Psychology 101: Intro to Psychology

There are times when the human brain can actually separate its different parts, sometimes as a defense mechanism. These are known as dissociative disorders. This lesson takes a closer look at these kinds of disorders and how they impact the mind.

What does someone with multiple personalities have in common with someone with amnesia? The two conditions may seem very different; one has patients with distinct personalities living in the same brain, while the other causes patients to forget pieces of their lives. Yet both are categorized as dissociative disorders, which is a general term for disorders that cause disturbances in consciousness, memory, identity or perception. So what's the common denominator between multiple personalities and temporarily forgetting your name and birthday?

Essentially, dissociative disorders are caused by a given part of the mind 'dissociating' itself from another part. This means one part of the mind basically forgets or ignores another part. In dissociative amnesia - different than the kind of amnesia caused by injury or illness - the mind basically loses track of the part of itself that stores important personal information. You've probably had the experience - maybe on a history test - of being totally unable to remember something important. But patients with amnesia often don't even recognize that the lost information is missing - and they lose much more than simply what day the Civil War began or where their keys are.

There are two main types of dissociative amnesia. Retrograde amnesia is when a patient forgets their past, up to a certain point, but is able to form new memories. This kind of patient would basically be starting a new life as a new person, functioning in most ways except totally unable to remember the past. Retrograde amnesia, which literally means moving backward, plays an important role in the movie 'The Bourne Identity,' in which Matt Damon's character wakes up on a boat with no idea who he is and no memory of his military training. Anterograde amnesia is the opposite of retrograde, and literally means forward moving. Patients with anterograde amnesia can't form new memories, but do remember everything before the amnesia set in. This is true of Drew Barrymore's character in '50 First Dates,' who quite literally goes on 50 dates with Adam Sandler that seem to her as if they're the first because she cannot form new memories. Though she knows who she is and remembers her past and her childhood, she wakes up each morning thinking she and Adam Sandler haven't met.

Different from 'dissociative amnesia,' but sharing the feature of memory-loss, is a dissociative fugue. Also known as a fugue state, it's when a patient completely forgets their personal identity temporarily - usually for a few hours, or for a few days at most. People in fugue states will often wander around, and even attempt to set up new identities for themselves. A man in an extended fugue state might go apply for a new job, go on a date with a woman, find himself an apartment - all while his wife and children are frantically looking for him. Fugue states are usually set off by environmental stressors, like a traumatic event. Once the patient remembers who they are, memories of what happened during the fugue state are totally wiped; it's like it happened to somebody else.

It is in this sense that split or multiple personalities is related to the other dissociative disorders. Imagine you speak two languages, and think about what it's like to switch fluidly from one language to another. Now imagine that each language is attached to a specific personality; this is stranger, but some bilingual people do say that they think and behave slightly differently in the different languages they speak. Now imagine that these personalities can't access each other's memories and know nothing about each other; that's probably not something you have experience with, but it's what patients with multiple personalities experience. A TV show called 'United States of Tara' explores this phenomenon; a middle-aged mother of two transitions into other personalities when under stress, including 'Alice,' a 1950s housewife, 'Buck,' a (male) Vietnam War veteran, and 'T,' a teenage girl.

Split personalities are formally known as dissociative identity disorder. Patients report that experiences undertaken by one personality are not remembered by the other, hidden away in another part of the mind in a similar way as the events of a fugue state. Some patients' multiple personalities actually exhibit different patterns of electrical activity in the brain, as if they were truly different people. Others have patterns that are the same, so it is unclear whether this is truly a marker of the disorder. Split personalities are thought to be caused by trauma during childhood, by stress or insufficient nurturing. Many patients even report physical or sexual abuse during childhood.

Dissociative disorders cause the brain to inappropriately segregate itself in a way to cause amnesia or the experience of multiple personalities. This is usually triggered by trauma of some kind, perhaps as an effort to hide or bury a memory. These disorders are still not entirely understood, and sometimes their diagnosis is controversial.