Until recently it was believed that people with Dissociative Identity Disorder have separate memory systems for each identity, divided by “impermeable amnesic barriers.” A new study suggests otherwise.
There’s a long list of horror films that involve people with multiple personalities. Perhaps most famous among them is Hitchcock’s “Psycho” from 1960, in which motel owner Norman Bates develops a split personality (Norman and “Mother”). Out of jealousy, “Mother” murders anyone Norman feels attracted to.
But violent people with a multiple personality disorder, currently known as the dissociative identity disorder (DID), aren’t just horror movie material. The link between the disorder and criminal acts is also obvious in real life. For example, a study that tracked 21 reported DID cases found that 19% of men and 7% of women were accused of murder. Therefore it isn’t that surprising that juries in court have relatively often been confronted with DID patients.
The first time DID was recognized as a mental disorder that could excuse criminal responsibility occurred in the case “State v Milligan” in 1978. The court declared serial rapist Billy Milligan insane due to lack of one integrated personality and therefore not culpable of the crimes he committed. Since this case, defendants have occasionally used DID as a basis for pleading not guilty by reason of insanity (NGRI).
Me, myself and I
But how does one become a DID patient? In most cases, people develop DID as a response to a traumatic experience. By developing multiple identities, including an identity that is not aware of the traumatic event, the person is able to ‘hide’ this experience. Individuals with DID can’t remember major or everyday events if they happened during the presence of a different identity. As a consequence, they forget appointments, things get lost or they fail to recognize even their own children as they’re unable to recall their birth.
Until now it was believed that people with DID have separate memory systems for each identity, divided by “impermeable amnesic barriers”. This would explain why patients are often unable to recall information related to another identity – such as the memory of a crime conducted by another identity.
But Clinical Psychologist Rafaële Huntjens of University of Groningen, the Netherlands, questioned if there really is no memory transfer across identities, even though a patient may report experiencing amnesia between identities. “That one identity does not report certain memories does not necessarily mean that these memories are truly inaccessible, or that the person is unable to recall it,” explains Huntjens.
Put it to the test
To test this hypothesis, Huntjens and her team selected nine patients diagnosed with and in treatment for DID. “The patients were asked to select two identities, one that was aware of a traumatic past and the other reporting no memories of the traumatic past. The first is called the trauma identity, the latter the amnesic identity,” explains Huntjens. “Another important criteria was the patients’ ability to switch between these two identities upon request, without spontaneous switches to or interference from other identities during the tasks.”
In the study, she assessed the recognition of autobiographical details in an amnesic identity. First of all, both identities of the subject were asked to complete 20 autobiographical information questions. “The questions ranged from the name of a best friend or favorite movie to their favorite food or favorite music of that identity,” explains Huntjens. Finally, the amnesic identity was also asked to complete the questions for the trauma identity. Several questions were answered incorrectly or left open by the amnesic identity. This indicated an inability to reproduce knowledge about the another identity.
I do know what you did
However, the opposite was demonstrated in a reaction test. Prior to the test, the amnesic identity was instructed to memorize some words. Then the reaction time on a sample of words was tested. When one of the memorized words appeared on the screen, the patient was instructed to quickly press the ‘yes’ button. With other, non-memorized words, the subject was supposed to quickly press the ‘no’ button.
The non-memorized words, however, were not all chosen randomly. Some of the words in this sample were in fact answers from the autobiographical questionnaire that had been provided by both the amnesic identity and the trauma identity. The words that were based on answers given by the trauma identity were allegedly unknown to the amnesic identity.
The results showed that the reaction time to press the ‘no’ button when dealing with an answer from the autobiographical questionnaire – given by themselves or by the trauma identity – was significantly slower than when seeing a random word.
An example might make this more easy to understand. Suppose one of the subjects, named Peter (the amnesic identity) has reported his favorite food is pizza. Then the trauma identity (Mark) answers the same question with “tomato soup.” When Peter is asked about Mark’s favorite dish, Peter doesn’t know the answer. But when the word “tomato soup” is (seeminlgy random) selected, Peter responds more slowly then when confronted with an actual random word. “That’s because the answer stands out: the individual recognizes the word as personally relevant,” explains the researcher, – “This recognition effect allows for the delay in response.”
According to Huntjens, their research proves that exchange of knowledge is possible between two identities: “one identity remembers words that are personally relevant for the other identity.” With this finding, the study also indicates that it’s unlikely that one identity is not aware of a crime committed by the other identity, says co-author Bruno Verschuere. And this could have consequences for future DID cases in court.
Until now, DID legal cases have had different outcomes, as legal and mental health professionals are divided on whether and to what extent DID justifies an acquittal for insanity. “If a defendant has DID, and the alter personalities are not aware of all the others, there are those who argue that it’s not fair to punish all of them,” says Stephen Morse, when interviewed for a New Scientists article. Morse is a specialisist in criminal and mental health law at the University of Pennsylvania.
Others argue that although a patient may have distinct personalities that control his or her behavior, this condition does not rule out criminal responsibility. In addition, the potential for malingering multiple personalities has presented another challenge in forensic assessments of offenders diagnosed with DID and claiming amnesia for violent crimes.
Now, as this study disproves the existence of amnesia in DID patients, this could put an end to the use of DID as a basis for pleading not guilty by reason of insanity. When all personalities – whether faked or real – are aware of a crime, one could say they’re all equally guilty.
Bourget, D, & Whitehurst, L (2007). Amnesia and Crime Journal of the American Academy of Psychiatry and the Law, 35 (4), 469-480.
Farrell, HM (2011). “Dissociative identity disorder: No excuse for criminal activity” (pdf). Current Psychiatry 10 (6): 33–40.
Huntjens RJ, Verschuere B, & McNally RJ (2011). Inter-identity autobiographical amnesia in patients with dissociative identity disorder. PloS one, 7 (7) PMID: 22815769