NQUIRY: AN OCCASIONAL COLUMN
The Future of Brain Transplants
- By Peter Tyson
- Posted 08.26.10
- NOVA scienceNOW
Will we ever grow replacement brains or do whole-brain transplants?
Need a new body part? Tissue engineers are now growing human bladders, lungs, and other organs in the lab with the hope that, someday soon, such organs may replace diseased organs in people. Transplant surgeons, for their part, routinely place donated kidneys, hearts, and other organs into patients whose own organs are failing. They have transplanted hands, arms, even, famously, a face.
This has left me wondering, where does the brain come into all this? Will we someday grow replacement brains or do whole-brain transplants? Three questions leap to mind: Why would we? Could we? And should we?
On bad days, we may feel we'd like a brain transplant, but what are the prospects realistically? Some experts have actually put their minds to it.
EnlargePhoto credit: © Henrik Jonsson/iStockphoto
I must admit to feeling a bit squeamish with the whole idea, which you might agree has a sizeable "yuck" factor. And I felt a little sheepish when I called experts to ask them about it. Would they dismiss me out of hand, beseeching me not to waste their time with a subject best left to science-fiction writers? But with science and medicine advancing at a dizzying pace, and with questionable medical procedures of the past as cautionary tales, it seemed like a subject worth addressing, if only perhaps to reject it as untenable, unconscionable, or simply too ghastly to contemplate.
WHY WOULD WE?
First of all, why? What medical justification could exist for growing a new brain, or part of one, and placing it in someone whose own brain, or part of it, was removed?
"Certainly there are situations where people have tumors and have to have areas resected or situations where people are brain-dead," says Doris Taylor, whose tissue-engineering lab at the University of Minnesota's Stem Cell Institute is experimenting with growing entire replacement organs, including 70 livers last year alone. "Certainly there are situations where somebody has an accident that leaves their brain stem injured. Would it be nice to be able to regrow the appropriate regions? Absolutely. Talk to any paraplegic or quadriplegic out there. They would love to have new cervical neurons or brain-stem regions."
Other researchers echoed Taylor's sentiments—that the future of brain tissue engineering likely concerns small pieces, not the whole enchilada.
Trying to make or reestablish tiny connections in the brain, even between single neurons, is closer to reality than growing whole brains, tissue engineers say.
EnlargePhoto credit: © Sebastian Kualitzki/iStockphoto
"We're not going to make whole brains in a dish and then just transplant them," says Evan Snyder, head of Stem Cells and Regenerative Biology at the Sanford-Burnham Medical Research Institute in California. "But what people are playing with is, is it possible to do little bits of tissue engineering in a dish and then put these tissues into small areas [of the body] and see whether you can make some connections?" Perhaps help a patient with Parkinson's disease regain some lost neural functionality, say, or buy a quadriplegic another segment of spinal cord function such that she can breath a little better on her own or can now move her thumbs—that's the hope, Snyder says.
"Building a whole brain? That's kind of out there."
What about transplanting existing brains from one individual to another, like we do with donated hearts or kidneys? Under what scenario would we consider that? About a decade ago, Dr. Robert White, a neurosurgeon at Case Western Reserve University, received a burst of media attention by advocating what he called "whole-body transplants" for quadriplegics. (Because the brain can't function without the head's wiring and plumbing, White noted, a brain transplant, at least initially, would be a head transplant. And, perhaps because of the yuck factor, he preferred to call such an operation a whole-body transplant.)
Quadriplegics often die prematurely of multiple-organ failure, White said. If surgeons could transfer the healthy body of a donor, such as a brain-dead individual or someone who has just died of a brain disease, to the healthy head of a quadriplegic, they could prolong that patient's life. Brain-dead patients already serve as multiple-organ donors, so a whole-body transplant is not as macabre as it might at first sound, White argued.
Could surgeons detach a living human head (brain included) and place it on the living body of a donor? Robert White says it’s possible—and may be in our future.
EnlargePhoto credit: © Luis Carlos Torres/iStockphoto
I tracked down Dr. White, who is now retired after 60 years as a brain surgeon but is still active as a writer and consultant. "I think this is an operation of the future," he told me on the phone. "But it is certainly out there, and under these circumstances [of quadriplegia], the concept of giving somebody who is important or quite young a new body is not beyond comprehension." And it should be discussed now, White feels, because it may well be coming. "We're still within just the first 100 years of transplantation," he said. "Who knows where we'll be after another 100 years?"
COULD WE GROW NEW BRAINS?
Let's say for the sake of argument that we had sound medical reasons for doing such procedures. Could we, technically speaking? Could we grow a whole human brain, or even part of one, in a laboratory?
"There is now data showing that if you put stem cells in an area of brain injury that the cells actually home into the injured brain area, and they can take up residence there and exhibit some sort of functionality," says Tony Atala, director of the Wake Forest Institute for Regenerative Medicine and head of one of the premier tissue-engineering labs in the country. "But building a whole brain? That's kind of out there." How about a single lobe? "That would be extremely complex to do," he said. "As a scientist, you never say never, because you never know what will be within the realm of possibility several centuries from now. But certainly to replace a lobe today, that would be science fiction with current technology."
Doris Taylor was more willing to speculate but was also cautious. "We can decellularize the brain," she told me, referring to her lab's technique to chemically strip all cells from donor organs, leaving a kind of cell-less scaffold that can be seeded with stem cells and "regrown." "But whether it's possible to restore brain cells appropriately, who knows?" She paused. "And in the case of the brain, how would you know? There's such a wide spectrum of behavior and functioning. I'm not sure we'd ever have an end point to know how to measure." She paused again. "I have no doubt that we can rebuild at least some neural pathways. The question is, will that rebuild a brain, including everything you need for mind-brain function, or even a piece thereof? I really don't know."
Taylor envisions more modest steps forward, such as rebuilding small parts of the brain to decrease the size or frequency of seizures in an epileptic or to help restore some functionality in a stroke victim who had suffered severe neurologic loss. "I could imagine considering growing regions of brains to graft in," she says. "But are we within five to ten years of that? That's hard to imagine."
While the focus of intensive research, successfully reconnecting the spinal cord to the brain following a serious spinal injury remains beyond current science.
EnlargePhoto credit: © Mads Abildgaard/iStockphoto
Research with neural stem cells has shown that it's extremely hard to make even the simplest neuronal connections, much less regenerate neurons, as had been hoped early on. "The vision of the stem cell field 20 years ago was you have a patient in a wheelchair and you stick a stem cell into his brain or spinal cord, and he'll come bounding out of his wheelchair and run the Boston Marathon," Snyder says. "We know now that's not the way it's going to happen."
COULD WE TRANSPLANT EXISTING BRAINS?
What about a head transplant—or, if you prefer, a whole-body transplant? Doable? White thinks it is, even as he acknowledges that the financial costs would be prohibitive.
"Could you keep an isolated human head alive? That's creepy. Very creepy."
"I've had plenty of time to think about it, and the operation itself, although complex, really involves structures in and about the neck," White told me. "You're not cutting into the brain, and you're not cutting into the body, just severing everything at the neck. It's a very complex operation, because you have to make sure that the body's kept alive and the head's kept alive. But this has all been worked out in smaller animals."
Forty years ago, in studies that to some commentators smacked of Dr. Frankenstein, White and his team experimented with transplanting the newly detached head of a live rhesus monkey onto the body of another monkey that had just had its head removed. The longest-lived such hybrid, which reportedly showed unmistakable signs of consciousness, lasted eight days.
All the surgery involved in a head transplant would take place in and around the neck, White says. While mind-numbingly complex, such an operation is conceivable, he argues.
EnlargePhoto credit: © Max Delson Martins Santos/iStockphoto
"With the significant improvements in surgical techniques and postoperative management since then," White wrote in a 1999 Scientific American article, "it is now possible to consider adapting the head-transplant technique to humans." White acknowledges that a quadriplegic who got a new body today would remain paralyzed below the neck, because successfully reconnecting the brain to the spinal column remains beyond our reach.
"That's a very interesting scenario," Taylor said when I brought up White's idea. But would it work? "Well, technically, people can do almost anything," she said. "You can sew something the size of or smaller than a human hair, so technically I could imagine that working. But there are huge things we still don't know and have to learn. That doesn't mean that I can't imagine doing all of this. It does mean that I'm going to ask some difficult questions before I say it's ready for prime time or even clinical utility."
Snyder was also willing to consider possibilities, though for him the yuck factor loomed large. The first step, he felt, would have to be the ability to sustain a head independent of a body, even for a short period. "Could you keep an isolated human head alive such that it's thinking and talking and all we need to do is perfuse it with the right chemicals and the right nutrients and keep the acid-base balance fine?" he said. "That's creepy. Very creepy." Agreed, but how soon? "I can't say it's absolutely impossible," he said. "But I don't see that happening in the next 100 years."
SHOULD WE TRANSPLANT EXISTING BRAINS?
One expert who has given a lot of thought to the notion of head transplants—and was not a bit hesitant to talk about them—is Paul Root Wolpe, a bioethicist at the Emory Center for Ethics at Emory University. (In fact, he once debated White on the subject on radio.)
"I'm always wary of the valuable-people argument," says Paul Root Wolpe, about the idea of singling out individuals for life-prolonging head transplants because of their "importance."
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Wolpe has several problems with the concept, he told me. One concerns use of resources. Referring to a putative head transplant, he said, "The desperate attempt to keep individuals alive using more and more resources seems to me to be extraordinarily misguided when you're talking about a world where people are dying for lack of resources, very preventable kinds of diseases and issues like malnutrition." The idea that it could prolong the life of someone deemed important did not sit well with him. "I'm always wary of the valuable-people argument—'Forget keeping not-valuable people alive, that's kind of a waste, but what if we could keep valuable people alive?' I have a lot of trouble when I put the argument that way." Wolpe would consider a whole-body transplant, he says, "a fundamental ethical transgression."
Another concerns a person's bodily integrity. "You are talking about a fundamental kind of change whereby a body becomes simply a means of supporting a head, where your sense of what it means to be a whole human being has been compromised in a very new way," he says. Wolpe believes this change to be intrinsically different than that brought about by heart transplants, which, when such operations first started taking place, did raise a host of questions in people's minds about what it would mean for a recipient's sense of wholeness.
"Who do we grow a new brain for? I'm not sure of the medical problem that that solves."
One's very sense of selfhood would be at stake, Wolpe argues. In the West we tend to think of the brain as the locus of self, but culturally that is a very new idea, and it's still not shared in many cultures, he says. Consider Japan, where the locus of self is thoracic and abdominal. "That's why when you commit seppuku you disembowel yourself, you don't cut your head off, because you're attacking yourself at the seat of selfhood," he told me.
The notion that if you put his head on someone else's body that the resulting individual would be him and not the other person simply because the hybrid had his brain is, Wolpe says, "theory not fact, a philosophical position rather than a scientific reality. What you may end up finding is that when you transfer a brain from one body to another, the resulting organism is not solely what one would think of as the person whose brain it was but also has enormous components of the person into whose body it goes."
Altogether, the ethical issues surrounding head transplantation are insurmountable, Wolpe feels.
"Don't go there" would seem to be the position of most experts when it comes to contemplating the transplantation of human brains, either nature- or lab-born.
EnlargePhoto credit: © ktsimage/iStockphoto
SHOULD WE GROW NEW BRAINS?
As for growing brains, Wolpe has a hard time seeing how you could justify it medically. "Who do we grow a new brain for? Do we grow it for someone with Alzheimer's? Do we grow it for someone with a severe brain tumor?" I didn't need to ask him to speculate. "Say you had a severe brain tumor, and I took a stem cell from you and I grew a new brain for you and got rid of your old brain and put in your new brain, none of you would be there. Your memories, your ideas, your thoughts, your thinking of your wife as your wife and your kids as your kids—it's all gone, unless we can also transfer all your memories, thoughts, and ideas to a new brain.
"So I'm not even sure what a brain transplant means in that context," he continued. "It means wiping the slate clean and now having a pre-birth-level brain in a 60-year-old person or whatever? I'm not sure of the medical problem that that solves."
A LOAD OFF
Wouldn't, couldn't, shouldn't—that seems to be the general consensus for both growing and transplanting human brains, at least for the forseeable future. That's a relief—my head hurts just thinking about them.
