Head Transplants - Shocking Experiments

Animals that have undergone head transplants have not lived long, while in humans, the technique is also very complicated and carries many risks .

The brain is a delicate and fragile organ. The spinal cord, which connects to the brain, does not heal well after being cut. Although head transplants have been performed on animals , most of them have died within hours or days, and at most, months. Some researchers have made headlines by claiming that human head transplants are within reach, but the obstacles are formidable.

The two-headed dog was created by scientist Vladimir Demikhov in an experiment. (Photo: Bettman/Getty)

'I don't think any serious scientist would consider that to be true or scientific ,' Fredric Meyer, a neurosurgeon at the Mayo Clinic, told Live Science on October 19.

Head transplant attempts in history

Scientists have never transplanted a detached brain into an animal. The living brain is too soft and fragile to be removed from one skull and placed in another. Transplanting a detached brain would also require rewiring many of the delicate cranial nerves, a huge challenge. The brain transplants that have been performed are essentially head transplants.

The first attempt took place in 1908, when scientists Alexis Carrel and Charles Guthrie grafted the head of one dog onto another, creating a Cerberus-like creature that lived for only a few hours, according to a 2015 study in the journal CNS Neuroscience and Therapeutics .

It was not a success, but Carrel and Guthrie's work contributed to medicine. Carrel later received a Nobel Prize for his research on vascular reattachment - a technique that helped make organ transplants and limb reattachment possible.

In 1954, Soviet scientist Vladimir Demikhov experimented with upper-body transplants on dogs. Most of these two-headed dogs survived for a few days, with one surviving for 29 days, according to a 2016 study in the journal The History of Neurosurgery. The transplanted heads still functioned, performing tasks like drinking water and responding to visual stimuli. But ultimately, immune rejection killed the dogs.

In the 1960s and 1970s, American neurosurgeon Robert White took head transplants a step further. With rhesus macaques ( Macaca mulatta ) , he experimented with transplanting just the head rather than the entire upper body, and with swapping heads rather than adding a head to the body, according to a 2015 study in the journal CNS Neuroscience and Therapeutics . The transplanted monkeys were able to chew, swallow food, and follow objects with their eyes. However, they were quadriplegic because their spinal cords had been severed and could not send nerve signals to the body. They also died within about 36 hours due to blood circulation problems.

Dr. Ren Xiaoping from Harbin Medical University. (Photo: Red Door News Hong Kong)

The risks

Today, immune rejection can often be prevented with advanced drugs, allowing even highly immunogenic tissues like skin to survive for decades after transplantation. Scientists have also made great strides in revascularization, and it is theoretically possible to maintain blood supply to the brain during head transplant surgery.

In 2015, researcher Xiaoping Ren at Harbin Medical University in China conducted an experiment on mice. He presented a method of cutting one of the two jugular veins in the neck and one of the two carotid arteries to connect the head of the second mouse to the body of the first mouse, leaving the remaining jugular vein and carotid artery to nourish the original head.

But the experiment still has major problems. For one thing, head transplants require cutting and reattaching the spinal cord. Although Ren and his colleagues have found a way to cut the spinal cord low enough for transplanted mice to breathe without a ventilator, there is no concrete evidence in humans that the spinal cord can heal. Some scientists are working on specialized nanomaterials and polymers to repair the spinal cord, but these methods have only been tested in animals with nervous systems different from humans.

Preventing brain oxygen deprivation during and after surgery is also more difficult in humans than in mice because of the size and way human organs are transported. Brain cells begin to die within just five minutes of losing oxygen, according to the National Institute of Neurological Disorders and Stroke.

Plus, there's no research on how to manage pain after a head transplant. Not only is there pain from decapitation, but there's also central neuropathic pain—a type of chronic pain that often occurs after damage to the spinal cord or brain. This type of pain is notoriously difficult to manage, according to a 2016 study in the journal Mayo Clinic Proceedings .

For these reasons, the Ethics Committee of the European Federation of Neurosurgical Societies (EANS) declared human head transplants unethical in 2016. "The risks to the head transplant patient are significant, including the risk of death. There is no definitive evidence for all steps of the procedure, and some steps even lack experimental evidence ," the Ethics Committee concluded.