Comment on Otgaar et al.: The neuroscience of dissociative amnesia and repressed memory: Premature conclusions and unanswered questions

Otgaar and colleagues admirably highlight the strengths and weaknesses of past research, while proposing strategies for studying ‘psychogenic amnesia’ and its related concepts, along with their neural correlates. They argue convincingly for redefining psychogenic amnesia as ‘amnesia of uncertain etiology’, considering various potential causes, like unclear origins or feigned memory loss (Mazzoni, 2019; Vannucci et al., 2015). The prevalence of feigned dissociative disorders as a form of malingering and symptom exaggeration, as noted by Mittenberg et al. (2002), underscores the importance of investigating such factors in research contexts.

A central point of Otgaar's contribution, which we extend in this commentary, is the statistical concept of correlation. As already stated elsewhere (e.g. Convertino et al., 2022), the concept of correlation is quite different from the concept of causation, just as the concept of statistical correlation is remote from the concept of statistical causation. Despite many advances in data sciences for the development of robust causal inferential strategies (Peters et al., 2017), not all neuroscientific studies in the literature adopt these options, amplifying biases especially at the data interpretation stage, which in turn distort results and lead to erroneous conclusions.

Moreover, sometimes readers may inadvertently misunderstand, interpreting honestly reported data of associations as evidence of causation. In the clinical setting, also due to problematic overlapping of concepts and debates (e.g. definition and characteristics of ‘repressed memory’ vs. ‘criteria/diagnosis of dissociative amnesia’; see Battista et al., 2023; Mangiulli et al., 2022), professionals fall for the easy conceptual fallacy (Fukuzako et al., 1999) of inferring a cause, for example ‘traumatic experiences’, from the observation in a patient of DSM-5 symptoms that merely correlate with trauma.

In cognitive neuroscience, scientists are aware of these limitations: in fact, the presence of a relationship between the observed variable (e.g. reporting having suffered a trauma) and the measured outcome (e.g. dissociative amnesia) is not sufficient in determining the causal relationship between two phenomena. Only counterfactual data derived from direct manipulation can suggest causation. In this sense, major advances have been obtained through the implementation of invasive and non-invasive brain stimulation techniques capable of experimentally manipulating brain functioning and measuring the consequent behavioural outcomes. As rightly pointed out by Otgaar and colleagues, functional and/or structural brain imaging studies investigating amnesia of uncertain aetiology are unable to reach conclusions with causal value, lacking counterfactual evidence.

Despite these challenges, the neuroscientific literature has made significant efforts trying to overcome the limitations of (correlational) studies. For instance, Lyu et al. (2023) conducted an innovative study where they successfully induced dissociative symptoms of the body self in nine patients through electrode implantation in specific brain regions. By employing neuroimaging, intracranial recordings and direct cortical stimulation, this study represents a substantial step towards unravelling with a correct methodology amnesia-related phenomena.

Conclusively, we agree with Otgaar and colleagues on the need of critically examining (neuroscientific) research on extreme forgetting, applying transparent research practices and being aware of the responsibility in reporting and discussing findings to the scientific community.