A head transplant is an experimental surgical operation involving the grafting of one organism's head onto the body of another; in many experiments the recipient's head was not removed but in others it has been. Experimentation in animals began in the early 1900s. As of 2017 no durable success had been achieved.
There are three main technical challenges. As with any organ transplant, managing the immune response to avoid transplant rejection is necessary. Also, the brain is highly dependent on continuous flow of blood to provide oxygen and nutrients and remove waste products, with damage setting in quickly at normal temperatures when blood flow is cut off. Finally, managing the nervous systems in both the body and the head is essential, in several ways. The autonomic nervous system controls essential functions like breathing and the heart beating and is governed largely by the brain stem; if the recipient body's head is removed this can no longer function. Additionally each nerve coming out of the head via the spinal cord needs to be connected to the putatively corresponding nerve in the recipient body's spinal cord in order for the brain to control movement and receive sensory information. Finally, the risk of systematic neuropathic pain is high and as of 2017 had largely been unaddressed in research.
Of these challenges, dealing with blood supply and transplant rejection have been addressed in the field of transplant medicine generally, making transplantation of several types of organs fairly routine; however as of 2017 in a field as common as liver transplantation around a quarter of organs are rejected within the first year and overall mortality is still much higher than the general population. The challenge of grafting the nervous system remained in early stages of research as of 2017. In December 2017, a group of Chinese and Italian doctors claim that their first human head transplant on corpse was a success.
Wolfenstein 2: The New Colossus
It is revealed that the Da'At Yichud has perfected the technique to safely preserve and transplant a decapitated head to a new body thanks to Set Roth. The technique is first seen with Set Roth's pet that has the head of a cat and the body of a monkey, Shoshana. When B.J. was captured by Engel, Grace Walker develops an infiltration plan to rescue him. This results in Super Spesh's demise, and so Anya suggests that Set Roth conducts a head transplant to save B.J's. life like what he did to his pet Shoshana.
After B.J's. decaptation by Irene Engel, Set Roth manages to successfully oxygenate his head long enough in order to keep him alive and keeps his head in a jar of special preserving chemicals while he waits for a transplant. After Set Roth connects B.J.'s head to a bio-engineered Super Soldier's body stolen by Caroline using a special nerve-connecting halo, B.J. is revived and starts killing Nazis again for the greater good.