Scientists have restored cellular function in 32 pig brains that had been dead for hours, opening up a new avenue in treating brain disease—and shaking our definition of brain death to its core. Announced on Wednesday in the journal Nature, researchers at the Yale University School of Medicine devised a system roughly analogous to a dialysis machine, called BrainEx, that restores circulation and oxygen flow to a dead brain.

The researchers did not kill any animals for the purposes of the experiment; they acquired pig heads from a food processing plant near New Haven, Connecticut, after the pigs had already been killed for their meat. And technically, the pig brains remained dead—by design, the treated brains did not show