A critical test of the dual-representation account of PTSD

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Despite the high prevalence of post-traumatic stress disorder (PTSD) and its debilitating consequences, current psychological treatments are not effective for everyone. There is a clear need to uncover the psychological mechanisms that trigger persistent, intrusive fear memories. Our proposal tackles a rift in research, where a dominant theory of PTSD - the dual representation account - appears to clash with established cognitive-computational models of normal memory, and is challenged by discrepancies in its empirical evidence base. We propose to put the theory to two critical tests. The dual representation account makes two fundamental claims. First, that trauma makes it hard to bind emotional stimuli to their spatiotemporal context, and therefore, the associations between emotional aspects of the trauma and neutral elements of the same episode are weakened. Second, that intrusive memories arise from a separate mechanism than do voluntary memories of the same trauma content - a consequence of the first claim. We challenge the dual representation account by testing these two core claims using laboratory models of trauma, where participants are presented with pictures and film clips that depict aversive content, such as injury and death. Until now, laboratory tests of the first claim involved studies where participants were presented with emotional and neutral stimuli, and then tested for their memory for the association between these stimuli. The interpretation of such tests is complicated because the results depend not only on the critical binding of these stimuli during encoding, but also on subsequent effects of emotion during maintenance and retrieval. We will eliminate these potential confounds by targeting the encoding stage. We adapt a tried-and-true learning task to study the effect of emotion on associative binding without contaminating the measurement by subsequent memory processes. Laboratory evidence for the second claim is a single behavioural dissociation between voluntary and involuntary memory, where only the latter is decreased when participants actively engage in visuospatial manipulations following trauma exposure. Although this dissociation has been demonstrated multiple times, there are differences between the way that previous experiments measured voluntary and involuntary memory that could explain the discrepancy. We offer a more tightly controlled experimental design to confirm this dissociation. We then introduce a manipulation with potential to increase voluntary memory only. If successful, the visuospatial task and our new manipulation will amount to a double dissociation between voluntary and involuntary memory and thus offer stronger support for the dual representation account. To date, the dual-representation account has been mostly been described in words. This makes it difficult to understand the proposed cognitive-computational mechanisms precisely. Mathematical models increase the clarity of theories and make it possible to make, and test, quantitative predictions. As aforementioned, current descriptions of the dual representation account appear to disagree with mainstream theories of memory. We propose a way to adapt existing cognitive-computational models of neutral and emotional memory so that the revised model makes separate predictions for voluntary and involuntary memory. In summary, our proposal builds on the perspective of established models of memory, which appear to disagree with a dominant theory of PTSD. We use this perspective to test the dual-representation account empirically and develop a formal cognitive-computational model of this account. If our proposed model can simulate the empirical data we acquire, including the possible double dissociation we may observe between voluntary and involuntary memory, we will reconcile an important theoretical gap and thereby advance understanding of PTSD.