Can Cognitive Neuroscience Illuminate the Nature of Traumatic Childhood Memories? Daniel L Schacterl, Wilma Koutstaal and Kenneth a Norman
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207 Can cognitive neuroscience illuminate the nature of traumatic childhood memories? Daniel L Schacterl, Wilma Koutstaal and Kenneth A Norman Recent findings from cognitive neuroscience and cognitive distortion? Can traumatic events be forgotten, and if so, psychology may help explain why recovered memories of can they be later recovered? We first consider evidence trauma are sometimes illusory. In particular, the notion of that pertains to claims of recovered memories of trauma. defective source monitoring has been used to explain a wide We then consider the relevant memory phenomena in the range of recently established memory distortions and illusions. context of concepts and findings from the contemporary Conversely, the results of a number of studies may potentially cognitive neuroscience of memory. be relevant to forgetting and recovery of accurate memories, including studies demonstrating reduced hippocampal volume The recovered memories debate: what do we in survivors of sexual abuse, and recovery from functional and know? organic retrograde amnesia. Other recent findings of interest The controversy over recovered memories is a complex include the possibility that state-dependent memory could be affair that involves several intertwined psychological and induced by stress-related hormones, new pharmacological social issues (for elaboration of this point, see [8-131). models of dissociative states, and evidence for ‘repression’ in Here, we consider four critical questions. First, can patients with right parietal brain damage. memories of abuse be forgotten? Second, does the evidence warrant the postulation of a special mechanism Address of repression? Third, can memories of childhood trauma, Department of Psychology, William James Hall, Harvard University, if forgotten, later be remembered accurately? And, finally, 33 Kirkland Street, Cambridge, Massachusetts 02138, USA is there evidence that false memories of abuse can occur? ‘e-mail: [email protected] Abbreviation Can memories of abuse be forgotten? NMDA N-methyl-o-aspartate In several studies, patients who reported that they were sexually abused as children also said there were periods of time in the past when they had forgotten about Current Opinion in Neurobiology 1996, 6:207-214 the abuse [14-171. However, these studies provide only 0 Current Biology Ltd ISSN 0959-4388 weak evidence that abuse can be forgotten, because, first, none of them contained corroborating evidence that the reported abuse had actually occurred, and second, all Introduction of them relied on retrospective estimates of forgetting, Cognitive neuroscience studies of memory have many which are of questionable validity (for a discussion, see important implications for everyday life. Such implications [5,&l&19]). Stronger evidence for forgetting has been are nowhere more evident than in the recent explosion provided by Williams [ZO**], who found that 38% of of cases in which adult women and men, usually in women who had been brought to a hospital emergency the context of psychotherapy, claim to have recovered room as children for treatment of abuse failed to report long-forgotten memories of childhood abuse suffered the incident when interviewed two decades later. Most at the hands of parents, friends, or other adults. The remembered other episodes of abuse, but 12% reported no memories range from single incidents of inappropriate memory of any abuse. Likewise, several individual cases fondling to years of rape and even ritualistic abuse. have been reported in which incidents of corroborated People who recover such memories are often certain abuse were temporarily forgotten (e.g. [13,21]). Thus, that they reflect actual past events. This conviction is although the evidence indicates that most adults who were shared by some psychotherapists, who have argued that abused during childhood always remember their abuse, it memories of sexual abuse can be repressed and later also shows that some abusive episodes can be forgotten. recovered (e.g. [l-3]). Yet, those who are accused of perpetrating the abuse frequently deny that the incidents Does the evidence warrant postulation of a special ever occurred. A variety of psychologists, psychiatrists, and mechanism of repression? others have argued that recovered memories are frequently Although it is apparent that forgetting of abusive events illusory and are attributable to suggestive practices used in can occur, ordinary mechanisms of forgetting, such as psychotherapy (cf. [4’,5-81). decay, interference, or infantile and childhood amnesia, are probably sufficient to explain inaccessibility of some The recovered memories debate raises issues that are traumatic incidents [22,23]. For example, when people fail relevant to cognitive neuroscience. How accurate is to remember single incidents of sexual abuse that occurred memory and under what conditions is it subject to when they were children (e.g. [20*“,.21]), forgetting may 208 Cognitive neuroscience be caused by the same ordinary mechanisms that are has ever been uncovered despite extensive investigations responsible for forgetting of non-traumatic experiences. by law enforcement agencies [7,34,35]. Finally, a growing number of people have disavowed or ‘retracted’ their In contrast, when people claim to have forgotten about ex- recovered memories, and recent evidence indicates that tended periods of repeated and horrific abuse, something many of these individuals were treated by therapists who more than ordinary forgetting is probably involved. Ai- used suggestive techniques to recover memories [36]. though there is little firm evidence for such extraordinary forgetting, some researchers have invoked the concept of Our brief overview of recovered memories reveals, there- repression to account for it (e.g. [1,3]). The notion of fore, that some may be accurate and others illusory. repression has a long and controversial history, dating to We now examine insights and evidence from cognitive Freud’s early contributions (see [24]), and the strength of neuroscience that are relevant to both sides of the issue. the evidence for it depends on how the concept is defined. Illusory memories: cognitive and On the one hand, repression may be defined as a neurobiological perspectives process of conscious avoidance, in which a person fails Memory usually preserves a reasonably accurate rep- to think about, talk about, or otherwise rehearse an resentation of the past. Nonetheless, most researchers unpleasant experience. Cognitive research has shown that acknowledge that memory does not preserve an exact such motivated or ‘directed’ forgetting can lead to a or ‘photographic’ representation of all aspects of past reduced likelihood of recalling an event (see [25] for a experiences. Instead, memory is a fundamentally con- review). On the other hand, repression may be defined as structive process. Cognitive psychologists have argued an automatic, defensive process that functions to exclude that memories of past experiences are constructed from threatening material from awareness. However, little or no several sources: stored fragments of an event; pre-existing experimental evidence for this latter kind of repression knowledge, beliefs, and expectations that the rememberer exists [l&26]. With respect to the recovered memories brings to an experience; and properties of the environment debate, the consciously motivated form of repression that in which the experience is retrieved (cf. [12,37-42]). results in failure to rehearse or think about traumatic Likewise, neuroscientists have argued that memories are events could account for gradual forgetting of an abusive constructed on the basis of stored fragments of experiences episode or episodes over time (see, for example, [27]). that are distributed throughout a variety of cortical However, this form of repression does not seem powerful regions and are bound together by systems that work enough to produce severe amnesia for repeated, horrific co-operatively with cortical storage areas during encoding events soon after they occur. and retrieval (cf. [43-46]). From both the cognitive and neurobiological perspectives, memory distortions are Can memories of childhood trauma, if forgotten, later be a natural by-product of the fundamentally constructive remembered accurately? nature of the memory process [12]. The fact that some episodes of abuse can be forgotten need not mean that they can be recalled again years Recent research has begun to illuminate the cogni- later. However, several cases have been reported in which tive and neurobiological factors that contribute to illu- people who have recovered previously forgotten memories sory memories. One important phenomenon is known of abuse have obtained corroboration that the abuse as source memory or source monitoring-remembering occurred (e.g. [ 13,21,27]; for discussion of corroborated when, where and how a memory was acquired [39]. cases, see [8,12]). Recovery of such memories may simply Numerous studies with college students have shown that reflect the well established fact that appropriate retrieval recollections of external events and internal imaginings cues can produce recall of aspects of seemingly forgotten can be confused, thereby producing distorted memories experiences (e.g. [28,29]). (e.g. [47]). Failures of source memory also play a key role in memory distortions that occur when people are Is there evidence thet false memories of abuse can occur? exposed to misleading post-event suggestions, as observed There is