What to Expect From a Head Transplant

It may sound like something out of science fiction, but as medical science advances, there might there one day be a role for a head transplant. Head transplant would theoretically involve surgically removing the head of someone with a terminal illness and attaching their blood vessels, muscles, trachea, and esophagus with those structures of the donor body. The most recently proposed head transplant procedure also involves fusing the recipient and donor’s spinal nerves. 

Subsequent spinal surgery and conceivably extensive physical therapy could ideally recover both sensation and motor function. However, functions like breathing and eating would need to be transiently supported by a ventilator and feeding tube before the connections between the brain and body are adequately restored. 

Along with the uncertainties of the medical benefits of a head transplant, there are also likely risks associated with the procedure, including chronic neuropathic pain, rejection of the donor body, and organ toxicity of immunosuppressants.

As surgical methods have become more refined and consistent, procedures like transplantation of tissues and organs as well as replantation (reattachment of a severed body part) have had relatively high success rates. With over a century of advances in transplantation, some patients and surgeons have begun to look at head transplantation as a potential solution to progressive diseases that become terminal with time but do not impact the function of the brain. 

There has been limited success in head transplant procedures performed on mice, dogs, and monkeys. Many surgeons have been critical of the current level of success that has been achieved in animal models.

Moreover, the medical community has questioned whether the techniques are developed enough to practically or ethically perform a head transplant on a human subject. The efficacy of using a donor body for one recipient rather than multiple organ transplants has also been disputed. Surgeons Sergio Canavero and Xiaoping Ren, among others, plan to attempt the first human head transplant in coming years. What is the theory that supports their ambitions?

Reasons for a Head Transplant 

In general, a head transplant would be indicated when an individual’s brain remains normal but the body’s function is severely compromised or is anticipated to fail in ways that affect long-term survival. It would not be used to extend someone’s life when the body fails from natural aging processes.

People who are young may be considered candidates if they have suffered an acute spinal cord injury leading to quadriparesis, for example, or if they have a progressive, degenerative disease that does not affect the brain. Muscular dystrophy leads to a progressive loss of respiratory function and mobility in children and young adults, but does not affect the brain. People with inoperable or advanced cancers that have not metastasized to the brain have also been considered for head transplant as there is limited further treatment at that stage.

Head transplant would be used as a last-line treatment when other medical interventions have failed. It would be limited by the availability of donors.

Who Is Not a Good Candidate? 

It is difficult to anticipate who may or may not be an ideal candidate for a head transplant. These exclusion criteria would be developed once the procedure is implemented and the potential risks for complications and failure are better understood.

As noted, abnormalities affecting the brain would likely be an exclusion criterion. Someone undergoing a head transplant would need to have a great deal of social support, including continuous medical care and assistance with activities of daily living, for months if not years. The costs associated with the procedure itself would also likely be extensive, and as an initially experimental intervention, it may not be covered by health insurance.

Donor Recipient Selection Process

A body donor would be someone who has suffered brain death, likely from a catastrophic injury, yet is artificially sustained until the head transplant can occur. This would preserve the health and function of the body’s tissues, which should otherwise be normal. The donor for a head transplant procedure would further need to match the recipient’s height and immunotype. 

The intent to serve as a body donor would likely need to have been stated prior to the injury. In some places, organ donation is the default, but current law does not likely address the possibility of body donation.

Currently, there are no formalized indexes or donation systems set up for head transplantation, as it is a yet unproven procedure.

Before Surgery

As with any surgery, and more specifically with any organ transplant, there is an extensive process required to prepare the recipient for the procedure. This may include a complete medical and psychiatric evaluation. It must be demonstrated that a head transplant is both necessary and safe and that the recipient of a body donation is likely to have long-term success.

One might imagine a formal neurological evaluation with imaging to include a computerized tomography (CT) scan and magnetic resonance imaging (MRI) of the brain as well as an electroencephalogram (EEG). A cardiovascular assessment of the vessels of the head and neck may also be important with CT angiography or ultrasonography likely to have a role. Further assessments by an ear, nose, and throat (ENT) specialist and even a dentist may have a role to screen for abnormalities. Even a sleep study to look for obstructive sleep apnea may be important.

Systemic assessments of health may be important, identifying chronic medical disorders that may affect transplant success. For example, testing for chronic infections, diabetes, thyroid dysfunction, and other abnormalities may be necessary. It may be important to exclude those who smoke, consume alcohol, or use other illicit drugs.

To have a head transplant, it may be important to completely eliminate the immune system of the donor body to prevent rejection. This could be accomplished with radiation and antibodies, then the recipient’s own bone marrow would be used to replace the immune system of the donor. Obstacles to this include keeping the donor body alive without an effective immune system in the weeks before the head transplant and negative effects on the neural cells that will be fused with the recipient's during the transplant.

Surgical Process

No head transplant has yet been performed on a person. Nevertheless, surgeons interested in performing the procedure have prepared protocols planning the steps of a future head transplant. However, there have been many critiques by other medical experts of the significance or relevance of experimental research cited in the proposed protocol for human head transplantation, as surgical precedents set in animals are not always applicable to human surgery. Many of the planned tools and techniques, such as spinal cord transection, chemical fusogens (agents that allow cells to fuse together), and spinal cord stimulation have not yet been well studied for their relevant use in human head transplantation.

In the proposed protocol, four surgeon teams would work together on the recipient and donor simultaneously.

Supporting Vital Functions of the Body

Surgery preparation would begin with a tracheotomy, insertion of a ventilation tube, and use of a ventilator to stabilize the donor body when the connection between the brain and body is broken. Blood oxygen, body temperature, and blood pressure would be monitored as the surgery progresses.

Continuous blood flow to the donor body during the transfer is important to maintain normal oxygen levels in the donor body’s tissues and organs. Major blood vessels would have plastic tubes inserted (this cannulation would create a shunt). Blood flow would then be redirected to a life support machine called an extracorporeal membrane oxygenation (ECMO) machine that supplies oxygen to the blood and circulates it independent of the heart and lungs. 

The temperature of the donor’s spinal tissue would be lowered by inserting cold solutions into the space along the vertebral wall (epidural) or between the dura mater and arachnoid membrane of the spinal cord (subdural).

As the temperature of the spinal tissues drops, the body becomes ready for the transplantation.

Preparing the Recipient 

Meanwhile, the head of the recipient is anesthetized (and brain activity is limited) with the administration of barbiturate or propofol. Brain activity is monitored via EEG throughout the process. The recipient then undergoes similar surgical preparation as the donor. 

Blood flow from the head is diverted to an ECMO machine to make it independent of the heart and lungs. 

Alternatively, interruption of blood flow could be avoided by shunting blood flow from the carotid arteries and jugular veins of the recipient head and donor body. Both methods retain continuous circulation of blood to the brain which is required to prevent stroke and brain death.

Inducing hypothermia in the brain is key to prevent damage during the procedure. Lower tissue temperatures decrease the risk of low oxygen damage (anoxia) to the brain by slowing its metabolic rate. The brain’s temperature can be lowered by biventricular cooling, intra-arterial cooling, or related techniques. A cooling helmet then maintains hypothermia of the brain.

Additional neuroprotective substances like perftoran, hydrogen sulfide, or lidocaine could be circulated to limit anoxia in the brain.

When the recipient head and donor spinal cord have reached a low enough temperature (profound hypothermia), the transplantation process begins.

Three Phases of Surgery

A head transplant surgery would potentially have three phases: 

Anterior Approach

To begin, the neck area of the recipient and donor would be opened up, exposing the muscles and the blood vessels of the neck and spine. Muscles and blood vessels would be marked so that they can later be connected between recipient and donor. 

The trachea and esophagus would be cut, while the laryngeal nerves of the recipient would be kept intact.

Posterior Approach

The recipient and donor would both be positioned so that the back of the spine can be accessed. A cut along the length of the upper spine would be made, and the body of the target vertebrae and the dura tissue beneath would be cut to expose the spinal cord. 

Spinal Anastomosis

A scalpel would be used to cut through the spinal cord. An extra length of spinal cord would be preserved to allow for adjustment cuts to match the length and attachment points of both the recipient and donor. When the recipient’s head is removed, the blood would be drained from the head (exsanguinated). The head’s blood vessels would be flushed with Ringer’s lactate, which will prevent blood coagulation from damaging the brain.

The head and body would be aligned and a titanium plate would be placed on the front of the neck area to stabilize the head and body. The main blood vessels of the recipient would then be connected to the donor’s circulatory system and begin to receive blood. 

The deepest muscles would be attached with sutures, followed by the esophagus, trachea, and outer muscles.

The body would then be turned over to finish the attachment of the spinal cord. The adjustment cuts would be made to match the length between the recipient and donor, then the cut ends of the spinal cords would be fused using a glue composed of fusogens and then sutured. Treatment with fusogens would ideally allow for the damaged neurons to be repaired and for the patient’s brain to form a neural connection with the donor body.

Once the spinal cord is connected, the protective dura of the spine would be sewn back together. It is also possible that the insertion of a pacemaker-like spinal cord stimulation (SCS) apparatus into the epidural space behind the spine could be used to promote neuron recovery.

Complications

The most likely complication related to a head transplant would be failure of the procedure to establish the required connections to preserve normal bodily functions. 

This may manifest in loss of cerebral blood flow leading to ischemia and brain damage, stroke, or brain death. A loss of oxygen supply to the brain could be similarly injurious. Disruption of the blood-brain barrier may lead to infection or injury to the brain’s tissues.

The body may suffer similar complications, with a loss of blood flow or oxygen causing organ damage or failure. 

If the nervous system fails to reconnect, this may affect movement, sensation, and the function of organs (potentially leading to paralytic ileus, neurogenic bladder, neurogenic bowel, or other problems).

The immune system may reject the transplanted organ, effectively creating a destructive battle of attrition between the head and new body.

After Surgery

Surgery would likely be followed by prolonged monitoring in the intensive care unit (ICU). The head, neck, and spine would be stabilized to maximize spinal cord fusion. 

Breathing and circulation would be mediated through life support systems, and feeding would need to be supplied through a jejunostomy tube while movement recovers. 

As recovery progresses, physical therapy similar to rehabilitation for quadriplegia would be used to promote neural connections between the brain and the new body. The restoration of diaphragm function, important for independent breathing, would be continually assessed.

Prognosis

There is no reliable information to predict how a human would do after a head transplant has been performed. One likelihood is that lifelong immunosuppression would be necessary to prevent rejection of the donor body. Animals that have received head transplants without use of immunosuppression survived for limited periods of time, from several hours to 29 days at the most.

Risks linked to immunosuppression in organ transplants currently performed include a moderately increased risk of infection or cancer.

Immunosuppressants that have been considered for preventing rejection of the head or donor body include:

• Sirolimus
• Tacrolimus
• Cyclosporin A
• Belatacept
• Rapamycin 
• Prednisone 
• Mycophenolate Mofetil

High dose, long-term use of immunosuppressants could cause secondary damage to the donor body’s organs, such as the kidneys, depending on the specific drugs used and amounts needed to prevent rejection. Several of the listed immunosuppressants do not have known toxicity, but will need to be tested for their effects when used in combination for head transplantation.

Support and Coping

Psychological counseling would likely be beneficial while adjusting to a new body, coping with side effects from the surgery, and major lifestyle changes. Coping with unfavorable outcomes (i.e., problems recovering sensation, mobility, or bowel and bladder function) would also be likely to pose psychosocial obstacles. 

A Word From Verywell

It is unlikely that a head transplant could be performed in humans in the near future. Nevertheless, the theoretical exploration of the topic, including the ethical and technical considerations, may be an interesting exercise. These thought experiments prepare us for an actuality that may eventually be possible as medical science advances.