This may sound like the plot to a science fiction movie, but this one is firmly grounded in reality. Scientists have managed to implant a human mini brain into the skulls of mice. What’s more, they could check up on how the human cells were doing simply by peering through a little window they inserted in the bone.

The human brain cells were first grown in the lab to form what are called organoids, before being successfully implanted into the brains of mice for the first time ever. Reporting their results in the journal Nature Biotechnology, the researchers describe how the mouse brains even supplied the lentil-sized human cerebrum with a blood supply and nutrients, and that the two tissue types were even communicating.

The team behind the human-mouse brain hybrid first revealed what they had done last year, raising a whole bunch of questions about what this would actually mean. Would it alter the rodent’s intelligence, consciousness, or even identity, for example? In the paper the scientists have addressed some of these concerns, saying that following the implant of the brain tissue, there were no observed differences in the behavior or intelligence of the mice when compared to standard ones.

Researchers have been growing human brain organoids in the lab for a while now, coaxing human stem cells to develop into structures that resemble developing human brains, but the size of these has been restricted as the cells cannot get enough nutrients. Recently, however, one team has managed to get their mini-brains to grow their own blood vessels, which will hopefully allow them to get over this issue and grow the brains into larger organoids.

But this latest study has taken the smaller organoids and implanted them into over 200 mouse brains. Around 80 percent of these took, and within 14 days they had already developed a complex network of vessels, sent out axons to surrounding mouse brain tissue, and were even firing in sync with the natural mouse brains, showing quite clearly that the two tissues were communicating.

This research – despite sounding fairly extreme – could have some really significant applications. One of the main reasons for testing the viability of inserting small bits of brain into the heads of mice is that one day they could be used as brain repair kits.

The scientists envision using these little pieces of cortex to patch up human brains that have been damaged or injured, hopefully helping to restore function. Obviously, that is likely to be a long way off, but this work is an incredible starting point that lays down some of the basics and provides proof of concept if nothing else.