A full brain transplant, where one person’s brain is removed and placed into another person’s body, has never been performed in humans and remains beyond the reach of current medicine. The obstacles are not just surgical but biological: reconnecting a severed spinal cord, keeping billions of neurons alive during the transfer, managing an immune response from the new body, and reattaching the intricate web of cranial and autonomic nerves that link the brain to everything from heartbeat to digestion. Researchers have attempted head and brain transplants in animals since the early 1900s, and those experiments reveal just how formidable each barrier is.
What Animal Experiments Have Shown
The history of brain and head transplantation in animals stretches back over a century, and the results have been consistently grim. In 1908, surgeons Alexis Carrel and Charles Guthrie performed the first dog head transplantation, grafting one dog’s head onto another dog’s neck and connecting the arteries so blood flowed to both heads. The transplanted head had been without blood flow for about twenty minutes. It showed some reflexes early on but deteriorated quickly, and the animal was euthanized within hours.1PubMed Central. The history of head transplantation: a review
In the 1950s, Soviet scientist Vladimir Demikhov pushed further, creating two-headed dogs that could move, see, and even lap up water. His longest surviving animal lasted 29 days, but most died within a few days, largely because of immune rejection. The immunosuppressive drugs we have today simply did not exist then.1PubMed Central. The history of head transplantation: a review
American neurosurgeon Robert White took a different approach in the 1960s and 1970s. Rather than transplanting an entire upper body, he attempted to graft isolated canine brains onto recipient dogs’ neck blood vessels. The dogs survived between six hours and two days. White then moved to primates, performing cephalic exchange transplants between monkey heads and monkey bodies under deep hypothermic conditions. The transplanted heads could chew, swallow food, track objects with their eyes, and bite when stimulated, but survival ranged from only six to 36 hours.1PubMed Central. The history of head transplantation: a review 2PubMed. From Hypothermia to Cephalosomatic Anastomoses: The Legacy of Robert White (1926-2010) at Case Western Reserve University of Cleveland
A crucial detail about every one of these experiments: none of the animals regained voluntary movement of the donor body. The spinal cord was never reconnected. The transplanted heads were, functionally, conscious brains sitting atop paralyzed bodies.
The Spinal Cord Problem
If there is a single reason brain transplants remain in the realm of science fiction, it is the spinal cord. To transfer a brain to a new body, you would need to sever and then rejoin the spinal cord so that signals from the brain can reach the muscles and organs below. Adult neurons in the spinal cord do not regenerate the way skin or bone cells do. After a traumatic spinal cord injury, the local environment around the damaged area actively blocks regrowth. Molecules on the surface of remaining myelin sheaths, along with scar tissue that forms at the injury site, create a chemical barrier that prevents severed nerve fibers from extending back across the gap.3PubMed Central. Axonal Regeneration after Spinal Cord Injury: Molecular Mechanisms, Regulatory Pathways, and Novel Strategies
One substance that has generated interest is polyethylene glycol, or PEG, a common polymer used in everything from skin cream to industrial solvents. In laboratory models of spinal cord injury in guinea pigs, applying PEG directly to a crushed spinal cord sealed damaged nerve cell membranes, reduced harmful free radical production, and restored measurable electrical signals through the injured area in every treated cord.4PubMed. Anatomical repair of nerve membranes in crushed mammalian spinal cord with polyethylene glycol 5PubMed. Polyethylene glycol immediately repairs neuronal membranes and inhibits free radical production after acute spinal cord injury PEG works as a “fusogen,” essentially gluing torn cell membranes back together, which also tamps down the oxidative damage that cascades after injury.6PubMed Central. Polyethylene glycol in spinal cord injury repair: a critical review
The Italian neurosurgeon Sergio Canavero, who announced plans for a human head transplant, cited PEG as the key to fusing a severed spinal cord. But there is a wide gulf between repairing a crush injury where some cellular continuity remains and fusing a cord that has been cleanly cut in two. In a crush, the structural scaffolding of the nerve fibers is still partly intact, giving PEG something to seal. In a full transection, as a brain transplant would require, there is no such scaffold. No laboratory has demonstrated PEG-mediated restoration of voluntary movement across a completely transected mammalian spinal cord, and the leap from guinea pig bench experiments to human surgery is enormous.
Keeping the Brain Alive During Transfer
The human brain consumes about a fifth of the body’s oxygen supply. Cut off blood flow for even a few minutes at normal body temperature and neurons begin to die. A brain transplant would require disconnecting the brain from one body’s blood supply, moving it, and hooking it up to a new circulatory system, all before irreversible damage sets in.
The closest analogue we have in clinical practice is deep hypothermic circulatory arrest, a technique used in complex heart and aortic surgeries. The patient’s body temperature is dropped dramatically, which slows the brain’s metabolic rate and buys surgeons a window during which blood flow to the brain can be temporarily stopped.7PubMed Central. Deep hypothermic circulatory arrest Robert White used this same principle in his monkey experiments.
But the window is narrow, and it comes with costs. Studies of adults who undergo this technique show that circulatory arrest lasting 25 minutes or more is a significant predictor of later problems with memory and fine motor skills.8PubMed. Neuropsychologic outcome after deep hypothermic circulatory arrest in adults Other research has found that when the arrest period is kept relatively short, neurocognitive function can be effectively preserved, though some decline in memory acquisition and recall still shows up in both groups of patients who undergo cardiac surgery, whether they experienced circulatory arrest or not.9PubMed. Deep hypothermic circulatory arrest effectively preserves neurocognitive function In neonates and infants, the technique has been linked to neurodevelopmental problems that surface later in childhood.10Annals of Thoracic Surgery. Cerebral Protection in Neonates and Infants Undergoing Deep Hypothermic Circulatory Arrest and Cardiopulmonary Bypass
A brain transplant would almost certainly require a far longer period of disconnection than any cardiac procedure demands. The microsurgical work needed to connect arteries and veins to a new body, verify flow, and ensure no clots form would take hours, not minutes. And once blood is restored, the brain faces another danger: reperfusion injury, where the sudden return of oxygenated blood paradoxically triggers inflammation and cell death. A related complication, cerebral hyperperfusion syndrome, occurs in a small percentage of patients after carotid artery procedures and can cause seizures or brain swelling due to the loss of normal blood flow regulation.11PubMed Central. Uncommon Etiology for Seizure: Cerebral Hyperperfusion Syndrome Scaling that risk up to a full brain transplant is a sobering thought.
Immune Rejection and the Brain’s Unusual Defenses
Every organ transplant triggers an immune battle between the recipient’s body and the foreign tissue, and the brain adds its own twist. The brain is sometimes described as “immune privileged,” meaning it is partly shielded from the full force of the body’s immune system. The blood-brain barrier, a tightly sealed layer of cells lining the brain’s blood vessels, restricts which immune cells and molecules can enter. Experiments in rats have shown that when foreign neural tissue is grafted into the brain and the blood-brain barrier remains intact, the graft can survive for extended periods. But when the barrier is artificially opened, the immune system floods in and destroys the graft, accompanied by a surge of rejection-signaling molecules on surrounding cells.12PubMed. The blood-brain barrier protects foreign antigens in the brain from immune attack
The catch is that any transplant surgery would inevitably disrupt the blood-brain barrier. Cutting and reattaching blood vessels, handling brain tissue, and the inflammatory response to surgery itself would all compromise that protective seal. Studies tracking the timeline of rejection in brain grafts have found that once the barrier breaks down, lymphocytes and macrophages infiltrate the graft within days.13PubMed. Integrity of the blood-brain barrier in retinal xenografts is correlated with the immunological status of the host
Complicating matters further, the brain’s immune response varies by region. Research on neural cell transplants in mice has found that grafts placed in the striatum, a deep brain structure involved in movement, were completely destroyed by immune cells. Grafts placed in the hippocampus, the brain’s memory center, fared much better and survived for at least two months, with far less immune cell invasion. But when a different cell type (astrocytes rather than neural precursors) was grafted into the hippocampus, the immune system attacked aggressively again.14PubMed Central. Brain Region-Dependent Rejection of Neural Precursor Cell Transplants The brain’s immune privilege, in other words, is partial, patchy, and context-dependent. It is not a reliable shield for a transplanted organ.
The Nerves You Never Think About
Discussions about brain transplants tend to focus on the spinal cord, but the brain connects to the body through far more than just that one cable. Twelve pairs of cranial nerves exit the base of the brain and serve functions ranging from vision and hearing to facial movement and taste. Then there is the vagus nerve, which wanders from the brainstem down through the neck and into the chest and abdomen, regulating heart rate, digestion, breathing rhythm, and immune responses. The vagus nerve’s organization is extraordinarily complex, with different fiber types serving different organs in a highly specific topographic arrangement.15PubMed Central. Development and regeneration of the vagus nerve
Reconnecting even one severed peripheral nerve is a painstaking microsurgical procedure with uncertain outcomes. Reconnecting all twelve cranial nerve pairs and the vagus nerve, while ensuring that each fiber finds its correct target in the new body, is a challenge that current surgical techniques cannot address. Get the vagus nerve connections wrong and the brain cannot properly regulate the new body’s heart, lungs, or gut. Get the cranial nerves wrong and the person may not be able to see, swallow, speak, or control their facial expressions, even if the brain itself is unharmed.
Would You Still Be You?
Even if every surgical barrier were somehow overcome, a brain transplant raises a question that medicine alone cannot answer: would the person who wakes up in the new body still be the same person? The procedure has been described as testing “not only our surgical limits, but also the social and psychological boundaries of physical life.”16International Journal of Surgery. Surgical, ethical, and psychosocial considerations in human head transplantation
From a neuroscience perspective, your identity, memories, and personality are encoded in the brain, so transplanting a brain to a new body should, in theory, transfer “you.” But identity is not purely cerebral. Your body constantly feeds sensory information back to the brain, shaping your sense of self. Spinal cord injury patients sometimes experience phantom sensations, feeling limbs that no longer send signals, and these phantom perceptions can be vivid and distressing. One case described a patient with a complete spinal cord injury who, six days after the injury, felt an extra pair of phantom legs originating at his hips, along with severe pain in these nonexistent limbs.17PubMed Central. Atypical supernumerary phantom limb and phantom limb pain in a patient with spinal cord injury: case report
A brain transplant recipient would face an extreme version of this disorientation. The brain would receive sensory signals from a body it has never inhabited, with different proportions, different proprioceptive feedback, and potentially a different hormonal profile. Whether a person could psychologically adapt to that experience is completely unknown. Even heart transplant recipients sometimes report feeling changed by the procedure, though there is no agreed-upon biological mechanism for that. A brain transplant would involve a wholesale mismatch between the brain’s lifelong body-map and the actual body it now occupies.
Technologies That Chip Away at the Barriers
No single technology is close to making brain transplants possible, but several lines of research are slowly eroding individual barriers in ways that matter for spinal cord injury patients right now, even if a full transplant remains out of reach.
Epidural electrical stimulation has produced some of the most dramatic results. By placing electrodes on the surface of the spinal cord below the level of injury and delivering carefully patterned electrical pulses, researchers have restored voluntary leg movement in people with complete spinal cord injuries, meaning injuries where no motor signals were getting through at all. In one study, nine people with chronic spinal cord injuries regained the ability to walk with this approach combined with rehabilitation training.18PubMed Central. The neurons that restore walking after paralysis Other clinical investigations have confirmed that epidural stimulation can restore some voluntary movement and other neurological functions below the injury level.19PubMed Central. Epidural electrical stimulation for spinal cord injury 20PubMed. Epidural spinal cord stimulation as an intervention for motor recovery after motor complete spinal cord injury
This technology does not repair the spinal cord. Instead, it activates dormant spinal circuits below the injury, essentially bypassing the damaged area. For a hypothetical brain transplant, epidural stimulation could theoretically allow some motor function even without full spinal cord fusion, though the control would be far cruder than normal movement.
Brain-computer interfaces represent another workaround. Rather than reconnecting nerves physically, these systems read electrical activity from the brain and translate it into commands for external devices or direct stimulation of muscles. Systems designed for rehabilitation have demonstrated the ability to interpret a patient’s intended movements with accuracy above 95 percent and use that information to trigger muscle contractions in paralyzed limbs through electrical stimulation devices.21Semantic Scholar. Design of intelligent rehabilitation system based on Brain-Computer Interface In the far future, implanted interfaces might serve as an electronic bridge between a transplanted brain and its new body, but the technology is still largely experimental and limited to restoring simple movements.
Cerebral Organoids and Partial Brain Repair
Rather than transplanting an entire brain, some researchers are exploring a more incremental strategy: growing small clusters of brain tissue in the lab and implanting them into damaged areas. These clusters, called cerebral organoids, are derived from stem cells and develop into three-dimensional structures containing multiple types of neurons.
In mouse models of traumatic brain injury, transplanted human cerebral organoids survived in the damaged area, differentiated into various types of neurons, extended long projections, and showed spontaneous electrical activity. The mice that received the organoids showed improved spatial learning and memory compared to untreated animals.22PubMed Central. Human Cerebral Organoid Implantation Alleviated the Neurological Deficits of Traumatic Brain Injury in Mice Similar results have been seen in stroke models: organoids transplanted into the border of infarcted brain tissue survived for months, sent axons to distant brain targets, integrated into the host neural circuit, and eliminated sensorimotor deficits, while transplanting the same cells in dissociated form failed to repair the damage.23npj Regenerative Medicine. Cerebral organoids transplantation repairs infarcted cortex and restores impaired function after stroke
Organoid transplants also appear to integrate with the host’s blood supply more effectively than single-cell transplants. When grafted into lesioned mouse cortex, cerebral organoids developed robust vascularization from the host brain and maintained a large pool of stem cells capable of producing multiple neuron types.24PubMed Central. Vascularization and Engraftment of Transplanted Human Cerebral Organoids in Mouse Cortex
These experiments are still in mice, and the organoids are tiny compared to a human brain. But they suggest a future where instead of replacing the entire brain, damaged regions could be patched with lab-grown tissue that integrates into existing circuits. For conditions where a specific brain area is destroyed by stroke, trauma, or degeneration, this piecemeal approach may eventually prove far more practical than the science-fiction dream of a whole-brain swap. The organoid work also sidesteps the spinal cord problem entirely, since the repair happens within the skull using the brain’s existing connections to the body.
Why “Head Transplant” and “Brain Transplant” Are Not the Same Thing
Popular coverage often blurs the line between head transplants and brain transplants, but they are substantially different procedures with different challenges. In a head transplant, the entire head, skull, face, and all, is moved to a new body. The brain stays safely inside its original skull, protected by its own blood-brain barrier infrastructure and still connected to its original cranial nerves (at least the ones that do not exit the skull). The surgical challenge centers on reconnecting the spinal cord and the major blood vessels in the neck.
A true brain transplant would require removing the brain from the skull, which means severing every cranial nerve at the base, disconnecting the brain from the pituitary gland (the body’s master hormonal controller), and detaching the brain from the meninges that cushion and protect it. The brain would then need to be placed into a new skull, reconnected to a completely different set of cranial nerves, re-anchored to a new pituitary stalk, and re-enclosed in membranes that form a watertight seal for cerebrospinal fluid. Every one of those steps adds risk and complexity that a head transplant avoids.
This is why serious proposals in the medical literature discuss body-to-head transplantation rather than brain transplantation. The goal, as researchers have framed it, would be to sustain the life of people who suffer from terminal diseases but whose heads and brains remain healthy, giving them a functional body when their own has failed.16International Journal of Surgery. Surgical, ethical, and psychosocial considerations in human head transplantation Even by that less extreme standard, no verified human procedure has been performed. Canavero claimed in 2017 to have carried out a head transplant on a human cadaver in China, but no peer-reviewed data from the procedure has been published, and the neurosurgical community has widely dismissed the claim as unsubstantiated.
For the foreseeable future, the technologies most likely to help people with failing bodies are not transplants of any kind, but advances in nerve stimulation, brain-computer interfaces, lab-grown tissue patches, and better immunosuppression for the organ transplants we already perform. The whole-brain transplant remains one of medicine’s most vivid thought experiments, useful for illuminating what we do not yet understand about the nervous system, identity, and the limits of surgical repair, but nowhere near clinical reality.