The brains of dead pigs have been restarted by scientists in an experiment which raises serious ethical and philosophical questions about what it means to be alive and the prospect of bringing people back from the dead.
Researchers at Yale University pumped a cocktail of chemicals into the brains of 32 pigs which had been slaughtered in a nearby abattoir four hours earlier and their heads decapitated.
Although the ‘zombie’ animals never regained consciousness, many basic cellular functions including blood circulation and metabolism switched back on for ten hours, ending long-held assumptions that brain death is irreversible.
Experts have raised concerns that the tests may open the door for unscrupulous cryogenic companies to attempt to reanimate people who had their bodies frozen after death, or even retrieve memories or images from the brains of the dead.
There are also fears that the animals did not regain consciousness only because the life-giving soup of chemicals included drugs to limit the activity of brain cells.
In fact, the scientists involved in research were so concerned that the pigs would 'wake up’ that they had anaesthesia and freezing equipment on hand to quell perception if it arose.
Co-author Stephen Latham, director of Yale’s Interdisciplinary Centre for Bioethics, said: “Restoration of consciousness was never a goal of this research. I want to make clear that consciousness was never detected.
“It was in fact a concern of the researchers that consciousness might be induced and they were prepared to intervene with the use of anesthetics and temperature-reduction to stop organised global electrical activity if it were to emerge.”
First author Dr Zvonimir Vrselja added: “At no point did we observe the kind of organised electrical activity associated with perception, awareness, or consciousness.
“Clinically defined, this is not a living brain, but it is a cellularly active brain.”
The death of brain cells and awareness was previously thought to be a swift process, occurring within seconds or minutes of oxygen and blood supply being cut off.
Without fuel, energy stores in neurons vanish within minutes triggering a cascade of death and injury molecules which cause irreversible degeneration.
But in recent years the Yale team had noticed that small tissue samples they were working on in the lab still showed signs of life even hours after death. The pig brain experiments were an attempt to find out just how widespread that activity was.
They used a special machine called ‘BrainEx’ which pumps a solution mimicking oxygenated blood into the brain. It also included chemicals to protect nerve cells.
Senior author Nenad Sestan, Professor of Neuroscience, Comparative medicine, Genetics, and Psychiatry at Yale, said the new study shows a "previously underappreciated capacity for restoration of circulation and certain molecular and cellular activities multiple hours after circulatory arrest".
But Nita Farahan, Professor of Law and Philosophy at Duke University, said groups like The Royal Society and Nuffield Council on Bioethics needed to set ethical principles for future research.
“The discovery that mammalian brains can be made to seem ‘slightly alive’, hours after the animals had been killed, has implications that ethicists, regulators and society more broadly must now think through,” he wrote in the journal Nature.
“It opens up possibilities that were previously unthinkable. Hundreds of people worldwide have already paid to have their brains frozen and stored, in the hope that scientists will one day be able to revive them. It’s easy to imagine misapplications of brain perfusion following the publication of the 'BrainEx' study alone.
“Another question is what information, if any, could plausibly be retrieved from the brain. Various groups are developing ways to decode the neural activity of living people, for instance to probe their memories or the images they have seen in their dreams. Could such approaches one day be applied to brains after death?”
Experts said guidelines were also needed to make sure that animals used in experiments did not end up in a "grey area - not alive, but not completely dead".
Although there is no immediate clinical application for ‘BrainEx’, the life-giving therapy could one day help salvage brain function in stroke patients.
Commenting on the research Dominic Wilkinson, Professor of Medical Ethics at Oxford University, said: “After someone dies, their brain normally deteriorates and disintegrates within a matter of hours.
"This intriguing research demonstrated in pigs that it was possible to halt the progressive cellular damage that normally occurs in the tissue of the brain after death.
“This research reminds us that ‘death’ is less an event, and more of a process that occurs over time. Cells within the human organism may be alive for some period of time after the human person has died.
“If, in the future, it was possible to restore the function of the brain after death, to bring back someone’s mind and personality, that would, of course, have important implications for our definitions of death.”
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