It emerged that scientists are integrating clusters of human brain cells into rodent brains in a bid to treat a number of illnesses from Alzheimers to Zika. The respected MIT Technology Review reported researchers have used contoversial stem cell techniques to grow tiny clumps of human brain called organoids. These organoids have been almost routinely inserted into rat brains and connected to a blood supply – effectively transplanting the brain of the donor human into a rat. In a scenario straight out of a horror movie some of these organoids have then grown physical connections with the host rat brain – creating a human-rat mutant.

Getty Mouse-brain: But human brain parts called organoids are being transplanted into rodents

DX Rat-like cunning? Human brain organoids have been transplanted into rodents

A further report in science journal Stat says: “Some of the axons grew as much as 1.5 millimeters, connecting to the corpus callosum, a bundle of neurons connecting the left and right cerebral hemispheres. “When the scientists shined light on a rat’s eye, or stimulated brain regions involved in vision, neurons in the implanted organoid fired. “That suggested the human brain tissue had become functionally integrated with the rat’s.” The success of these experiments, and the prospect of more and bigger human brain cells being transplanted to bigger animals has led to a mass of ethical questions – not least do the organoids have consciousness? And when does a rat stop being a rat and start being a human?

Getty Brain drain: Rats have long been used for brain research

Stanford bioethicist Hank Greely said: “People are talking about connecting three or four but what if you could connect 1,000? “That would be getting close to the number of cells in a mouse brain. “At some future point it could be that what you’ve built is entitled to some kind of respect.” The situation is so acute that at least one laboratory - the joint Havard-MIT George Church synthetic biology lab - employs a full-time bioethicist.

Getty Coke and a smile? This rat was part of US research onto the effects of cocaine