If You Gave a Man a New Head, Would Life Follow?
If You Gave a Man a New Head, Would Life Follow?
Benjamin Cohen Thomas Jefferson High School for Science and Technology
This article placed 2nd in the 2022 Teknos Summer Writing Contest.
In a hospital near you, a patient is rapidly slipping into organ failure, and prospects of recovery appear slim. As a last-ditch effort, a multidisciplinary surgical team finds a brain-dead motorcycle crash victim and emergently severs both patients’ spinal cords with a thin blade. Racing against the clock of dying neurons and blood loss, the surgeons reattach the organ failure patient’s head to the new body with a cell-fusing polymer and reconnect the blood vessels to restore the oxygen supply. Saved from certain death, the patient regains movement within weeks and returns to normal life. Could this cutting-edge procedure, which goes beyond a single organ transplant to an entire part of a human body with its resident infrastructure, be the answer for patients with intact brains, or even a step towards extending human longevity?
Head transplant trials date back to the early 1900s, with the first success in dogs, although the procedure has not yet been performed in humans [4]. Despite vast promise fueled by over 100 years of research, a head transplant is fraught with technical hurdles and pressing ethical and legal dilemmas. Removing the recipient’s head brings the significant challenge of severing the spinal cord, leading to nearly certain paralysis [4]. By the time the donor’s head is completely transplanted, a prolonged surgery involving the digestive tract, trachea, muscles, and blood vessels, the signal-transmitting axons of spinal cord neurons will have broken down [4, 9]. As short as ten minutes after axons are cut, the severed ends degenerate hundreds of micrometers, making reconnection difficult [9]. An experimental monkey head transplant by Robert White in 1970 illustrates the spinal cord dilemma – while the primate awoke, moved its eyes, and demanded food, it was paralyzed below the neck [17].
However, current research offers solutions to the problem of spinal function. In dogs with severed spinal cords, treatment of the injury with polyethylene glycol, known as a “fusogen” for its ability to rebuild neuron membranes, led to statistically significant recovery on a standardized scale of motor function [13]. In 2016, Italian neurosurgeon Sergio Canavero proposed a head transplant protocol that uses a nanoscale blade to minimize spinal damage, reattaches the cord with a polyethylene glycol pump, and employs electrical stimulation to speed recovery [2]. Modern research also exploits a forgotten anatomical quirk – contrary to conventional wisdom, the brain’s communication to produce movements often involves multiple connected cells within the spinal cord instead of a single neuron, signaling greater potential to restore function than previously thought [2].
Figure 1. “Traditional” motor route (MH1) and the pathway of multiple interconnected cells (MH2). When the spinal cord is severed, cells from MH1 may form new synapses with MH2, contributing to movement recovery after a head transplant [2].
Beyond spinal cord reattachment, a successful transplant would also require connecting the vascular system to the new body and preventing neural death from a lack of oxygen while the head is disembodied. As the brain suffers irreversible damage after 10 minutes without blood, Robert White’s early success in monkeys involved “therapeutic hypothermia” – by bringing body temperature below 25 °C, surgeons slowed the brain’s metabolism and reduced its oxygen demand, allowing for survival [7, 11, 18]. Unfortunately, in this experimental procedure, the sutures holding blood vessels together caused constriction in the jugular veins that drain deoxygenated blood from the head, requiring the monkey to continuously receive anti-clotting medications and leading to death within hours [11]. A group of Chinese neurosurgeons led by Xiaoping Ren applied the new method of “cross-circulation” in a 2015 study, cutting only one pair of the head’s blood vessels instead of both to maintain uninterrupted blood supply to the donor’s brain in a transplant between two rats [15]. Adding a third rat and mechanical pumps for blood supply to the donor’s head improved survival and left the key vessels – the carotid arteries and jugular veins – completely intact [12]. While a human head transplant would likely involve a reduction in blood flow, complications could be managed by lowering body temperature or using fluorine-based blood substitutes that carry large amounts of oxygen [14].
Amidst the surgical technicalities, head transplant surgery remains tenuous from a legal and neuroethical perspective. With surgical advances limited to animal models, are these speculations and rudimentary data sufficient for human implementation? While a significant step forward, Xiaoping Ren’s blood vessel reconnection studies are limited to rats, which are quickly euthanized or display unfavorable survival rates, and the membrane-rebuilding fusogen has only been evaluated in one small human trial of spinal cord transplants [12, 15, 16]. In addition, potential complications have yet to be explored experimentally. To prevent rejection of the head, immune-suppressing medications would be necessary, which may cause unanticipated neurological side effects. The procedure could also result in spinal damage leading to chronic, full-body “central pain” [1, 6]. Medical complications aside, informed consent for a head transplant still remains impossible. Prospective patients, desperate for a lifesaving procedure, are left in the dark regarding risks and outcomes, creating potential issues of human exploitation.
Moving beyond the ethical concern of technical readiness, a head transplant operation axiomatically implies that the brain is wholly responsible for the self, and the body is a mere appendage that can be swapped while maintaining personal identity. However, science challenges this perspective — a head transplant entails switching the microbiome and enteric nervous system, which could subtly and unpredictably impact the recipient’s sense of self. The enteric nervous system has a bidirectional link to the brain, as evidenced by the impact of microbiome changes on both brain and gut functions; around 95% of the body’s serotonin is synthesized by intestinal endocrine cells, with many other neurotransmitters produced by intestinal bacteria [10]. “Psychological rejection” of a head transplant is a significant consideration, as it remains impossible to predict a patient’s physical reaction to being newly embodied or the potential struggle to integrate the acquired body into their sense of self until after the procedure takes place [19].
As a head transplant requires monumental coordination of multiple surgeons and millions of dollars, it is crucial to recognize concerns over resource allocation due to the operation’s experimental nature and potential to cause death or waste lifesaving donor organs [8, 20]. Even if the spinal reconnection protocol is mastered, ethical quandaries on whether to treat large populations with spinal cord injuries or just a single person would emerge. Due to the massive investments of capital and human resources, the procedure might only serve the socioeconomically advantaged [5]. Head transplantation stands so far ahead of its time that the legal and regulatory framework has not caught up; the procedure could even be classified as homicide due to the surgical decapitation involved. This operation would also make it difficult to define the identity of the recipient, who would assume the donor’s fingerprints and genetic makeup, leading to a host of ethical and legal disputes [3, 19, 20]. Head transplant surgery seems like something out of science fiction, and rightfully so; with a number of technical and moral hurdles, head transplantation should be treated with extreme caution in the face of its revolutionary implications.
References
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