حافظه کاذب خنثی و مرتبط با تروما در اختلال استرس پس از سانحه ناشی از جنگ

Recent models of cognition in Posttraumatic Stress Disorder (PTSD) predict that trauma-related, but not neutral, processing should be differentially affected in these patients, compared to trauma-exposed controls. This study compared a group of 50 patients with PTSD related to the war in Bosnia and a group of 50 controls without PTSD but exposed to trauma from the war, using the DRM method to induce false memories for war-related and neutral critical lures. While the groups were equally susceptible to neutral critical lures, the PTSD group mistakenly recalled more war-related lures. Both false and correct recall were related more to depression than to self-rated trauma. Implications for accounts of false memories in terms of source-monitoring are discussed.

As a result of exposure to severe trauma, some people develop a relatively stable, potentially chronic disorder called Posttraumatic Stress Disorder (PTSD). Over recent years, several models of cognitive functioning in PTSD have been articulated (Brewin, 2001, Brewin et al., 1996 and Ehlers and Clark, 2000). In the latter model, for example, Ehlers and Clark (2000) propose a set of cognitive dynamics that lead to the maintenance of persistent PTSD, involving the use of strategies with which the person attempts to keep unpleasant mental intrusions to a minimum, and that paradoxically make their elimination more difficult. In these models, trauma exposure per se is not enough to produce and maintain PTSD: particular cognitive patterns that only arise in some trauma-exposed people are necessary to produce that. Furthermore, cognitive differences between people with PTSD and trauma-exposed people without PTSD will be amplified when the content of the cognitions is trauma-related. That is, PTSD is assumed to have effects on cognitions thematically related to the traumatising event. Therefore, a general prediction of Ehlers and Clark’s framework is that trauma-related cognition should be particularly impaired for PTSD patients. From studies of PTSD and memory function, there is ample evidence of a deficit in short- and long-term memory for emotionally neutral material in PTSD patients versus trauma-exposed controls (for a review, see Buckley, Blanchard, & Neill, 2000). There are, however, fewer studies that have used trauma-related materials with PTSD patients in tasks tapping semantic memory. Golier, Yehuda, Lupien, and Harvey (2003) showed that although survivors of the Holocaust with PTSD recalled fewer paired associates than Holocaust survivors without PTSD, regardless of whether they were trauma-related or emotionally neutral, the disadvantage was smaller for the trauma-related pairs, which can be seen as consistent with Ehlers and Clark’s prediction. One of the positive outcomes of the “greatest psychological controversy of the 1990s” (Lindsay & Read, 2001), the so-called memory wars, has been the development and widespread use of paradigms demonstrated to get false memories under laboratory control. Roediger and McDermott (1995) revived a paradigm by Deese (1959) wherein participants try to remember lists of words, with the members of each list being associatively related to a non-presented target word, the so-called “critical lure”. For example, a standardized list with the non-presented critical lure “sleep”, begins “bed, rest, awake, tired” (Stadler, Roediger, & McDermott, 1999). On both recognition and free recall tasks, participants mistakenly claim that the critical lure was presented in the study list, often at rates comparable to that of words that were actually presented. Moreover, when asked for a rating of how sure they were that the word was actually presented, it is evident that on a variety of different measures (Remember/Know, confidence), “memory” for the non-event is compelling. This paradigm, often called the DRM paradigm, is thus a productive way of eliciting false memories in the laboratory context. False memories in this paradigm are often seen as source-monitoring errors (see e.g., Brédart, 2000 and Schacter et al., 1996). The presentation of a series of words all thematically related to the same lure word conjures it up in the participant’s mind. Then, in the recall test, if the participant recalls the lure word but fails to correctly classify it as self-generated, rather than actually presented, a false memory occurs. There is reason to believe that PTSD patients may have a particular impairment in source-monitoring, and thus a tendency towards higher production of false memories, due to an association between the disorder and dissociation. For instance, Bremner et al. (1992) demonstrated a link between war-induced PTSD and dissociation, and Winograd, Peluso, and Glover (1998) showed that dissociative symptoms were positively correlated with susceptibility to false memories on a DRM task. Thus a source-monitoring account would predict that PTSD patients should produce more false recall of critical lures on a DRM task. In fact, two studies have used the DRM paradigm with trauma-exposed people, a subset of whom had developed PTSD as a consequence, plus a group of individuals who had not experienced a severe trauma (Bremner et al., 2000 and Zoellner et al., 2000). Both studies used Roediger and McDermott’s (1995) materials, and tested memory for the words by recognition and free recall. In a recognition test, Zoellner et al. found that the PTSD group did not significantly differ from the non-PTSD group on either correctly recognizing presented words or on falsely recognizing critical lures. Bremner et al. also reported no difference between the groups for correct recognition but found that the PTSD group falsely recognised more critical lures than other trauma-exposed participants. When comparing the two trauma-exposed groups on correct recall of words, Zoellner et al. reported no difference, whereas Bremner et al. found that PTSD patients recalled fewer words than participants without PTSD. On numbers of critical lures mistakenly recalled, neither study reported significant differences between the two groups, and in both cases the trend was actually for non-PTSD participants to recall more lures. The present experiment was aimed at investigating this discrepancy between the results on correct recall of words from DRM lists. Furthermore, to shed more light on the unexpected finding in both previous studies of this issue that trauma-exposed groups have equivalent susceptibility to recall critical lures. In addition, a novelty of the present study was that trauma-related DRM lists were used, in addition to lists similar to Roediger and McDermott’s (see Geraerts, Smeets, Jelicic, van Heerden, & Merckelbach (2005), for a similar and independent development of trauma-related DRM). To the extent that studies show that PTSD patients and trauma-exposed non-PTSD patients show similar patterns on trauma-related cognitive tasks, this may pose a problem for models of cognition in PTSD, especially those predicting that trauma-exposed people who had developed PTSD would have impaired trauma-related cognition. For instance in Ehlers and Clark’s (2000) model, several sets of factors intervene between trauma exposure and the development of persistent PTSD: Besides the characteristics of the trauma and its sequelae, a person’s beliefs and coping style will play a role, as well as peritraumatic processing, and of most relevance here, an individual’s cognitive strategies aimed at inhibiting the reminders of the unpleasant event. In this model, PTSD patients have self-reinforcing thought patterns, where their attempts at pushing thoughts of the trauma out of their mind actually have the opposite effect of making the unpleasant thoughts rebound into consciousness more often. Trauma-related cognition would thus be expected to be particularly impaired for PTSD patients compared to trauma-exposed controls. In their study, Bremner et al. reported that PTSD symptoms correlated negatively with the number of correctly recalled words, but not with recall of critical lures. Zoellner et al., on the other hand, found that PTSD severity did not correlate significantly with the number of correctly recalled words but correlated positively with recall of critical lures. Furthermore, depressive symptoms did not correlate with either dependent variable. It was of interest to investigate the relations between the equivalent variables in our study. All of the traumas in Bremner et al.’s study and the majority in Zoellner et al.’s were sexual in nature. In the present study, the traumas were war-related: all of them had been exposed to war-related traumas, like bombs, shelling, injuries, and fires. There are as yet not enough data from the study of cognitive processes in PTSD to know whether to expect that different traumas would have different cognitive effects, but we note that models of information processing in PTSD, and the DSM classification appear to assume that different traumas will give rise to the same symptoms and underlying cognitive causes. In this study, we tested 50 participants with PTSD induced by war-related trauma, and 50 traumatised control participants without PTSD. The study investigated whether source-monitoring in general, and trauma-related source-monitoring in particular, are worse in PTSD, leading to more false recall of war-related critical lures. Also, if source-monitoring is impaired for trauma-related words in the PTSD group, then these false memories might be associated with more Remember responses. The study was carried out in 2003 in Tuzla, northern Bosnia, which was the main Muslim enclave during the war from 1992 to 1996. Therefore, the inducing events for the PTSD patients occurred at least 7 years previously. Mooren, de Jong, Kleber, and Ruvic (2003) reported that amongst their Bosnian control sample of 102 people not seeking clinical help in 1996, the mean score on the Impact of Event Scale was over 36. This is consistent with the notion that, because the war was one of the most brutal in living memory, there is a sense in which all Bosnians have been traumatised by it, and because all participants in the current study were Bosnian, and all but five of them spent the whole of the war in Bosnia, this will have tended to work against the hypotheses.