THIS ARTICLE IS reissued from The Conversation under s Creative Commons License.

Separationwhich imagines a world where a person’s work and personal lives are surgically separated, returns Friday for its long-awaited second season. While the concept of this gripping piece of science fiction is far-fetched, it touches on a question that neuroscience has been trying to answer for decades: Can one’s mind really be split in two?

Remarkably, “split brain” patients have existed since the 1940s. To control epilepsy symptoms, these patients underwent surgery to separate the left and right hemispheres. Similar operations still take place today.

Later research on this type of surgery showed that the separated hemispheres of split brain patients can process information independently. This raises the uncomfortable possibility that the procedure creates two separate minds residing in one brain.

In season one of SeparationHelly R (Britt Lower) experienced a conflict between her “innie” (the side of her mind that remembered her work life) and her “outie” (the side outside of work). Similarly, there is evidence of a conflict between the two hemispheres of actual split-brain patients.

When you talk to split brain patients, you are usually communicating with the left hemisphere of the brain, which controls speech. However, some patients can communicate from their right hemisphere by, for example, writing or arranging Scrabble letters.

In one study, a young patient was asked what job he would like to have in the future. His left hemisphere chose an office job making technical drawings. However, his right hemisphere arranged letters to spell “car racer”.

Split brain patients have also reported “alien hand syndrome” where one of their hands wants to move on its own. These observations suggest that two separate conscious “people” can coexist in one brain and have conflicting goals.

In Separationhowever, both the innie and the outie have access to speech. This is one indicator that the fictitious “separation procedure” must involve a more complex separation of the brain’s networks.

An example of a complex separation of function was described in the case report of Neil, in 1994. Neil was a teenage boy who had a number of problems following a pineal gland tumor. One of these problems was a rare form of amnesia. This meant that Neil could not remember the events of his day or report what he had learned at school. He also became unable to read, although he could write, and he could not name objects, although he could draw them.

Surprisingly, Neil was able to keep up with his education. Researchers became interested in how he was able to complete his schoolwork despite having no memory of what he learned. They asked him about a novel he studied at school, Cider With Rosie by Laurie Lee. In conversation, Neil could remember nothing about the book—not even the title. But when a researcher asked Neil to write down everything he could remember about the book, he wrote “Bloodshot Geranium windows Cider with Rosie Dranium smell of damp pepper”. [sic] and mushroom growth”—all words related to the novel. Since Neil could not read, he had to ask the researcher, “What did I write?”