How Realistic Is the Severance Procedure? Brain Surgeons Have Some Thoughts

Severance, the extremely popular Apple TV+ series about office workers who undergo brain surgery so that their home selves have no knowledge or memory of their working selves, and vice versa, is often described as science fiction. That’s a reasonable characterization, since the simple outpatient brain surgery that splits a person between an “innie” at the office and an “outie” at home isn’t available to the rest of us.

But while the science the show depicts goes well beyond anything that’s currently possible, many brain specialists and neurosurgeons are still fans. “I love Severance because it brings up such an important function that the brain takes care of without our even realizing it,” which is establishing our identity simply by being aware of ourselves, our experiences, and our own inner drama, says Dr. Jordina Rincon-Torroella, assistant professor of neurosurgery at Johns Hopkins University.

[time-brightcove not-tgx=”true”]

We asked Rincon-Torroella and other brainiacs who watch or are familiar with Severance their thoughts about how brain surgery and all things neuro are depicted on the show.

A clean—and pretty believable—depiction of brain surgery

The first step in changing the brain is being able to physically get at the brain, and it’s here that Severance’s sci-fi first spills over into sci-fact. Although the term “brain surgery” might call to mind a sawed-open skull exposing a pink, pulsating mass, the surgery that the subjects undergo involves drilling a small hole—about the size of a dime—in the posterior crown of the skull and inserting a small chip in the brain tissue underneath. The procedure is quick, simple and, as these things go, relatively bloodless.

That kind of minimally invasive surgery is not at all outside of the realm of what’s possible today. “We can treat tumors or areas of the brain that cause epilepsy by drilling a small bore hole in the skull and inserting a laser probe under MRI visualization,” says Dr. Hoomin Azmi, director of functional and restorative neurosurgery at Hackensack University Medical Center. “We can then watch the tumor being burnt away on the MRI.”

The surgeons in Severance use no such sophisticated imaging, simply peering into the brain and hand-placing the chip—and getting it right every time. ”In terms of surgery [in the show], it’s obviously a bit of science fiction,” says Azmi.

Some types of brain surgery don’t require opening the skull at all. Aneurysms—or bubbles in the wall of an artery—can be treated by threading a probe from an artery in the groin or the wrist up to the brain and closing off the affected area with a coil or a stent.

“This has drastically changed outcomes and complications for patients,” says Azmi. “I think the days of doing brain surgery in the office are still far from us. But the trajectory of less invasive and safer brain surgery has been going on for several years.”

Some procedures are less invasive still, making no physical contact with brain tissue at all. Transcranial magnetic stimulation (TMS) applies magnetic pulses to the scalp to treat symptoms of major depression. Focused ultrasound can be beamed through the skull and ablate, or surgically remove, tumors without any reliance on a drill or a scalpel. “It’s also helping us ablate centers of the brain in patients who have essential tremor, or a tremor that cannot otherwise be controlled,” says Rincon-Torroella.

A less-realistic depiction of memory control

Severance takes more scientific liberties when it comes to the part of the brain in which the memory-manipulating chip is implanted. That region in the crown of the head is known as the parietal lobe, and while the parietal does a lot of jobs—especially processing sensory information such as touch, temperature, pain, and spatial awareness—it is not where memory lives.

The ability to form short-term memories is governed by the hippocampi, two structures which lie deep within both brain hemispheres. But a host of other parts of the brain—including the fornix, basal ganglia, thalamus, amygdala, caudate nucleus, and prefrontal cortex—also play a role in consolidating and storing longer term memories. That’s an awful lot of neural real estate for a chip implanted in the parietal to cover.

At a minimum, says Rincon-Torroella, a memory-altering chip would have to target the hippocampi, for their memory-forming function, and the amygdala, which governs emotions. “Memory and emotions are so attached to each other,” she says. “These would be the areas that I would attempt to approach if we would consider the idea of whether we could split an identity.”

But turning off key brain regions might not be reversible. “You could, for example, knock out short-term memory if you turned off or severed both hippocampi and the fornices,” says Dr. Daniel Orringer, associate professor of neurosurgery at NYU Langone Health. “People would not be able to create these memories, but that’s a destructive thing.”

Azmi does not believe the memory control Severance depicts is entirely out of the realm of possibility—just not in the foreseeable future. “We’ll probably reach the day that perhaps we can select memories and deselect other memories,” he says. “I think that’s many years away.”

Even if it were possible to toggle back and forth between on and off in two or three brain regions, that would not, by itself, be sufficient to create the dual identities the characters in Severance exhibit. “Memory is so complex and involves many different areas of the brain,” says Dr. Howard Riina, vice chair of the department of neurosurgery at NYU Langone Health. “It’s also hemispheric; there are components of memory on the left side of the brain and the right side of the brain. A chip would have to have some kind of global effect from the one area where it’s implanted.”

The potential of brain chips

That may not be possible with existing technology, but implanted brain chips that work locally—in a single targeted region of the brain—are already in development. California-based Neuralink, Elon Musk’s company, is working to create computer chips that could be implanted in the brain and allow quadriplegics to control computers and other devices with their thoughts. BrainGate, a consortium of neurologists, engineers, computer scientists, and more, looks to implant not chips but electrodes in the brain, similarly allowing people with paralysis, ALS, or brainstem stroke to manipulate their environments, sometimes simply by thinking about using their paralyzed arm and hand to manipulate a computer cursor. Deep brain stimulation—in which electrodes connected to a pacemaker-like device are threaded to targeted regions of the brain—is already being used to control tremors related to Parkinson’s disease, as well as epilepsy, Tourette’s syndrome, dystonia, and more.

“You have people that have injuries, they have strokes, they have trauma, they have cerebral palsy,” says Riina. “You might be able to augment these people, or even use different parts of the brain to compensate for the damaged area.”

Augmenting, inhibiting, or otherwise manipulating consciousness and identity, including memory, would be a much heavier lift than treating a lesion, injury, or disease in an isolated region of the brain, and while Severance makes for good TV, it does not on the whole invoke rational science—at least not in the remotely foreseeable future.

“The brain is staggeringly complex in terms of its connectivity,” says Orringer. “It also varies from person to person. So everybody’s network is laid down in a little bit of a different way. The idea that you could turn off a subset of memories and still have memory function? That seems a little bit implausible.”