Head transplantation

Head transplantation is the proposed surgical transfer of a living head onto a body from a different individual, so that the recipient's brain is supplied by a new circulatory and musculoskeletal system. The procedure is more accurately called a body transplant, since the person who would survive is the one attached to the head. No human attempt has been made. The obstacle that makes it implausible is not surgical technique but the fact that a completely severed spinal cord cannot be repaired, and every proposal for performing the operation depends on solving that problem first.

§Animal precedents

The experiments usually cited are older than the current debate and more limited than their reputation suggests.

In the 1950s Vladimir Demikhov, a Soviet surgeon who did foundational work on cardiac and pulmonary transplantation, created dogs bearing a second head and forelimbs grafted onto the neck of an adult host. The grafted heads were conscious and could lap fluid. The animals survived days, dying of rejection.

Robert White, a neurosurgeon at Case Western Reserve University, performed the most technically advanced version in 1970, transferring the head of one rhesus monkey onto the body of another with vascular anastomosis and hypothermic protection. The transplanted head regained consciousness, tracked with its eyes, and responded to stimuli; the animals survived for periods reported as hours to a few days before succumbing to rejection or complications.¹ Crucially, White made no attempt to join the spinal cords. The animals were quadriplegic and ventilated, and White himself described the result as a demonstration that the brain could be maintained on a foreign circulation, not as a functional transplant.

§The modern proposal

In 2013 the Italian neurosurgeon Sergio Canavero published an outline for a human procedure, which he called HEAVEN, with an associated protocol for spinal cord fusion he called GEMINI.² Its elements were a very sharp blade to sever the cord with minimal crush injury, deep hypothermia to extend the brain's tolerance of interrupted perfusion, immediate application of polyethylene glycol as a fusogen to promote membrane fusion between cut axons, and a period of spinal cord stimulation and immobilisation during recovery.

Canavero announced a Russian volunteer with spinal muscular atrophy, who later withdrew. He collaborated with Xiaoping Ren at Harbin Medical University, and in 2017 the pair announced what press coverage described as the first human head transplant. It was a rehearsal on two cadavers: the vessels, cord and tissues of two deceased donors were joined over many hours. Nothing was restored to life, and no functional claim could be tested. Reports of recovery after cord transection and polyethylene glycol treatment in rodents have come almost entirely from the same collaboration and have not been independently replicated.

The reaction from neuroscience and neurosurgery was uniformly negative. The bioethicist Arthur Caplan described the programme as unsupported by science; leaders of professional neurosurgical bodies stated they would not wish the outcome on any patient; spinal cord researchers, including some who had worked with White, characterised the fusion claims as unfounded. In 2024 a promotional concept video for a robotic head-transplant system circulated widely under the name BrainBridge; it was an animation produced outside any research institution and presented no experimental work at all.

What was reported and what was done

The 2017 announcement is a case study in how a procedural rehearsal becomes a claimed achievement. Joining tissues between two cadavers demonstrates that the anatomy can be dissected and sutured. It says nothing about circulation, consciousness, immune tolerance or neurological function, which are the entire content of the proposal.

§The spinal cord problem

Central nervous system axons do not regenerate across a lesion in adult mammals. The reasons are well characterised: inhibitory molecules in myelin debris, a glial scar rich in chondroitin sulfate proteoglycans, an unfavourable growth state in the injured neuron, and the absence of guidance cues that existed only during development.³ Decades of work on chondroitinase treatment, neural stem cell grafts, growth-factor scaffolds and epidural electrical stimulation have produced meaningful partial recovery in incomplete injuries, where surviving fibres can be strengthened. A completely transected cord reconnected end to end is a different problem, and no laboratory has restored voluntary movement after one in a large animal. Peripheral nerves regenerate slowly but genuinely; central tracts do not, which is why the difficulty here is closer to that of Limb regeneration than to that of nerve repair.

Restoring function would require far more than membrane fusion. Millions of axons would have to reconnect, each to a target of the appropriate class, in a topographically correct arrangement, and the resulting circuit would have to be usable by a brain whose motor map was built for a different body. Polyethylene glycol can fuse the membranes of adjacent cut axons in laboratory preparations; it does not perform routing.

The scale of the difficulty was underlined by a 2023 transplant at NYU Langone in which a patient received a partial face transplant that included an entire eye. The globe survived with perfused retina, which was itself a first. Vision was not restored, because the optic nerve is a central tract and could not be reconnected — a single nerve, under ideal circumstances, with the world's attention on it. Restoring sight after optic nerve loss currently requires bypassing the nerve altogether, which is what a cortical visual prosthesis attempts and why the devices in Retinal implants and visual prostheses exist.

§Other barriers

Ischaemia. The brain tolerates warm interruption of blood flow for a few minutes. Hypothermia extends this substantially, and cardiac surgery routinely uses circulatory arrest under deep cooling for limited periods, but the head would need continuous or near-continuous perfusion through a procedure lasting many hours, requiring cross-circulation arrangements of considerable complexity.

Immunology. The immune system resides in the body: bone marrow, thymus, spleen, lymph nodes. A transplanted head is therefore foreign tissue confronting an intact donor immune system, and would face rejection of brain, skull, skin and sensory organs simultaneously, requiring immunosuppression at levels beyond those used in face and hand transplantation. Vascularized composite allotransplantation already has high complication rates from immunosuppression alone, and none of the tolerance strategies developed for Xenotransplantation and conventional grafting has been tested on a target this large. The one established transplant with a planned exit is Uterus transplantation, where the graft is removed after a pregnancy so that immunosuppression can be stopped; nothing comparable is available here.

Autonomic control. Sympathetic outflow to the heart and vasculature descends through the cervical cord. A severed cord produces neurogenic shock with profound hypotension, and if the anastomosis is above the phrenic nerve roots, permanent ventilator dependence. Temperature regulation, bladder and bowel function, and blood pressure control are all lost.

Timing and consent. The procedure requires a beating-heart donor body and a recipient prepared simultaneously in an adjacent theatre, with the donor's family consenting to a use of the body unlike any existing donation category. That body would otherwise supply several transplantable organs to people on a waiting list, so the procedure consumes rather than relieves the deficit described in Organ shortage.

§Ethics and identity

Even granting technical success, the procedure raises questions the surgical literature does not usually face. The resulting person would carry another individual's genome in every cell below the neck, including the gametes, so any children conceived would be genetically the donor's. Legal identity, in most systems, would follow the head, but no statute anywhere addresses the case. The psychological consequences of waking in an unfamiliar body are unknown; limb transplant recipients have occasionally requested removal of a functioning graft, and a whole body is not comparable.

The philosophical question is thinner than it looks. Almost every theory of personal identity locates the person with the brain, so a head transplant is a body transplant and the identity puzzle is mild compared with the cases discussed in Personal identity and continuity and The teleportation problem. The serious ethical objection is not metaphysical but clinical: performing an irreversible operation whose central step has never worked in any animal, on a patient who is typically disabled rather than dying, and whose realistic outcome is death or a state worse than the one they began in. Appeals to Morphological freedom do not settle this, since a right to modify one's own body is generally held to presuppose that the modification is technically possible and the consent adequately informed.

§Where the idea stands

Head transplantation occupies a peculiar position: it is not disproved, merely dependent on a prerequisite that nobody can supply. If complete spinal cord transection became repairable, the achievement would transform the treatment of the hundreds of thousands of people living with spinal cord injury, and that population — not head transplant candidates — is where such a technique would be used first and where its success would be measured.

The motivations offered for the procedure are better served by other approaches. Spinal muscular atrophy, the condition of the volunteer who was announced and then withdrew, now has approved gene therapies of the kind described in Somatic gene therapy, which arrived within a few years of the head transplant proposal and changed the prognosis for the disease it was meant to address. For other degenerative conditions the realistic paths remain gene and cell therapy and assistive technology, including Brain–computer interface control of external devices and powered exoskeletons. For the ambition of escaping a failing body altogether, the relevant articles are Cryonics, Whole brain emulation, Mind uploading and Neuroprosthetics, each of which faces its own unsolved problems but none of which requires reconnecting a spinal cord this year.

§See also

• Neuroprosthetics
• Personal identity and continuity
• Organ shortage
• Xenotransplantation
• Limb regeneration
• Cryonics
• Brain–computer interface
• Morphological freedom

§References