Three weeks ago, a Yale University neuroscientist, Nenad Sestan, explored the ethical implications of experiments using human brain tissue in an essay in the journal Nature. Then last week Sestan's own brain research was splashed across tabloids under lurid headlines like "Yale experiment to reanimate dead brains promises 'living hell' for humans."

First, a reality check: Sestan’s research used pig brains, not human ones, and nothing was reanimated. Bringing a dead brain back to life remains squarely in the realm of science fiction. But what Sestan and his team accomplished does take science into uncharted waters. Brain research is advancing so quickly that ethicists are scrambling to keep up.

The Yale researchers collected brains from 200 pigs at a local slaughterhouse and rushed them back to their lab, where the organs were kept medically active (though not conscious) by a system of pumps, heaters and oxygen-carrying fluid. The system is known officially as BrainEx and unofficially as “brain in a bucket.”

Sestan declined to speak with MACH about the experiment, pending the publication of results in a scientific journal. Most of what we know about his work comes from news reports of a recent workshop on brain science and ethics convened in Bethesda, Maryland, by the National Institutes of Health.

But Sestan’s work, which he described at the meeting, is being widely discussed and debated by other attendees, including Anna Devor, head of a brain-imaging lab at the University of California, San Diego.

Devor is excited about what Sestan’s research might mean for the treatment of strokes and heart attacks. “There’s a very low survival rate for cardiac arrest, partly because we know so little about what’s best for the brain after blood flow stops for a while,” she says, adding that decapitation in a slaughterhouse is a weirdly useful analog of what happens when the heart stops pumping.

BrainEx shows that it is possible to keep brains alive, both for lab research and, potentially, for human medical therapy. “This result also shows the gray area around the idea of ‘brain death,'” Devor says, and could perhaps someday be used to pull patients back from the shadows. “The hope is that we can transition people in a coma back into a state where the brain is active,” she says.

Human brains in mouse skulls

Just as the BrainEx news was spreading, a group led by Fred Gage at the Salk Institute for Biological Studies in La Jolla, California, announced that they had performed another feat of neural engineering. Whereas Sestan is finding ways to keep brains alive, Gage’s team is growing new brains — using human cells.

The Salk team introduced clumps of human brain tissue inside the brains of lab mice, and got these “organoids” to diversify and develop a network of connections. Previously, brain organoids were grown in test tubes or lab dishes that severely limited their growth. Implanting them into an animal host raises the scientific and ethical stakes.