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The long and controversial history of dissociative identity disorder

James McAvoy as Kevin Crumb. Photo/Supplied

James McAvoy’s screen portrayal of multiple personalities is energetic but not the real thing.

I have a confession. I’ve enjoyed all of M Night Shyamalan’s movies (apart from The Happening, which was just silly).

The latest is Glass. Without giving anything away that isn’t in the trailer, the film brings together characters from two previous movies, Unbreakable and Split. Both of those have psychological elements, with the theme that “superpowers” of the comic-book kind may be a kind of self-generated placebo effect: we may be super-strong, or particularly vulnerable to water, because we believe it’s true.

Glass has had a mixed reception, but James McAvoy’s performance as Kevin Crumb has won general approval. He steals both Glass and Split. In both, McAvoy’s body is home to numerous personalities, both male and female, aged nine and up, and McAvoy gives all of them everything he’s got.

Macro alias: ModuleRenderer

The notion of multiple personalities has a long history, recently characterised by controversy. Case studies apparently date back about 500 years, and long before that, the phenomenon may have been known as possession.

The condition’s symptoms are described in the 1952 first edition of the Diagnostic and Statistical Manual of Mental Disorders under the dissociated (multiple) personality label, alongside fugue, amnesia and sleepwalking. In 1968, it was classified as a dissociative subtype of “hysterical neurosis” (thanks, Freud) and then, in 1994, as multiple personality disorder. A disorder that appears, itself, to have multiple personalities now goes by the name of dissociative identity disorder, or DID for short.

The term “dissociate” means a detachment between something and something else. Most people have had a dissociative experience – when you feel like you’re not physically connected to your body, or maybe reality. People who feel this a lot, and are distressed by it, may be experiencing a clinically significant depersonalisation or derealisation disorder. Alternatively, if you experience amnesia about something extremely stressful or traumatic, then that may point to dissociative amnesia.

In the case of DID, the separation is between parts of one’s psychological self, one’s identity or identities. These are the “personalities”, and you can think of them as parts of a whole, but not really in conversation with each other – people have little recollection of what’s gone on when an “alter” has been in the spotlight.

DID has a controversial history. Some experts have argued that it’s not a real thing, that it’s like self-hypnosis, in which a highly suggestible person has convinced themselves that they have multiple personalities. There was a dramatic upswing in the diagnosis of DID after the 1973 publication of the book Sybil, and subsequent TV mini­series. There was also an increase in apparent demon possession after The Exorcist in 1973, leading critics to suggest that perhaps both demonic possession and DID are just made up.

A 2015 article in the Harvard Review of Psychiatry, however, systematically looks at what the authors call the “myths” of DID. Among other claims they contradict are the belief that DID is diagnosed mostly in North America (it’s not), that it’s vanishingly rare (as much as 1.5% of the population are affected) and that it’s just self-hypnosis.

This last is where the rubber hits the road. DID is theorised as a product of extreme trauma – a fracturing of identity as a form of self-defence. A review of all the studies on this question show that, sure, fantasy-proneness explains up to 2% of the variation in DID experience, but trauma explains more than a quarter.

The Harvard article concludes DID is a psychological reality. It’s certainly real for the people who experience it. Be warned, though, about taking McAvoy’s performance as a typical case study. It has roots in the science, but it is still a cinematic fiction.

This article was first published in the February 19, 2019 issue of the New Zealand Listener.