US scientists have partially revived pig brains four hours after the animals were slaughtered. The scientists who carried out the experiment* at Yale University are hopeful that it will provide a new way of researching diseases like Alzheimer's. Although the experiments stopped short of restoring consciousness they raise questions about the nature of death itself and the ethics of "reviving" animals for research.
The study showed the death of brain cells could be halted and that some synapses were restored. However, there were no signals from the brain that would indicate awareness or consciousness but the findings challenge the idea that the brain goes into irreversible decline within minutes of the blood supply being cut off.
Writing in the journal Nature the authors collected 32 pig brains from an abattoir. Four hours later the organs were connected to a system made by the team at Yale University that pumped a liquid containing synthetic blood to carry oxygen and drugs to slow or reverse the death of brain cells. The pig brains were given the restorative cocktail for six hours.
The technique restored some crucial functions, such as the ability of cells to produce energy and remove waste, and helped to maintain the brains’ internal structures. The brains also showed a normal response to medication and used up the same amount of oxygen as a normal brain - all this 10 hours after the pigs were decapitated.
Crucially there was no sign of the brain-wide electrical activity in an electroencephalogram that would signal awareness or perception.
The research transforms ideas about how the brain dies, which many thought happened quickly and irreversibly without a supply of oxygen.
Professor Nenad Sestan, a professor of neuroscience at Yale University, said: "Cell death in the brain occurs across a longer time window that we previously thought.
"What we are showing is the process of cell death is a gradual, stepwise process.
"And that some of those processes can be either postponed, preserved or even reversed."
The pig brains came from the pork industry; the animals were not raised in a lab for this experiment. But the Yale scientists were so concerned the pigs might become conscious that they gave drugs to the disembodied brains to reduce any brain activity. And the team were constantly monitoring the brains to see if there was any sign of higher brain functions. In that case they would have used anaesthetic and ended the experiment.
Ethicists, writing in Nature, say new guidelines are needed for this field because animals used for research could end up in a "grey area - not alive, but not completely dead".
The immediate benefit of this work will be for scientists studying the brain in diseases like Alzheimer's which will allow them to explore the full three-dimensional connectivity of the brain which cannot be done with post mortem sections of brain. In the long-term, scientists hope to find better ways of protecting the brain after traumas such as a stroke or being starved of oxygen at birth.
Dr Andrea Beckel-Mitchener, from the Brain Initiative at the US National Institute of Mental Health, told the BBC: "This line of research could lead to a whole new way of studying the post-mortem brain.
"It also could stimulate research to develop interventions that promote brain recovery after loss of brain blood flow."
However, the researchers say it is still far too early for the field to make a difference to patients after injury.
Professor Sestan said: "We don't yet have knowledge whether we would be able to restore normal brain function."
Does this change the meaning of death?
At the moment no, but some ethicists say we should have the debate now as people who are "brain dead" are a major source of organs for transplant.
Professor Dominic Wilkinson, a professor of medical ethics and a consultant neonatologist in Oxford, told the BBC: "Once someone has been diagnosed as 'brain dead' there is currently no way for that person to ever recover.
"The human person that they were has gone forever.
"If, in the future, it were 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."
*Vrselja Z, Daniele SG, Silbereis J, et al.Restoration of brain circulation and cellular functions hours post-mortem. Naturevolume 568, pages 336–343 (2019), 17 April 2019.