Scientists are to announce they have successfully grown human brain organoids inside the brains of lab rats and mice.

First reported by STAT, the research will be presented at the annual meeting of the Society for Neuroscience this weekend in Washington DC.

Organoids are small clumps of cells that are basically miniaturized versions of larger organs. Previous research has shown that stem cells can be used to grow them.

In this latest research, scientists inserted organoids into rat brains and connected them to blood vessels. They found that some organoids actually grew physical links with these brains.

The organoids survived for quite a long period of time, up to two months in one case, and were able to not only transfer blood but also nerve signals.

“We are entering totally new ground here,” Christof Koch, president of the Allen Institute for Brain Science in Seattle, told STAT. “The science is advancing so rapidly, the ethics can’t keep up.”

The mini brains don’t quite behave like a real brain, but they do suggest that functional human tissue can develop within a rodent. That they can also connect to blood vessels suggests they can be given a blood supply.

There are, of course, ethical implications. Human stem cells currently aren't allowed to be put into the embryos of vertebrates, but it’s fair game when it comes to organoids.

These cannot grow to the same size as human brains, but it does raise questions about growing something human-like in an animal, an ethical area that’s only now really being explored. We don't know what it might do to their intelligence, consciousness, or even species identity.

Organoids are usually grown in a dish, but putting them in an animal gives us a better idea of how they behave. They could be used to help test various drugs and diseases.

“It’s also a chance to peer further into the murky depths of consciousness itself,” notes Discover magazine.

“A rat-human hybrid would certainly blur the line between human and animal consciousness, bringing us that much closer to figuring out what it is that makes us human.”