Inter-identity amnesia and memory transfer in dissociative identity disorder: A systematic review with a meta-analysis

Individuals with dissociative identity disorder (DID) often report an inability to retrieve memories associated with other identities, termed inter-identity amnesia (IIA). Research investigating IIA has amassed, and interest surrounds whether objective deficits in retrieval mechanisms necessarily underlie the experience of IIA. This study conducted a systematic literature review with meta-analyses to examine current findings on IIA in DID. In particular, we explored whether DID patients' clinical reports of retrieval failure across identities were substantiated by controlled measures of memory. Nineteen empirical and four case studies informed the systematic review. The meta-analyses comprised twelve of the included studies. The systematic review findings suggested a degree of inter-identity memory transfer, a conclusion which was supported by two of the four meta-analyses. The remaining two meta-analyses evidenced patterns closer to IIA. Closer examination drew attention to methodological considerations that may limit definitive conclusions drawn from present studies. These include substantial heterogeneity between participants' scores which is masked by group statistics, a small and homogenous cumulative sample, limited research teams, and minimal domains of memory assessed. The paper urges a nuanced understanding of the phenomenon of IIA in light of current findings.