Patients with disassociative identity disorder do remember separate identity

A disassociative identity disorder (DID) can occur in response to a traumatic experience. By developing several identities, including an identity that is not aware of the traumatic event, a person can ‘hide away’ this experience. People with DID can no longer remember important or everyday events that happened during the presence of the other identity. For example, they forget appointments, lose things, or even fail to recognise their own children because at that moment they cannot remember their birth. Up until now it had been assumed for many years that people with DID have separate memory systems for each identity. Recent research, however, has revealed that this is not the case: the patients definitely know something about another identity even if their experience is otherwise.

In her research Huntjens tested how well an identity knew the autobiographical knowledge of another identity. First of all the study subjects had to answer twenty questions about their preferences and life history when in one personality and subsequently in another. 'These questions varied from the name of the best friend or favourite film to the favourite food or music of that personality,' says Huntjens. 'After that we asked the first identity to answer the same questions again but then for the second identity.' During that exercise several questions were incorrectly answered or not answered at all by the first personality. That seemed to indicate an inability to reproduce knowledge about the other identity.

Response time crucial

However the opposite result was demonstrated during a response time test. Prior to the test, one identity had received the instruction to memorise random words. If that word subsequently appeared on the screen then they had to press the 'yes' button as quickly as possible. For every other word the study subjects had to press the 'no' button as quickly as possible. These other words, however, were not all randomly chosen. They also included answers that the first personality had completed during the autobiographical questionnaire in the first test. The response time test also contained the correct answers from the second personality that the first personality knew nothing about.

This experiment revealed that the response time to press the 'no' button was significantly slower when an answer from the first test of this identity or an answer from the first test of the other identity appeared on the screen than if made-up answerswere seen. 'That is because the answer stands out: the individual recognises the word as personally relevant,' explains Huntjens. 'That recognition effect gives rise to the delayed response.' According to the clinical psychologist this objectively demonstrates that knowledge exchange takes place between the two identities: one identity remembers words that were personally relevant for the other identity.

Modify the treatment

Memory loss has always been the most important factor that distinguished DID from a post-traumatic stress disorder (PTSD). However, this distinction is now obsolete according to Huntjens. 'Therapists can therefore consider giving DID patients the faster and demonstrably effective treatment PTSD patients currently receive,' she says. Future research must demonstrate whether this approach is indeed more efficient for DID patients. There are also implications for forensic research: a perpetrator with DID is therefore clearly aware of criminal actions that he or she committed in a different identity.

Rafaele Huntjens realised her research with a Veni grant from NWO. The research was carried out in collaboration with Harvard University and the University of Amsterdam.

More information: dx.plos.org/10.137… pone.0040580

Journal reference: PLoS ONE

Provided by Netherlands Organisation for Scientific Research (NWO)