Researchers at Yale University have restored circulation to the brains of decapitated pigs, and kept the organs alive for several hours.
Their aim is to develop a way of studying intact human brains in the lab for medical research.
Although there is no evidence that the animals were aware, there is concern that some degree of consciousness might have remained.
Details of the study were presented at a brain science ethics meeting held at the National Institutes of Health (NIH) in Bethesda in Maryland on 28 March.
The research has also been reported on this week in the MIT Technology Review.
The work, by Prof Nenad Sestan of Yale University, was discussed as part of an NIH investigation of ethical issues arising from neuroscience research in the US.
Prof Sestan explained that he and his team experimented on more than 100 pig brains.
They discovered that he could restore their circulation using a system of pumps, heaters, and bags of artificial blood.
As a result the researchers were reportedly able to keep the cells in the brain alive and capable of normal activity for as long as 36 hours.
Prof Sestan is said to have described the result as "mind-boggling". If this could be repeated with human brains, researchers would be able to use them to test out new treatments for neurological disorders.
But Prof Sestan is among the first to raise potential ethical concerns. These include whether such brains have any consciousness and if so deserve special protection, or whether their technique could or should be used by individuals to extend their lifespans - by transplanting their brains when their bodies wear out.