“Most fundamentally,” write a team of leading researchers in an accompanying editorial in Nature, “it throws into question long-standing assumptions about what makes an animal – or a human – alive.” Illustration: Matt Golding Credit: The brain chamber Our brains need huge flows of blood and oxygen to keep them alive. Just a few seconds of interrupted blood flow is enough to cause irreversible brain damage, scientists have long believed. This finding upends that.

At Yale, a team of researchers led by neuroscientist Nenad Sestan built a machine that can pump blood, oxygen, and chemicals that prevent cell death into a 'brain chamber' that carefully controls temperature and humidity. They call it BrainEx. The team strapped pigs' brains – sourced from abattoirs via ice-filled biohazard boxes – into their machine more than four hours after the animals had been killed. And the brains – they tested 32 in total – appeared to come back to a form of life. Blood started flowing through veins and into cells. The cells started to breathe in oxygen and consume sugar, and started to regulate their own salt levels. Loading Replay Replay video Play video Play video Most importantly, the machine seemed to stop the brains degrading. On scans and under the microscope, the cells in crucial parts of the brains appeared intact. Some even spontaneously sparked electrical charges – the basis of how a brain works.

"It’s frankensteinish – we have taken dead bits and brought them back to life," says Dr Steve Kassem, a neuroscientist at NeuRA in Sydney. “The neurons are on, working, functioning. Think of it sort of like the factory is on and working, but we don’t know if it’s producing anything.” The brains' overall electrical activity – the sparks in the lobes that signify consciousness – did not restart in the six hours it sat in the chamber. Had it, the researchers were ready to administer an anaesthetic and cool the brain back to oblivion, which raises another question: what are the ethics of killing a pig twice? Other experiments have shown that consciousness might be able to restart if the brain is kept in the chamber for long enough. Or it could be the brain needs an electrical shock to restart thought patterns.

Regardless, a conscious brain could well be possible. Big questions, big problems Before that next step can be taken, scientists from around the world will need to debate how to do it ethically. “If you then revive the tissue, we don’t know for certain that some level of awareness might return. That’s the major ethical implication in this work,” says Ashley Bush, a professor of neuroscience at the Florey Institute. “You couldn’t imagine a worse nightmare than to be brought back to life after death but to be severed from your body. They are very alert to that possibility. We have to be very careful.”

Dr Kassem agrees. "Put someone in a sensory deprivation tank for 10 minutes and they start to lose their mind – let alone forever." The dead pigs' brains started to function but showed no sign of consciousness.