A critical review of methodological quality in functional neuroimaging studies on dissociative identity disorder.

Background: Dissociative identity disorder remains contested. The debate hinges on whether memories carry over between identity states and whether those states are truly distinct, but most evidence rests on self report rather than direct memory tests. Neuroimaging has been advanced as an indirect, non self-report approach by scanning individuals with DID in different identity states and comparing them with simulators or other groups. Objective: To evaluate how studies that scan people with DID in more than one identity state inform the core memory claims of DID, by assessing their methodological quality. Methods: Systematically reviewing studies from the past 40 years, quality was assessed using GRADE criteria and the Newcastle-Ottawa scale. Results: Of the nine studies reviewed, many lacked specific aims and only one stated clear hypotheses throughout. The results further indicated several concerns related to diagnostic comorbidity, and absence of clinical comparisons, reverse inference, and post hoc reasoning. Conclusions: On current evidence, functional imaging across identity states does not support firm claims about identity fragmentation or inter identity amnesia, nor does it decide between trauma based and sociocognitive accounts. Methodological refinement and direct tests of memory transfer are needed for progress.