The brains of killed pigs have been partly revived hours after death. Here’s everything you need to know about the experiment and what it means for those of us with a human brain.
What happened to the pig brains?
The brains were removed from pigs four hours after they had been decapitated and were then hooked up to an artificial supply of blood-like fluid, in a device called BrainEx, for six hours. Surprisingly, this seemed to reduce the amount of brain cell damage that normally happens after bodily death, and it also seemed to restore brain cells’ ability to perform some functions such as using glucose and oxygen.
Could the dead brains have been aware of what was happening?
The fluid contained drugs that stop nerve cells from firing – partly to help the cells recover, but also to avoid any chance of the brains experiencing some form of awareness. But when some nerve cells were removed and tested separately in a dish without these drugs, they were found to still be capable of sending electrical signals.
Does this mean we can bring people’s brains back to life after they’ve died?
Not at all. There were only limited signs of individual brain cells surviving and functioning – not the coordinated activity of all the brain cells and structures needed to achieve perception or awareness. It would be a massive leap to assume such higher functions are possible. “This is not a living brain, it’s a cellularly active brain,” says Nenad Sestan of Yale School of Medicine, who was part of the team that did the work.
Are we sure the drugs will have blocked any brain activity?
Yes, because Sestan’s team also measured activity of the brains with electroencephalogram (EEG) recording while they were hooked up to the device. There were no brainwaves, which are necessary for any kind of awareness. “The organised electrical activity associated with consciousness was never detected,” says ethicist and team member Stephen Latham of Yale University. If there had been any brainwaves they would have stopped the experiment.
How ethical was this experiment?
The group used pigs that had been killed for food, so caused no extra deaths, and they got approval from all the relevant ethics committees. But some US laws on animal research only concern work done on creatures that are alive, so it’s unclear how they apply to brains in this novel state. The team want the regulations reviewed. To be on the safe side, any such brains should be dosed with a general anaesthetic in future, Nita Farahany of Duke University in North Carolina suggests in an accompanying commentary published in Nature.
How does this change our understanding of the brain?
Until now, we thought that just a few minutes of oxygen deprivation could lead to brain damage, triggering a cascade of irreversible cell death and degeneration. Now we know that at least some cell activities can be restored even four hours after death without any cooling. “Cell death happens across a longer time window than we thought,” says Sestan
Could this affect organ donation after brain death?
Not any time soon. Donor organs usually come from someone who has had a severe brain injury and no longer have a functioning brain stem, a part of the brain that is essential for life. With existing technology, no one recovers after tests have shown brain stem death, says John Dark of Newcastle University, UK.
Are there any other implications?
For a start, the experiment provides a new way to study brains in the lab. And in medicine, the artificial blood substitute could be useful for helping to protect the brain or other organs after damage caused by lack of oxygen, as happens after heart attacks. The fluid contains chemicals that protect nerve cells from damage, and unlike blood, has no immune cells, which may contribute to brain damage. “If this works for brain cells it will also work with some less sensitive organs with some tinkering,” says Latham.
Journal reference: Nature, DOI: 10.1038/s41586-019-1099-1
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