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What it will take for a head transplant to work

 

In 1970, a team of neurosurgeons pulled off a feat that was every bit as remarkable as it was controversial. Led by the renowned Robert J. White, they removed the head of a living rhesus monkey and hours later reattached it to a separate body. Though paralyzed, the donor body supplied enough blood to the brain to allow the monkey to consciously smell, hear, taste and see for a few days before the body’s immune system rejected the transplant.

White, who passed away in 2010, was never able to advance the procedure to where it can be performed on humans, as he had hoped. Consequently, what was to be a milestone, a revolutionary way to save patients dying of organ failure or suffering from degenerative diseases such as muscular dystrophy and Lou Gehrig’s disease, has since gone down as little more than a medical oddity, albeit one with all sorts of ethical and philosophical implications.

But in recent years, there’s been renewed talk of perfecting such a procedure. This time it’s spearheaded by Sergio Canavero, an Italian neurosurgeon at the Turin Advanced Neuromodulation Group who has claimed that advances in medical science now make it possible to carry out head transplants that would allow patients to not only survive, but function normally. And with sufficient financial and legal support, he envisions successfully performing a transplant on a human as early as 2017.

“I think we are now at a point when the technical aspects are all feasible,” Canavero told New Scientist.

While expert opinions on Canavero’s claims vary, the possibility isn’t as far fetched as it sounds. James Harrop, director of Adult Reconstructive Spine at Thomas Jefferson University in Philadelphia and co-editor of Congress of Neurological Surgeons, says that the kind of complications the surgeons faced back in 1970 could easily be fixed using today’s methods.

“Technically it’s not any harder than a liver and heart transplant,” he says. “We now have immunosuppressant drugs that might prevent the body from rejecting it. Arteries and the ends of the esophagus can be sewn together. Bones can be fused. As long as the cuts are in place and if you do it high enough, there isn’t that much to hook back up.”

Several challenges remain, however. For Harrop, the biggest hurdle would be to reconstruct the millions of disconnected central nerve fibers that, under normal circumstances, do not regenerate. To do this, Canavero suggests applying a combination of polyethylene glycol, a chemical shown to be effective in getting nerve tissue to bond, with electric muscle stimulation treatment to promote enough growth to connect the pathways that allow signals to travel back and forth between the brain and body.

An outline of the various steps of the proposed operation appears in the latest issue of the journal Surgical Neurology International.

Michael Fehlings, a neurosurgeon who conducts research on neural repair and regeneration at the Fehlings Lab in Toronto thinks that it’s doubtful that there’s any technique capable of spurring the kind of growth necessary to restore motor function in humans. “In animal studies, the degree of functional repair we’ve seen with polyethylene glycol is really very modest and works imperfectly,” he says.

Still Fehlings is optimistic that recent discoveries about the mechanisms that regulate nerve regeneration could someday lead to an effective treatment. He cites, for instance, the finding that proteins Nogo and Rho, which play a vital role in early developmental stages of life, suppresses the body’s ability to heal itself following severe spine injuries. Blocking their activity, scientists observed, led to noticeable nerve outgrowth.

Harrop, meanwhile, feels the most promising developments are happening in the area of stem cells and cell implants. Past trials involving paralyzed rats showed they were able to regain movement after being injected with neural stem cells. And in October, surgeons implanted into the partially severed spine of a paralyzed 40-year-old patient a special set of nerve cells taken from his nose. He now walks again with the assistance of a frame.

Experts, however, caution that we’re still a long way from the point where damaged nerves in the spine can heal themselves by switching off molecules or injecting stem cells. Drugs that target inhibitory proteins are still under study and trials with stem cell treatments haven’t progressed beyond safety studies in animals. “There are many factors with nerve regeneration so there isn’t one magic bullet that can target all the types,” Fehlings says.

So as for the question of how far off we are from actual head transplants, here are a couple statistical estimates offered up by Harrop that should put to rest any thorny ethical questions, at least for now: Chances of simply surviving a head transplant? Roughly 50 percent. And to also walk again? Zero.

“There’s 1,000 things that can go wrong when you’re getting your head put onto someone else’s body,” he says. “And even if you survive that, you’ll live as a quadriplegic and nobody is going to sign up for that.”

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