Severance on Apple TV+ and the neuroscience of split-brain minds

Severance - the Apple TV+ drama that pictures a society in which someone’s working life and private life are surgically walled off from one another - is set to return for a second series.

The premise is deliberately extreme, but it brushes up against genuine questions from neuroscience. Is it actually possible for surgery to divide a single mind into two?

Remarkably, cases that look a little like this have been documented for decades. So-called "split-brain" patients have been treated since the 1940s.

Severance, "split-brain" surgery and two minds in one brain

In an effort to reduce severe epileptic seizures, surgeons cut the connections between the brain’s left and right hemispheres. Operations along these lines are still carried out today.

Subsequent studies of people who had undergone this procedure found something striking: once separated, the two hemispheres can handle information in parallel, each largely on its own. That finding leads to an unsettling thought - that the operation might, in effect, produce two distinct minds inhabiting a single brain.

Series one of Severance dramatised a tug-of-war between Helly R (Britt Lower) and her two versions: her "innie" (the part that retains her working experiences) and her "outie" (the part that exists beyond work). Real split-brain patients can show hints of a comparable push-and-pull between hemispheres.

In ordinary conversation with a split-brain patient, you are typically engaging the left hemisphere, because it governs speech. Some people, though, can relay what the right hemisphere “knows” in other ways - for instance by writing, or by arranging Scrabble tiles.

In one well-known example, a young patient was asked what career he wanted later in life. His left hemisphere opted for an office role producing technical drawings. His right hemisphere, by contrast, laid out letters that spelled "automobile racer".

Split-brain patients have also described "alien hand syndrome", in which one hand seems to act independently, as if it has a will of its own. Observations like these are consistent with the idea that two separate conscious “individuals” may coexist within one brain - and that their aims can sometimes clash.

Neil’s case: memory that exists outside awareness

Even so, Severance differs from split-brain surgery in an important respect: both the "innie" and the "outie" can speak. That alone implies that the show’s fictional “severance procedure” would have to involve something more intricate than simply separating the hemispheres - more like a selective partitioning of networks.

A real-world illustration of complex separation of function appears in a 1994 case report about Neil, a teenage boy who developed multiple difficulties after a pineal gland tumour.

Among his problems was an unusual kind of amnesia. Neil could not bring to mind what had happened during his day, nor could he describe what he had learned at school. He also lost the ability to read, despite still being able to write, and he could no longer name objects even though he could draw them.

What made the case all the more surprising was that Neil nevertheless managed to continue with his schooling. Researchers wanted to understand how he could complete classwork while apparently unable to remember what he was studying.

They questioned him about a novel he was reading at school, Cider with Rosie by Laurie Lee. In spoken conversation, Neil could not recall anything about the book - he could not even produce the title.

However, when a researcher asked him to write down everything he could remember about it, he produced: "Bloodshot Geranium windows Cider with Rosie Dranium smell of damp peppar [sic] and mushroom growth" - a set of words linked to the novel.

Because Neil could not read, he then had to ask: "What did I write?"

Neil could also write down other recollections that were believed to be inaccessible, including an encounter in hospital with a man who had gangrene. Each time, Neil did not recognise the memory as his own until he had written it and then heard it read aloud. His case is extraordinary, and it indicates that detailed memories can exist without being available to conscious awareness.

Severance offers a fictional parallel. Irving’s (John Turturro) outie is able to reach into his innie’s workplace memories through painting: he repeatedly depicts the long corridors of the Severed floor (where his innie works) despite having no conscious recollection of them.

On that view, the show’s procedure might be imagined as blocking conscious access to memory in a way reminiscent of what seemed to happen for Neil.

The role of the hippocampus

So which brain regions would be central to a severance-like procedure in a television world? The area most closely linked with remembering the day’s events is the hippocampus - and, intriguingly, the hippocampus is also crucial for representing space.

That one and the same neural structure helps you remember, for example, that a new colleague joined your team today and also supports a mental map of the office layout makes the hippocampus an appealing candidate target for the show’s fictional intervention.

In Severance, the transition between "innie" and "outie" happens at the edge of the workplace - the lift doors. This resembles the "doorway effect": the tendency for walking through a doorway to make you forget what you were just thinking about.

The hippocampus helps parcel our ongoing experience into episodes that can be retrieved later. Moving into a new space is a cue that a fresh episode has begun, which can increase forgetting for information that straddles the boundary between episodes. In everyday life, however, the effect is mild.

You might wander into the kitchen and draw a blank about what you meant to do, but you do not suddenly forget that you have children - unlike the dramatic reset depicted by the show’s severance procedure.

It is therefore tempting to imagine that, in Severance, the hippocampus’ sensitivity to spatial boundaries is what sets off the "innie"/"outie" switch.

Why a simple hippocampus ‘snip’ would not match Severance

There are, unfortunately, two major problems with the idea that severance could be achieved by a straightforward cut involving the hippocampus.

First, Severance does not merely split episodic and spatial memory. The workers retain extensive semantic knowledge - facts about Lumon, the company they work for, and about its founder, for instance - that their outies cannot access.

They also acquire emotional memories tied to the incentives for productivity and the punishments they experience in the break room. Those kinds of memory depend on much more than the hippocampus. And the hippocampus itself forms part of a brain-wide episodic memory network that becomes active when episodic memories are retrieved.

Second, memory cannot be cleanly separated from everything else. It is tightly interwoven with perception, attention, language and many other functions. Human memory is far too complex to be neatly divided into two wholly independent halves - but, as Severance demonstrates, it is compelling to explore what the limits might be.

Rachael Elward, Senior Lecturer, Neuroscience and Neuropsychology, London South Bank University and Lauren Ford, PhD candidate in cognitive neuroscience, London South Bank University

This article is republished from The Conversation under a Creative Commons licence. Read the original article.