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What is dissociative identity disorder? Psychologist explains the reality behind the condition that Hollywood has turned into fantasy

Although it remains misrepresented and controversial, DID is a reality for people like folk legend Joan Baez –– and a testament to the power of the human mind, a Northeastern psychologist says.

A screen capture from the movie 'Split'.
M. Night Shyamalan’s “Split” is one of many movies that has taken dissociative identity disorder and heightened it into drama and horror. Universal Pictures

Watching movies and TV shows, it would be easy to think that dissociative identity disorder is something that exists only in the realm of thrillers and superhero stories. Previously known as multiple personality disorder, DID has been sensationalized to a fantastical degree in everything from “Sybil” to “Split” and Marvel’s “Moon Knight,” and it’s easy to see why.

Multiple personalities in one body: the idea lends itself to dramatic storytelling. But for some people, including folk legend Joan Baez, it’s not just material for Hollywood drama but a reality.

So, what is DID? William Sharp, an associate teaching professor of psychology at Northeastern University and a practicing therapist, says it is a severe personality disorder that happens when the brain, in response to trauma, figuratively splits, creating separate, autonomous personalities, or “alters.” 

Most people have different personalities; they’re just aware of them, Sharp says. We talk or behave differently around friends, family and work colleagues. It’s often referred to as code switching. Most people do it consciously or are at least aware of it. But with DID, those shifts are not conscious.

“The real mark for DID and MPD is that [the personalities] are operating autonomously,” Sharp says. “They kind of have a life of their own that some other personalities you possess didn’t have access to –– and some personalities did.”

Headshot of William Sharp.
Dissociative identity disorder often stems from a severe trauma that the brain is trying to protect the person from, says Northeastern University assistant teaching professor of psychology William Sharp. Photo by Alyssa Stone/Northeastern University

For those with DID, “it’s literally like a wall has come down and you have partitioned off that part of your mind,” he adds.

A person with DID can have multiple alters, some of whom might be aware of or even have relationships with each other. Alters can be different genders, ages or nationalities, which means the person’s vocal affect or accent might change when shifting between them. For example, one of Baez’ alters is a 12-year-old German boy. Certain skills the person might have, like playing the piano or carpentry, might also be split among different alters.

The real mark for DID and MPD is that [the personalities] are operating autonomously.

William Sharp, an associate teaching professor of psychology at Northeastern

In one of the most well-known cases of DID, Shirley Ardell Mason, known by the pseudonym Sybil, manifested 16 different personalities. Mason’s story was published in 1973 and later adapted into two different movies.

“There were some [alters] that were infantile, and she just crawled into a fetal position on Dr. [Cornelia] Wilbur’s floor,” Sharp says. “Then there were some little kids who liked performing for Dr. Wilbur and they played the piano or would sing and dance for her. And then there were the adult personalities, many of whom didn’t like some of the other personalities.”

Different alters fulfill specific roles. One might be a mother or a caretaker who provides stability, while another is a quick-tempered firecracker who manifests when danger arises.

DID remains a controversial topic in psychological and forensic circles, with some experts claiming it just doesn’t exist or that it results from therapists influencing a patient’s narrative or experience.

“They give examples that if you suggest to somebody that most people with multiple personalities have seven personalities, all of a sudden some people who have it will start generating seven personalities,” Sharp says. “It’s been discredited in that kind of way.”

Sharp admits it is likely very rare, but says it is just the brain’s way of trying to solve a problem.

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The trigger for DID and the creation of an alter is almost always intense trauma, usually at a young age and, at least in most cases chronicled so far, almost always involving some form of intense physical or sexual abuse. In Mason’s case, her DID stemmed from physical and sexual abuse she allegedly experienced from her mother.

“If I’m being abused, I’m going to create a personality that’s the personality that’s going to be abused and now I’m going to forget that it exists so that I can go on living a life,” Sharp says. “Certainly, there’s going to be problems because I’ve got moments of my life that I can’t remember, but at least I can go on living.”

“I do feel that it exists because I believe we have different personalities and I do believe that we can deny things that we don’t want to know,” Sharp adds. “The two mechanisms that would be part of having another personality that you can then not know about seems completely rational in my understanding of psychological dynamics.”

In that way, DID is the brain’s way of protecting us from a harsh, overwhelming reality. It’s why people with DID might not remember the initial trauma and sometimes experience a sense of lost time or even memory loss. In Baez’ case, she wasn’t diagnosed until much later in life, when she recovered memories of the abuse she experienced as a child at the hands of her father and others. 

“Whichever alter is in charge, [the mind] has created a narrative and a story to explain why you don’t know it’s three months later since the last time you checked in with yourself,” Sharp says. “It’s an attempt by the mind to say everything is fine, and we are motivated to believe it, so we do, even if to you and me it might be like, ‘What do you mean you can’t account for three months?’”

Like all of us, the various personalities we inhabit in our lives are all part of one cohesive whole. So, when it comes to treating DID, usually through therapy, the goal, Sharp says, is reintegration of a person’s alters. Baez says a few of her “entities,” as she calls them, are still present in her life; she just has more control.

“We all have different personalities,” Sharp says. “We probably have a lived experience of seamless transition from personality to personality. Somebody who had a less seamless or disruptive experience, once they get reintegrated, is probably still always going to recognize the shifts, shifts that you or I might ignore.”