Högskolan i Skövde

Dissociative Identity Disorder (DID) is a complex psychiatric disorder characterized by disruptions in identity, memory, and consciousness. Previous research suggests that memory functioning in DID may vary depending on the active identity state, particularly between Neutral Identity States (NIS) and Trauma Identity States (TIS). The aim of this systematic review was to investigate whether autobiographical memory and working memory are processed differently in NIS and TIS and to examine if memory functioning in DID is state-dependent. A systematic literature search was conducted in Web of Science and Medline EBSCO following PRISMA guidelines. Studies were included if they examined individuals diagnosed with DID using neuroimaging methods such as functional magnetic resonance imaging (fMRI), positron emission tomography (PET), electroencephalography (EEG) or event-related potentials (ERP). Four studies met the inclusion criteria, with a total of 148 participants being included in the review. The findings demonstrated consistent differences between NIS and TIS in both memory processing and cognitive performance. Trauma identity states were associated with reduced working memory performance, slower reaction times, increased omission errors, and stronger responses to trauma-related material. In contrast, Neutral Identity States showed relatively preserved working memory functioning, better cognitive performance, and greater detachment response from trauma-related stimuli. The reviewed studies also indicated that autobiographical memory retrieval differed between identity states. Furthermore, behavioral and neurophysiological evidence suggested that memories may remain accessible at an implicit level despite subjective reports of amnesia between identities. The results support the view that memory functioning in DID is state-dependent and that dissociative amnesia may reflect impaired conscious access to memories rather than complete memory loss. These findings contribute to a better understanding of memory processes in DID.