It’s a cliché image from bad science fiction—the living “brain in a jar.” Now scientists at Yale University say they have actually done it.

Pig heads: A team led by Nenad Sestan report in Nature today how they have been picking up severed pig heads from a New Haven slaughterhouse and trying to restore circulation to them a few hours after death.

The experiments were successful in keeping many of the cells inside the brains alive and functioning for more than a day. MIT Technology Review first reported the pig brain experiments in April 2018.

Not conscious: Sestan says while the brain cells lived, the team did not detect organized electrical signaling from neurons. That would have suggested the disembodied brains had regained consciousness.

An ethicist involved in the study said during a conference call with reporters that if there had been evidence of consciousness, the studies would have had to be stopped. Sestan insists the brains are “not alive.”

High-tech jar: The researchers employed a device they built and called BrainEx, which reestablishes circulation of oxygen carrying fluid to the brains, including their small blood vessels, using a series of pumps, filters, and surgical connections.

Death in question: Doctors can declare a person deceased a few minutes after the heart stops—sometimes quickly harvesting the heart and kidneys for others. But this technology could blur the definition of death.

“If technologies similar to BrainEx are improved and developed for use in humans, people who are declared brain dead … could become candidates for brain resuscitation rather than organ donation,” write Stuart Youngner and Insoo Hyun, bioethicists at Case Western University.