On March 28th, in a National Institutes of Health meeting on ethics in US neuroscience, Yale Neuroscience Professor Nenad Sestan announced that by experimenting on 100 to 200 brains of decapitated pigs from slaughterhouses, he could keep the organs alive using heaters and pumps to circulate the brains with artificial blood. Billions of cells were discovered to be healthy and capable of working as normal, despite decapitation. This is the first reported success in separating live brains from the bodies of large mammals without using cooling.
Sestan proposed that the brains may be used as models for treatment of diseases such as cancer and Alzheimer’s disease to inform on therapy for humans, since we need models with large amounts of intact brain to see the full effect of treatments. The research was initially funded to help to produce an atlas of the brain, as the connections of the brain are not yet well understood. 17 neuroscientists and bioethicists, including Sestan, published a Nature article in April 2018 proposing methods that may ensure that human brain tissue harvested using these techniques is not conscious during experimentation (experimenting on live human brain tissue is ethically complex as it is potentially conscious, making testing and termination of samples problematic). Suggestions included producing small amounts of nervous tissue known as organoids lacking capability for consciousness, preserving living human brain tissue removed in surgery and inserting human brain tissue into mice.
The immediate media response to the news was the possibility of using method in human brain transplant to keep the tissue alive between bodies. Since live brain maintenance has only been done in pigs, we cannot assume it can be done in humans, but Sestan claims that the techniques could apply to other organisms. In 1970 a successful head transplant between rhesus monkeys by Robert White produced a recipient that survived for 8 days, yet the method was discarded as connection of the spinal cords was not possible. Italian neurosurgeon Sergio Canavero announced in November 2017 that his colleague Xiaoping Ren had transplanted of the head of one human cadaver to another, as a ‘rehearsal’ for live human head transplant. Canavero and Ren have previously experimented with transplantation of live rat, mouse, dog and primate heads. Canavero and Ren predicted their first attempt at live human head transplant to be in late 2017, yet have now changed their estimate to ‘imminent’. Canavero has also alleged that he knows a method to connect the spinal cords.
However, Canavero and Ren have only managed to do human head transplants on cadavers and live head transplants on animals, so cannot claim that they are capable of performing live human head transplants. Arthur Caplan, head of ethics in the New York University medical school, does not believe that Canavero will ever receive the ethical go-ahead, and suggests that Canavero is conducting research in China as the ethics laws are more relaxed than those of the US and Europe. Professor Sestan mentions that there is no evidence that the pig brains may regain consciousness if transplanted into another pig and has claimed no intention of using this technology to test brain transplantation. Tests suggested that the brains were not conscious, although this negative result may be due to chemicals used to prevent swelling preventing neuronal signals. Steve Hyman, director of psychiatric research at the Cambridge, Massachusetts Broad Institute has said that brain transplants are “not remotely possible”, as he is critical of the idea that we could treat the brain in the same way that we treat organs that are routinely transplanted.
Professor Sestan has refused to comment on his findings as the research is yet to be published, and he had not wished for the news to become public prior to publishing. This means that we do not know if the research will stand up to the rigorous scrutiny of a journal’s peer review. If the experiments are accepted, however, it seems that we may be conducting research on full pig brains in the future, mapping brain cell connections and testing drugs and therapies for human brains in pig brains. Testing on human brains brings up concerns including consent, the definition of death and ownership of living human brains, but using pig brains to inform us about human disease avoids these issues for the most part, so long as unnecessary suffering is not inflicted upon the animal. As for the use of these pig brains in studying human head transplants, historical experiments show that head transplants are possible in a number of animals, but even if brain transplants to lengthen life in humans becomes possible they will not be an option any time soon, due to a huge range of ethical concerns, a lack of evidence of consciousness and loss of spinal cord connection.