in current medical practice, opening up possibilities for expanding the availability of organ donations.
To do so, though, we need to reconsider how we conceive of and approach life and death. Rather than thinking of death as an event from which one cannot recover, Parnia says, we should instead view it as a transient process of oxygen deprivation that has the potential to become irreversible if enough time passes or medical interventions fail. If we adopt this mindset about death, Parnia says, “then suddenly, everyone will say, ‘Let’s treat it.’”
Legal and biological definitions of death typically refer to the “irreversible cessation” of life-sustaining processes supported by the heart, lungs, and brain. The heart is the most common point of failure, and for the vast majority of human history, when it stopped there was generally no coming back.
That changed around 1960, with the invention of CPR. Until then, resuming a stalled heartbeat had largely been considered the stuff of miracles; now, it was within the grasp of modern medicine. CPR forced the first major rethink of death as a concept. “Cardiac arrest” entered the lexicon, creating a clear semantic separation between the temporary loss of heart function and the permanent cessation of life.
Around the same time, the advent of positive-pressure mechanical ventilators, which work by delivering breaths of air to the lungs, began allowing people who incurred catastrophic brain injury—for example, from a shot to the head, a massive stroke, or a car accident—to continue breathing. In autopsies after these patients died, however, researchers discovered that in some cases their brains had been so severely damaged that the tissue had begun to liquefy. In such cases, ventilators had essentially created “a beating-heart cadaver,” says Christof Koch, a neuroscientist at the Allen Institute in Seattle.
These observations led to the concept of brain death and ushered in medical, ethical, and legal debate about the ability to declare such patients dead before their heart stops beating. Many countries did eventually adopt some form of this new definition. Whether we talk about brain death or biological death, though, the scientific intricacies behind these processes are far from established. “The more we characterize the dying brain, the more we have questions,” says Charlotte Martial, a neuroscientist at the University of Liège in Belgium. “It’s a very, very complex phenomenon.”
Brains on the brink
Traditionally, doctors have thought that the brain begins incurring damage minutes after it’s deprived of oxygen. While that’s the conventional wisdom, says Jimo Borjigin, a neuroscientist at the University of Michigan, “you have to wonder, why would our brain be built in such a fragile manner?”
Recent research suggests that perhaps it actually isn’t. In 2019, scientists reported in Nature that they were able to restore a suite of functions in the brains of 32 pigs that had been decapitated in a slaughterhouse four hours earlier. The researchers restarted circulation and cellular activity in the brains using an oxygen-rich artificial blood infused with a cocktail of protective pharmaceuticals. They also included drugs that stopped neurons from firing, preventing any chance that the pig brains would regain consciousness. They kept the brains alive for up to 36 hours before ending the experiment. “Our work shows there’s probably a lot more damage from lack of oxygen that’s reversible than people thought before,” says coauthor Stephen Latham, a bioethicist at Yale University.
In 2022, Latham and colleagues published a second paper in Nature announcing that they’d been able to recover many functions in multiple organs, including the brain and heart, in whole-body pigs that had been killed an hour earlier. They continued the experiment for six hours and confirmed that the anesthetized, previously dead animals had regained circulation and that numerous key cellular functions were active.
“What these studies have shown is that the line between life and death isn’t as clear as we once thought,” says Nenad Sestan, a neuroscientist at the Yale School of Medicine and senior author of both pig studies. Death “takes longer than we thought, and at least some of the processes can be stopped and reversed.”
A handful of studies in humans have also suggested that the brain is better than we thought at handling a lack of oxygen after the heart stops beating. “When the brain is deprived of life-sustaining oxygen, in some cases there seems to be this paradoxical electrical surge,” Koch says. “For reasons we don’t understand, it’s hyperactive for at least a few minutes.”
In a study published in September in Resuscitation, Parnia and his colleagues collected brain oxygen and electrical activity data from 85 patients who experienced cardiac arrest while they were in the hospital. Most of the patients’ brain activity initially flatlined on EEG monitors, but for around 40% of them, near-normal electrical activity intermittently reemerged in their brains up to 60 minutes into CPR.
Similarly, in a study published in Proceedings of the National Academy of Sciences in May, Borjigin and her colleagues reported surges of activity in the brains of two comatose patients after their ventilators had been removed. The EEG signatures occurred just before the patients died and had all the hallmarks of consciousness, Bojigin says. While many questions remain, such findings raise tantalizing questions about the death process and the mechanisms of consciousness.
Life after death
The more scientists can learn about the mechanisms behind the dying process, the greater the chances of developing “more systematic rescue efforts,” Borjigin says. In best-case scenarios, she adds, this line of study could have “the potential to rewrite medical practices and save a lot of people.”
Everyone, of course, does eventually have to die and will someday be beyond saving. But a more exact understanding of the dying process could enable doctors to save some previously healthy people who meet an unexpected early end and whose bodies are still relatively intact. Examples could include people who suffer heart attacks, succumb to a deadly loss of blood, or choke or drown. The fact that many of these people die and stay dead simply reflects “a lack of proper resource allocation, medical knowledge, or sufficient advancement to bring them back,” Parnia says.
Borjigin’s hope is to eventually understand the dying process “second by second.” Such discoveries could not only contribute to medical advancements, she says, but also “revise and revolutionize our understanding of brain function.”
Sestan says he and his colleagues are likewise working on follow-up studies that seek to “perfect the technology” they have used to restore metabolic function in pig brains and other organs. This line of research could eventually lead to technologies that are able to reverse damage—up to a point, of course—from oxygen deprivation in the brain and other organs in people whose hearts have stopped. If successful, the method could also expand the pool of available organ donors, Sestan adds, by lengthening the window of time doctors have to recover organs from the permanently deceased.
If these breakthroughs do come, Sestan emphasizes, they will take years of research. “It’s important that we not overexaggerate and promise too much,” he says, “although that doesn’t mean we don’t have a vision.”
In the meantime, ongoing investigations into the dying process will no doubt continue to challenge our notions of death, leading to sea changes within science and other realms of society, from the theological to the legal. As Parnia says: “Neuroscience doesn’t own death. We all have a stake in it.”
Rachel Nuwer is a freelance science journalist who regularly contributes to the New York Times, Scientific American, Nature and more. Her latest book is I Feel Love: MDMA and the Quest for Connection in a Fractured World. She lives in Brooklyn.
These robots know when to ask for help
A new training model, dubbed “KnowNo,” aims to address this problem by teaching robots to ask for our help when orders are unclear. At the same time, it ensures they seek clarification only when necessary, minimizing needless back-and-forth. The result is a smart assistant that tries to make sure it understands what you want without bothering you too much.
Andy Zeng, a research scientist at Google DeepMind who helped develop the new technique, says that while robots can be powerful in many specific scenarios, they are often bad at generalized tasks that require common sense.
For example, when asked to bring you a Coke, the robot needs to first understand that it needs to go into the kitchen, look for the refrigerator, and open the fridge door. Conventionally, these smaller substeps had to be manually programmed, because otherwise the robot would not know that people usually keep their drinks in the kitchen.
That’s something large language models (LLMs) could help to fix, because they have a lot of common-sense knowledge baked in, says Zeng.
Now when the robot is asked to bring a Coke, an LLM, which has a generalized understanding of the world, can generate a step-by-step guide for the robot to follow.
The problem with LLMs, though, is that there’s no way to guarantee that their instructions are possible for the robot to execute. Maybe the person doesn’t have a refrigerator in the kitchen, or the fridge door handle is broken. In these situations, robots need to ask humans for help.
KnowNo makes that possible by combining large language models with statistical tools that quantify confidence levels.
When given an ambiguous instruction like “Put the bowl in the microwave,” KnowNo first generates multiple possible next actions using the language model. Then it creates a confidence score predicting the likelihood that each potential choice is the best one.
The Download: inside the first CRISPR treatment, and smarter robots
The news: A new robot training model, dubbed “KnowNo,” aims to teach robots to ask for our help when orders are unclear. At the same time, it ensures they seek clarification only when necessary, minimizing needless back-and-forth. The result is a smart assistant that tries to make sure it understands what you want without bothering you too much.
Why it matters: While robots can be powerful in many specific scenarios, they are often bad at generalized tasks that require common sense. That’s something large language models could help to fix, because they have a lot of common-sense knowledge baked in. Read the full story.
Medical microrobots that travel inside the body are (still) on their way
The human body is a labyrinth of vessels and tubing, full of barriers that are difficult to break through. That poses a serious hurdle for doctors. Illness is often caused by problems that are hard to visualize and difficult to access. But imagine if we could deploy armies of tiny robots into the body to do the job for us. They could break up hard-to-reach clots, deliver drugs to even the most inaccessible tumors, and even help guide embryos toward implantation.
We’ve been hearing about the use of tiny robots in medicine for years, maybe even decades. And they’re still not here. But experts are adamant that medical microbots are finally coming, and that they could be a game changer for a number of serious diseases. Read the full story.
5 things we didn’t put on our 2024 list of 10 Breakthrough Technologies
We haven’t always been right (RIP, Baxter), but we’ve often been early to spot important areas of progress (we put natural-language processing on our very first list in 2001; today this technology underpins large language models and generative AI tools like ChatGPT).
Every year, our reporters and editors nominate technologies that they think deserve a spot, and we spend weeks debating which ones should make the cut. Here are some of the technologies we didn’t pick this time—and why we’ve left them off, for now.
New drugs for Alzheimer’s disease
Alzmeiher’s patients have long lacked treatment options. Several new drugs have now been proved to slow cognitive decline, albeit modestly, by clearing out harmful plaques in the brain. In July, the FDA approved Leqembi by Eisai and Biogen, and Eli Lilly’s donanemab could soon be next. But the drugs come with serious side effects, including brain swelling and bleeding, which can be fatal in some cases. Plus, they’re hard to administer—patients receive doses via an IV and must receive regular MRIs to check for brain swelling. These drawbacks gave us pause.
Sustainable aviation fuel
Alternative jet fuels made from cooking oil, leftover animal fats, or agricultural waste could reduce emissions from flying. They have been in development for years, and scientists are making steady progress, with several recent demonstration flights. But production and use will need to ramp up significantly for these fuels to make a meaningful climate impact. While they do look promising, there wasn’t a key moment or “breakthrough” that merited a spot for sustainable aviation fuels on this year’s list.
One way to counteract global warming could be to release particles into the stratosphere that reflect the sun’s energy and cool the planet. That idea is highly controversial within the scientific community, but a few researchers and companies have begun exploring whether it’s possible by launching a series of small-scale high-flying tests. One such launch prompted Mexico to ban solar geoengineering experiments earlier this year. It’s not really clear where geoengineering will go from here or whether these early efforts will stall out. Amid that uncertainty, we decided to hold off for now.