As medical and scientific technologies push forward, the line between life and death becomes more and more blurred. Death is widely defined as the moment when the biological functions of a living creature cease, but we’ve seen many examples of scientific measures that can string a dying body along bizarre ways. Transplanting a head — as one Italian surgeon claims to have done — or preserving the function of a brain outside of its body can make us question what death really is. A team of researchers from Yale says they’ve done just that, keeping the brain of a pig alive, outside of its body, for up to 36 hours after the body itself “died.”

The researchers, who say they used over 100 pigs that were in the process of being slaughtered, claim to have revived the brain of pigs that had been “dead” for as long as four hours. They took the decapitated heads and used a technique known as BrainEx to restore circulation to the tissue and bring the brains at least partway back to life.

There’s a big “but” in this story, which is that the brains themselves showed no measurable signs of activity in terms of brain waves. However, the researchers were able to determine that “billions” of the cells in the brains were healthy and alive after the procedure. But healthy brain tissue isn’t an indication that the animal’s consciousness was still salvageable, and by all accounts it seems that the brain being technically “alive” didn’t mean the animal wasn’t still dead.

“These brains may be damaged, but if the cells are alive, it’s a living organ,” Steve Hyman, of the Broad Institute in Cambridge, told MIT Technology Review. “It’s at the extreme of technical know-how, but not that different from preserving a kidney.”

The research is obviously very interesting, but it also raises some pretty serious ethical questions, especially when imagining the same kind of technology being used on a human subject. Could we reach a point where our brains could simply be placed into new bodies, or exist on their own? And if so, would our consciousness survive such a procedure? Hyman says such a thing “is not remotely possible,” at least not yet.