Dan Baumgardt: Neurosurgeon Sergio Canavero announced in 2015 that he might soon be able to perform the world’s first human head transplant procedure.
This would mean it would be possible to remove someone’s head and graft it onto someone else’s neck and shoulders. So far this has only been performed on cadavers and not on living people.
But what if you want to keep the face you already have? Or have you grown tired of the body you live in? Could it ever be possible to swap brains between bodies instead?
Emma Stone recently won her second Oscar for her role in the brilliant surreal comedy Poor Things. In the film, Stone’s character, Bella Baxter, receives a brain transplant from her surviving unborn child after she commits suicide. The operation is performed by experimental scientist Dr. Godwin Baxter (played by Willem Dafoe).
Anyone who has seen the movie will see Dr. Baxter removing the brain from the back of the skull and shelling it as easily as he would a pea from a pod.
For reasons I’ll explain later, this scene is not anatomically correct, but it does raise the question: how feasible is it to perform a brain transplant? What are the practical aspects of perhaps the most challenging operation ever conceived?
Challenge one: get in, get out
The living brain has the texture of soft-hardened scabies and is protected from damage by the skull. Despite being a tough nut to crack, the bone would probably prove to be the easiest structure to negotiate. Modern neurosurgical techniques use craniotomy saws to remove a piece of skull and access the underlying brain.
It is worth noting that not all neurosurgical operations reach the brain in this way. The pea-sized pituitary gland is located at the base of the brain, just behind one of the sinuses at the back of the nasal cavity. In this case, it makes sense to use the nose for pituitary surgery instead.
While the nose wouldn’t be big enough to insert a new brain, it could certainly serve as a route to remove one – albeit in pieces. During the mummification process, the ancient Egyptians, who considered the brain unimportant, removed pieces of it through the nasal passages.
Beyond the skull you reach the wrapping of the brain: three protective membranes or meninges. The first, the dura, is heavy. The second, the aptly named arachnoid, resembles a spider’s web, while pia, the third, is delicate and invisibly thin. It is these structures that become inflamed in meningitis.
These membranes provide stability and prevent the brain from flopping around. They also separate the viscera from the skull into compartments. The first creates a protective fluid cuff around the outside of the brain – think of pickles floating in a jar of vinegar. Known as cerebrospinal fluid (CSF), it is made of filtered blood and is colorless.
The meninges also create channels between the brain and skull. These are the routes by which both blood and CSF are returned from the head back to the heart.
When opening the skull and meninges there will be enough space to remove the brain. This would prove to be the simplest part of the operation.
Challenge two: connecting the circuits
Now it’s time to get the new brain involved. This is where things get complicated.
The brain receives sensory information from throughout the body and sends instructions back to it, causing the muscles to contract, the heartbeat, and the glands to secrete hormones.
Removing a brain requires cutting the 12 pairs of cranial nerves that come directly from it, and the spinal cord. Information enters and leaves the brain through all these structures. Do you see the difficulty?
Nerves don’t just come back together. Once you cut them off, they usually start to disintegrate and die, although some are more resistant to damage than others.
Research groups around the world are experimenting with promoting nerve cell regrowth after damage to prevent neurological symptoms. The ideas about this are numerous, but also include using chemicals or grafting cells that stimulate neuronal repair.
Researchers have also suggested that a special biological glue could be used to glue two severed ends of a severed nerve or spinal cord back together.
Removing the old brain will also require cutting the arteries that supply blood. This will also cut off critical oxygen and nutrition, which will also require recoupling.
Challenge three: the aftermath
The last, most uncertain period is the aftermath. And the list of speculations is endless. Will the subject regain consciousness? Will they be able to think? Movement? To breathe? How will the body respond to the new brain?
Most transplant operations require donors to match recipients because the body’s normal response to unknown tissues is to reject them. The immune system sends a cavalry of white blood cells and antibodies to attack and destroy, convinced that this new presence means damage.
Normally the brain is protected from this attack by another shield, the blood-brain barrier. If the donor brain is not properly reconstructed during surgery, it can be attacked.
It is equally important to consider how the brain will respond to its new home. In Poor Things, it was reported that Bella Baxter’s brain and body were “not quite in sync.”
But brains can learn to grow. So just as babies acquire an arsenal of thoughts, behaviors, skills, and abilities during infancy, a transplanted brain could do the same.
So brain transplantation currently remains the subject of science fiction and academy award-winning cinema. The feasibility according to basic anatomy and physiology makes the development of such a complex procedure unlikely. But will more time, tools, technologies, expertise and of course money ever make it viable? If Poor Things offers a glimpse into the ethics of brain swapping, it’s a frightening thought.
Dan Baumgardt, Senior Lecturer, School of Physiology, Pharmacology and Neuroscience, University of Bristol
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