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The ability of neuroscientists to create, grow and use human brain tissue in the lab is moving fast. So fast in fact that the journal Nature this week published a commentary signed by 17 neuroscientists, biologists and ethicists calling for an ethical framework for this endeavour.

The authors outline the three variants of such brain tissue: organoids, known as 3D or 鈥渂rain balls鈥�, which are structures grown in the lab from pluripotent stem cells; ex vivo brain tissues, which are those removed from humans and kept alive; and chimeras, or human-animal hybrids, in which human cells are transplanted into the brains of animals.

The authors make clear that despite the fact that none of these currently has human capabilities such as feeling pleasure, pain or distress, the possibility is becoming less remote.

Organoids have proven investigating how diseases like Alzheimer鈥檚 and Zika work within the human brain. They are also, by all accounts, astonishing 鈥� the mini-brains can respond to external stimulus, .

Meanwhile, chimeras are possibly the human brain surrogate. Deep ethical concerns about them have been growing recently. In 2017 that tiny human brain pieces had been implanted into rats and mice, raising the hackles of bioethicists who worried that it could be possible for human-like brain tissue to mature in rodents. According to the call for ethical discussions in Nature, it turned out that such mice 鈥減erformed better at certain tasks involving learning鈥�.

Separately, another group of that their growing their own vessels to connect to a blood supply.

Case by case

How risky are these experiments? And even if the possibility of a non-human animal or organoid being sentient in a human way is remote, shouldn鈥檛 we decide where to draw some lines? How many human cells in an animal is too many? Are there even limits?

For example, the authors cite one experiment where pig embryos were injected with human stem cells. When the fetuses were terminated in the first trimester, more than 150 embryos had become chimeras, where 1 in 10,000 cells in what would become hearts and livers were human. Despite there being no chance that any of those animals would develop human features or feelings, some people become understandably unnerved when they hear about this. So the authors recommend ethicists and the public discuss what kind of lines should exist to regulate these experiments, and where to draw them.

There have been previous efforts to discuss the ethics of neurological research, however, the authors believe more should be done. I agree, and I also believe that in addition to ethicists, scientists themselves should make their voices heard. To create meaningful ethical boundaries that advance health technologies, we must fully understand why this sometimes unsettling science is valuable.

I also believe it is useful to learn from existing law; human embryos enjoy a special legal status, and we can consider that human brain tissue might as well.

Donors of aborted fetal tissue, or unused embryos, understand that the tissue they contribute will be used along the lines of a tried and true regulatory and ethical framework. So, do people have a right to know what kind of research the brain tissue that they or their loved ones donate is being used for? The authors believe that for now, those decisions should 鈥渂e made on a case-by-case basis鈥�.

Communication is crucial

But we need a place to begin to conceptualise what an ethical framework looks like. Bioethicist David DeGrazia鈥檚can be useful here.

While it can be controversial to say so, most people believe that compared with a human, a sheep has a lower moral status, towards which we have different moral obligations. Does a sheep with human brain tissue create a different level of moral status, or personhood, higher than a sheep, but lower than a human? Perhaps it does, and perhaps this can be a way forward for considering how brain surrogate research progresses.

Because there is no doubt about it, the research must advance 鈥� but in a way that begins to create an appropriate ethical framework. Open communication between scientists, ethicists and the public is crucial now, before human brain surrogates astonish us in more worrying ways.