Patients with Dissociative Identity Disorder do remember separate identities

People with Dissociative Identity Disorder (DID) are able to exchange information among their separate identities. This has been revealed by experiments conducted by NWO researcher Rafaele Huntjens of the University of Groningen. Although the investigated patients said that they remembered nothing of other identities, objective data reveal that this is in fact the case. The research results have important implications for the treatment and diagnosis of the disorder. The clinical psychologist published her research on 18 July in the Open Access journal PLoS ONE.

A Dissociative Identity Disorder (DID) can emerge as a reaction to a traumatic experience. By developing several identities, including one that is not aware of the traumatic event, a person can ‘lock away’ this experience. People with DID cannot remember important or everyday events if they occurred while a different identity was present. They can forget meetings, lose possessions or even not recognize their own children because they cannot remember their birth at that moment. For years it has been assumed that people with DID have separate memory systems for each identity. However, recent research shows that this is not the case – the patients definitely have knowledge about a different identity, even if they do not experience it as such.

During her research, Huntjens tested the autobiographical knowledge identities had of a different identity. First, the test subjects had to answer twenty questions about their preferences or life histories while they were in two different personalities. ‘The questions ranged from the name of their best friend or favourite film to the favourite food or music of that personality’, Huntjens explains. ‘We then asked the first identity to answer the same questions for the second identity.’ Several questions were usually incorrectly answered by the first personality, or left open. That appeared to indicate an inability to reproduce knowledge about a different identity.

Reaction time crucial

However, the opposite was demonstrated during a reaction test. In advance, one identity was given instructions to learn several random words off by heart. If one of those words appeared on the screen, they were to quickly press the ‘yes’ button. For all the other words, the test subjects had to push the ‘no’ button as quickly as possible. However, the other words were not all made up. Some of them were the answers filled in by the first personality during the autobiographical questionnaire from the first test. The reaction test also contained the correct answers from the second personality, which the first personality had no knowledge of.

The experiment revealed that the reaction time when pressing the ‘no’ button for one of the non-learned words was significantly slower when it was their own answer from the first test or one of the answers of the other identity from the first test than when it was a made-up answer. ‘This is because the answer stood out – the individual recognized that the word had a personal relevance’, explains the researcher. ‘That recognition effect results in a slower reaction’. According to the clinical psychologist, this is objective confirmation that there is knowledge exchange between the two identities – one of the identities remembers words that are personally relevant for the other identity.

Adapting treatment

Thus far, memory loss was the most important element that set DID apart from Post-Traumatic Stress Disorder (PTSD). According to Huntjens, this differentiating element is now void. ‘Therapists can now consider whether or not to give DID patients the quicker, proven effective treatment that is given to PTSD patients’, says Huntjens. Future research should show whether this approach is indeed more efficient for DID patients. There are also implications for forensic research – perpetrators with DID do indeed have knowledge of the crimes they committed in a different identity.

Rafaele Huntjens's research was supported by a Veni grant from NWO. The research was conducted in cooperation with the universities of Harvard and Amsterdam. The article can be read online at http://dx.plos.org/10.1371/journal.pone.0040580.