Expert answer

Dear Gina, Lots of psychiatric diagnoses generate controversy in the general public (e.g. attention deficit hyperactivity disorder, juvenile bipolar disorder), although they are noncontroversial in the mental health world. On the other hand, if you want to see mental health professionals spat with each other, ask a few of them what they think about dissociative identity disorder, the condition that used to be more colorfully known as multiple personality disorder.

Many biological psychiatrists who base their practices around medication management will tell you the condition doesn't exist, or that if it exists it is "iatrogenic," meaning it is caused by therapists training their patients to interpret their symptoms as if they have a whole set of distinct personalities. On the other hand, there are clinicians who specialize in the condition and they take the presence of multiple personalities so seriously that they will separate therapeutic meetings with each of a patient's "alters" (i.e. individual personalities). True believers will point to data that different personalities have different electroencephalogram tracings. Cynics will point out that actors can generate different EEG tracings when they switch characters.

As all psychiatrists, I have my opinion about dissociative disorders. I like to think it is a middle-of-the-road position, but I'll let you judge for yourself.

The dictionary defines dissociation as "an unexpected partial or complete disruption of the normal integration of a person's conscious or psychological functioning that cannot be easily explained by the person." I don't think anyone could doubt that this phenomenon exists. You can do the mental experiment. Think about a time when you were driving a car and suddenly realized you'd completely lost attention to the last number of miles, or that you'd missed a turn without even realizing it. That is dissociation -- you are doing something important and you lose track of the part of yourself that is doing it.

Like all other mental difficulties, dissociation runs a spectrum from normal to extremely pathological. In my clinical experience it is very common for traumatized and/or very mentally ill people to manifest high rates of dissociation. People who dissociate a lot have conscious experience that is like Swiss cheese: full of holes. But unlike sadness, anger or clear psychosis, it is not usually readily apparent, so it gets less attention than it should. People who suffer with this rarely complain about it, because almost by definition, their fragmented conscious awareness makes it very difficult for them to even notice that they are missing things and/or not aware. We also do not have good pharmacological interventions to reduce dissociation, so it has gotten less money behind it than have many other mental conditions.

There is no doubt that some people behave as if they have multiple personalities. And not all of them have been to therapists who have trained them to interpret their dissociative experiences in this way. Does this mean that dissociative identity disorder exists? In my opinion it depends on what we mean by "exists." Yes, dissociative identity disorder exists if by exists we mean there are people who complain of its symptoms and suffer its consequences. Do I think that some people have many biologically distinct entities packed into their heads? No. I think that some people dissociate so badly that either on their own or as a result of therapeutic experiences it becomes the case that the most convincing way for them to see their own experience is as if it is happening to multiple people.

If this sounds like an endorsement of the condition, it is in a qualified way. I am personally less sanguine, however, about treatments that proceed as if each of the separate personalities really exists concretely and then work to integrate them again. This is the most common therapeutic way to treat the disorder, but I have seen precious few successes and a lot of people made worse by this intervention. In all fairness, however, I used to work intensively on inpatient psychiatric wards and had to care for the train wrecks left behind when integrative therapies failed, so maybe I'm negatively biased.

Here is a final strange paradox regarding the question of whether dissociative identity disorder exists. Whether clinicians believe or disbelieve, they will all tell you that it is one of the most serious psychiatric difficulties. Patients who demonstrate dissociative identity disorder symptoms are all extremely ill in my experience. They have frequently undergone significant trauma, especially early in life. The chaos of their personalities and behavior often leave a tornado track in their wake, and they suffer tremendous emotional discomfort and anxiety. And, as I mentioned above, unlike mental conditions such as depression or psychosis, for which good -- although far from perfect -- treatments exist, there is very little evidence that any currently available interventions are of much help.