Drawing The Human Head Hogarth

Are human head transplants possible?

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Futurama head jars

A bold project has just been announced which seeks to achieve the first human head transplant. Code-named HEAVEN, for Head Anastomosis Venture with Cord Fusion, the effort is being led by Dr. Sergio Canavero, from Turin, Italy. In a new paper published in the open-access journal, Surgical Neurology International, Canavero claims that many technical hurdles to successful transplantation have now been cleared. Surgically speaking, many of the micro-knitting procedures to bridge different tissues are now routine — the problem is getting the nerves of the spinal cord to regrow, and find their correct partners.

Head transplantation is nothing new. Russian doctors performed experiments back in the 1950s involving successful transplantation of an extra head onto a dog. Our own Robert White, from Case Western Reserve University (CWRU), transplanted the head of a monkey in 1970. The animal then survived on its new body for 8 days. While the monkey-head amalgam had no nervous control over it's new body, the sensory and motor functions of the head itself, were largely intact. Efforts to bridge a severed spinal cord are still being pursued at CWRU, with some significant advances. Re-enervation of the bladder and the diaphragm has been achieved in rats, raising hopes that the same may be done for paralyzed humans.

While breathing and urinating on your own is difficult to overvalue, a head transplant can hardly be considered satisfactory if you can't feel and move the rest of your new body. One major problem with current transplantation/regrowth efforts is that getting nerves to make the right handshakes is not something that can be done with the tools available to a surgeon. Furthermore, there is no magic pixie dust that can be sprinkled onto the blunt ends of a severed cord to get them to properly regrow. Surprisingly, that has not stopped researchers from trying to chemically create the perfect growth environment.

For the recent rat studies, two chemicals in particular, chondroitinase and FGF, were used to incentivize the reconnection process. Additionally, the laxative PEG (polyethylene glycol), and even melatonin, were shown to be of service in helping nerves regenerate. As far as concocting the perfect growth cocktail, however, you can pretty much pick your poison. Thousands of studies have been published on axon growth, and probably as many unique molecules explored. Basically, what they all boil down to is that you need to tenderize the Tsahaylu. Until we can understand what it is that makes a nerve want to strike out on its own, and bulldoze its way through an extracellular jungle to reach a target perhaps meters away (at least in the case of the nerves reaching the fluke of a fin whale), our efforts to control that innate imperative can have only limited success.

Spine Sure, one might argue that nerves, once tethered to expanding or elongating tissue, are simply along for the ride like sea turtles crossing an expanding expanse of ocean to reach once-nearby nesting ground — but still — they have made the choice, generation after generation through evolutionary time, to hang on. What neural caviar might the whale fluke posses that beckons a certain type of axon to come hither at such disproportionate metabolic cost? What other hyper-inflated yet irresistible molecular tulips might be placed at the disposal of the genetic engineer? At the scale of the spinal cord, a finer-grained approach to regrowth will be needed to achieve anything beyond a simple binary toggling of a few control points. This means some kind of robot-assisted microsurgery will be necessary to install hundreds, or thousands, of splinted junctions with appropriate molecular signposts to guide the nerves.

In the past, research has largely focused on neurons and the growth of their axons, but it is now appreciated that it is the myelinating cells, the cerebral lion tamers, that ultimately determine the stable architecture of the spinal cord. At the macroscopic level, there are still many hurdles to be surmounted from a patient comfort perspective. Keeping the freeze on consciousness while things are wiring up is generally believed to be a good idea. White's original work describes a method of intraventricular cooling to keep the brain hypothermic, and the HEAVEN protocol concurs. The exact spinal level chosen for transection is still under discussion, although it appears that somewhere around cervical level C5 or C6 would be ideal.

Head transplant surgery, if it is ever done, will not likely be a one-size-fits-all procedure. That it is now possible to have a serious and open discussion of the particulars of any such procedure is a sign that remarkable advances have been already made both at the technological level, and at the societal level.

Now read: Intracranial nanowires: The basis of implanted brain-computer interfaces

Research paper: DOI: 10.4103/2152-7806.113444 – "HEAVEN: The head anastomosis venture Project outline for the first human head transplantation with spinal linkage (GEMINI)"