Jul 02 2013

Follow Up on Head Transplants

I recently wrote about the implausibility of performing whole head or brain transplants.  By coincidence (I think, unless this paper triggered the question to which I was responding) a recent paper proposes how to successfully complete a human head transplant.

Italian neurosurgeon Sergio Canavero writes:

“The greatest technical hurdle to [a head transplant] is of course the reconnection of the donor’s (D)’s and recipients (R)’s spinal cords. It is my contention that the technology only now exists for such linkage…. [S]everal up to now hopeless medical connections might benefit from such a procedure.”

To recap my prior post – prior surgeons have attached the head of a monkey or dog onto the body of another. I argued that these were not really transplants but grafts, as the body was providing blood to the severed head, but there was no functional connection. The primary hurdle to achieving any kind of functional connection is the spinal cord.

Canavero is arguing that with existing technology we can make a clean sharp cut of the donor and recipient spinal cords and this will allow them to connect together, providing functional control of the severed head to the donor body (what he calls a cephalosomatic linkage).  He adds that a plastic like polyethylene glycol can be used to “glue” the two spinal cord ends together and encourage their regeneration.

We are making some progress in getting spinal cords to regenerate, but I think Canavero is vastly overstating where we currently are. For example he cites a recent rat study in which partial function was restored. In this study, however, only bladder function was partially restored, not motor function.

Spinal cord regeneration research is exciting. Researchers have identified the likely reasons for why peripheral nerves regenerate and spinal cords do not. This at least suggests possible treatment strategies. It may be possible to eventually get damaged spinal cord to regenerate to the point of functional recovery. This research, however, is progressing with baby steps. Eventually these baby steps will likely add up to a viable treatment, but that is still years away.

Canavero’s point that a clean surgical cut will repair more easily than traumatic damage seems valid. But it is not clear, and in fact is pure speculation, that this difference will be sufficient to restore meaningful function.

Also, transplanting a head introduces another variable – that of acceptance vs rejection of a graft from another person. Transplant rejection is an issue, and it is not clear if this will interfere with spinal cord regeneration.

I still maintain that once we know how to coax a spinal cord to regenerate in order to connect two severed ends, it will likely be easier to repair an existing spinal cord than to transplant a head onto a new body. Still, there are some conditions, like muscular dystrophy, where the spinal cord is not the problem (the muscles are) and therefore a head/body transplant would offer a possible solution.

If Canavero wishes to support his speculation, the next step would be doing full head transplants in rats or larger animals to demonstrate his principle. I, of course, would be interested to see the results.

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