Source memory errors associated with reports of posttraumatic flashbacks: a proof of concept study

Flashbacks are involuntary, emotion-laden images experienced by individuals with posttraumatic stress disorder (PTSD). The qualities of flashbacks could under certain circumstances lead to source memory errors. Participants with PTSD wrote a trauma narrative and reported the experience of flashbacks. They were later presented with stimuli from flashback and non-flashback parts of their narrative, mixed with foils from the narrative of another participant, and judged whether they belonged to their own narrative. They also reported whether stimuli elicited a flashback during this recognition test. Overall reporting a flashback at test was associated with significantly better recognition performance. Flashbacks were occasionally reported to foil stimuli, which were then likely to be wrongly attributed to the person's own narrative. This provides proof of concept of a cognitive mechanism that could potentially account for some cases of false trauma memories.     

Specificity of episodic and semantic aspects of autobiographical memory in relation to symptoms of posttraumatic stress disorder (PTSD)

Two studies examined the relationship between the ability to access specific autobiographical material in memory and presence/symptoms of posttraumatic stress. In Study 1, a sample of refugees with a diagnosis of posttraumatic stress disorder (PTSD) completed the Autobiographical Memory Test (AMT) in which they had to generate specific episodic autobiographical memories in response to emotion-related cue words. Results showed that reduced specificity of memories on the AMT was associated with an increased frequency of trauma-related flashbacks but with reduced use of effortful avoidance to deal with trauma-related intrusions in the day-to-day. Study 2 examined retrieval of semantic autobiographical information from previous lifetime periods in groups of cancer survivors with posttraumatic stress and healthy controls. The cancer survivors were able to generate fewer specific semantic details about the personal past compared to the controls. The more symptomatic survivors showed the greatest memory impairment. The data from both studies are discussed in terms of compromised access to specific autobiographical material in distressed trauma survivors reflecting a process of affect regulation.     

A comparison of flashbacks and ordinary autobiographical memories of trauma: cognitive resources and behavioural observations

We investigated predictions derived from the dual representation theory of posttraumatic stress disorder, which proposes that flashbacks and ordinary memories of traumas are supported by different types of representation. Sixty-two participants, meeting DSM-IV diagnostic criteria for posttraumatic stress disorder, completed a detailed written trauma narrative, and afterwards identified those sections in the narrative that had been written in flashback and ordinary memory periods. Performance on cognitive tasks confirmed predictions that flashback periods would be associated with a specific decrement in visuospatial processing. Contrary to prediction, periods of both flashback and ordinary memory were associated with decrements on a verbal processing task. Independent observer ratings also confirmed that flashback periods were associated with increases in a wide range of autonomic and motor behaviours.     

Traumatic memories of war veterans: not so special after all

Several authors have argued that traumatic experiences are processed and remembered in a qualitatively different way from neutral events. To investigate this issue, we interviewed 121 Croatian war veterans diagnosed with posttraumatic stress disorder (PTSD) about amnesia, intrusions (i.e., flashbacks and nightmares), and the sensory qualities of their most horrific war memories. Additionally, they completed a self-report scale measuring dissociative experiences. In contrast to what one would expect on the basis of theories emphasizing the special status of traumatic memories, amnesia, and high frequency intrusions were not particularly typical for our sample of traumatized individuals. Moreover, traumatic memories were not qualitatively different from neutral memories with respect to their stability and sensory qualities. The severity of PTSD symptoms was not significantly correlated with dissociative experiences. Our findings do not support the existence of special memory mechanisms that are unique to experiencing traumatic events.     

Neural correlates of music recognition in Down syndrome

The brain mechanisms that subserve music recognition remain unclear despite increasing interest in this process. Here we report the results of a magnetoencephalography experiment to determine the temporal dynamics and spatial distribution of brain regions activated during listening to a familiar and unfamiliar instrumental melody in control adults and adults with Down syndrome (DS). In the control group, listening to the familiar melody relative to the unfamiliar melody, revealed early and significant activations in the left primary auditory cortex, followed by activity in the limbic and sensory-motor regions and finally, activation in the motor related areas. In the DS group, listening to the familiar melody relative to the unfamiliar melody revealed increased significant activations in only three regions. Activity began in the left primary auditory cortex and the superior temporal gyrus and was followed by enhanced activity in the right precentral gyrus. These data suggest that familiar music is associated with auditory–motor coupling but does not activate brain areas involved in emotional processing in DS. These findings reveal new insights on the neural basis of music perception in DS as well as the temporal course of neural activity in control adults.     

Incidental retrieval of emotional contexts in post-traumatic stress disorder and depression: an fMRI study

In the present study, we used fMRI to assess patients suffering from post-traumatic stress disorder (PTSD) or depression, and trauma-exposed controls, during an episodic memory retrieval task that included non-trauma-related emotional information. In the study phase of the task neutral pictures were presented in emotional or neutral contexts. Participants were scanned during the test phase, when they were presented with old and new neutral images in a yes/no recognition memory task. fMRI results for the contrast between old and new items revealed activation in a predominantly left-sided network of cortical regions including the left middle temporal, bilateral posterior cingulate, and left prefrontal cortices. Activity common to all three groups when correctly judging pictures encoded in emotional contexts was much more limited. Relative to the control and depressed groups the PTSD group exhibited greater sensitivity to correctly recognised stimuli in the left amygdala/ventral striatum and right occipital cortex, and more specific sensitivity to items encoded in emotional contexts in the right precuneus, left superior frontal gyrus, and bilateral insula. These results are consistent with a substantially intact neural system supporting episodic retrieval in patients suffering from PTSD. Moreover, there was little indication that PTSD is associated with a marked change in the way negatively valenced information, not of personal significance, is processed.     

Veridical and false memory for scenic material in posttraumatic stress disorder

The question whether memory aberrations in posttraumatic stress disorder (PTSD) also manifest as an increased production of false memories is important for both theoretical and practical reasons, but is yet unsolved. Therefore, for the present study we investigated veridical and false recognition in PTSD with a new scenic variant of the Deese-Roediger-McDermott (DRM) paradigm, which was administered to traumatized individuals with PTSD (n=32), traumatized individuals without PTSD (n=30), and non-traumatized controls (n=30). The PTSD group neither produced higher rates of false memories nor expressed more confidence in errors, but did show inferior memory sensitivity. Whereas depressive symptoms did not correlate with veridical nor false recognition, state dissociation was positively associated with false memories.     

Neural correlates of successful and unsuccessful verbal memory encoding

Recent neuroimaging studies suggest that episodic memory encoding involves a network of neocortical structures which may act interdependently with medial temporal lobe (mTL) structures to promote the formation of durable memories, and that activation in certain structures is modulated according to task performance. Functional magnetic resonance imaging (fMRI) was used to determine the neural structures recruited during a verbal episodic encoding task and to examine the relationship between activation during encoding and subsequent recognition memory performance across subjects. Our results show performance-correlated activation during encoding both in neocortical and medial temporal structures. Neocortical activations associated with later successful and unsuccessful recognition memory were found to differ not only in magnitude, but also in hemispheric laterality. These performance-related hemispheric effects, which have not been previously reported, may correspond to between-subject differences in encoding strategy.     

Bi-hemispheric engagement in the retrieval of autobiographical episodes

Functional magnetic resonance imaging (fMRI) was used to study the neural correlates of neutral, stressful, negative and positive autobiographical memories. The brain activity produced by these different kinds of episodic memory did not differ significantly, but a common pattern of activation for different kinds of autobiographical memory was revealed that included (1) largely bilateral portions of the medial and superior temporal lobes, hippocampus and parahippocampus, (2) portions of the ventral, medial, superior and dorsolateral prefrontal cortex, (3) the anterior and posterior cingulate, including the retrosplenial, cortex, (4) the parietal cortex, and (5) portions of the cerebellum. The brain regions that were mainly activated constituted an interactive network of temporal and prefrontal areas associated with structures of the extended limbic system. The main bilateral activations with left-sided preponderance probably reflected reactivation of complex semantic and episodic self-related information representations that included previously experienced contexts. In conclusion, the earlier view of a strict left versus right prefrontal laterality in the retrieval of semantic as opposed to episodic autobiographical memory, may have to be modified by considering contextual variables such as task demands and subject variables. Consequently, autobiographical memory integration should be viewed as based on distributed bi-hemispheric neural networks supporting multi-modal, emotionally coloured components of personal episodes.     

Common pathways in mental imagery and pain perception: an fMRI study of a subject with an amputated arm

The present paper reviews data from two previous studies in our laboratory, as well as some additional new data, on the neuronal representation of movement and pain imagery in a subject with an amputated right arm. The subject imagined painful and non-painful finger movements in the amputated stump while being in a MRI scanner, acquiring EPI-images for fMRI analysis. In Study I (Ersland et al., 1996) the Subject alternated tapping with his intact left hand fingers and imagining "tapping" with the fingers of his amputated right arm. The results showed increased neuronal activation in the right motor cortex (precentral gyrus) when tapping with the fingers of the left hand, and a corresponding activation in the left motor cortex when imagining tapping with the fingers of the amputated right arm. Finger tappings of the intact left hand fingers also resulted in a larger activated precentral area than imagery "finger tapping" of the amputated right arm fingers. In Study II (Rosen et al., 2001 in press) the same subject imagining painful and pleasurable finger movements, and still positions of the fingers of the amputated arm. The results showed larger activations over the motor cortex for movement imagining versus imagining the hand being in a still position, and larger activations over the sensory cortex when imagining painful experiences. It can therefore be concluded that not only does imagery activate the same motor areas as real finger movements, but also that adding instructions of pain together with imaging moving the fingers intensified the activation compared with adding instructions about non-painful experiences. From these studies, it is clear that areas activated during actual motor execution to a large extent also are activated during mental imagery of the same motor commands. In this respect the present studies add to studies of visual imagery that have shown a similar correspondence in activation between actual object perception and imagery of the same object.     

Overgeneral autobiographical memory recollection in Iranian combat veterans with posttraumatic stress disorder

This study examined the recollection of autobiographical material in memory among Iranian military veterans with and without posttraumatic stress disorder (PTSD), and healthy non-trauma-exposed control subjects. Participants completed the Autobiographical Memory Test, Autobiographical Memory Interview (counterbalanced), Impact of Event Scale-Revised, Beck Depression Inventory-II, Wechsler Memory Scale-III and Wechsler Adult Intelligence Scale-Revised. The PTSD group generated fewer specific episodic and semantic details of autobiographical memory compared to the non-PTSD and control groups. Working memory did not significantly moderate the relationship between PTSD diagnosis and reduced autobiographical memory specificity but did moderate the relationship between PTSD diagnosis and semantic recall; semantic memory recall was not significantly related to working memory ability for those with PTSD but was related to working memory ability for trauma survivors without PTSD. While the data provide some support for the expectation that higher working memory ability is associated with an increased ability to retrieve specific memories (i.e. semantic memory recall in those without PTSD), the findings are also consistent with the view that for those with PTSD the demands on working memory required for affect regulation cancel out this influence of working memory in augmenting access to specific memories.     

Amnesia,flashbacks, nightmares,and dissociation in aging concentration camp survivors

The current study examined to what extent war memories of Dutch survivors of Japanese/Indonesian concentration camps display characteristics that are often believed to be typical for traumatic memories. Twenty-nine survivors were interviewed about amnesia, flashbacks, nightmares and the sensory quality of their most upsetting war memories. In addition, they completed self-report scales measuring post-traumatic stress symptoms and dissociation. In contrast to prevailing notions, amnesia, flashbacks and nightmares were not typical for this sample. Neither were traumatic memories characterized by a particularly strong sensory loading. Post-traumatic stress symptoms were not related to dissociative experiences. At least for this group of aging survivors, it appears that the pathogenic potential of traumatic memories has more to do with their extremely aversive content than with a qualitatively different type of organization of these memories.     

人类记忆再巩固研究现状及临床应用

巩固的记忆被提取后,进入不稳定状态,再重新稳定下来,这个过程称为记忆再巩固。本文首先阐述人类记忆再巩固主要研究方法和经典范式,梳理记忆再巩固在人类恐惧记忆和情景记忆两个方面的相关研究,并从认知神经科学角度整理记忆再巩固的加工机制。然后总结记忆再巩固应用于创伤性应激障碍和药物成瘾等心理障碍临床治疗的相关文献。最后本文提出未来研究的方向和建议,希冀对人类记忆再巩固的理论研究和临床应用提供新思路。     

Episodic retrieval and the cortical binding of relational activity

Retrieval of episodic memories depends on the successful “re-collection” of event features, such as the time, place, people, thoughts, and feelings associated with a past experience.In neuroimaging studies, ventral regions of the posterior parietal cortex (vPPC) are particularly active when episodic memories are successfully retrieved. A review of the neural correlates of episodic retrieval is presented along with a new theory, cortical binding of relational activity (CoBRA). According to CoBRA, the vPPC acts as a convergence zone that binds episodic features stored in disparate neocortical regions. This process works in conjunction with other known mechanisms, such as those associated with the prefrontal cortex and medial temporal lobe.     

A comparison of flashbacks and ordinary autobiographical memories of trauma: content and language

We investigated hypotheses derived from the dual representation theory of posttraumatic stress disorder, which proposes that flashbacks and ordinary memories of trauma are supported by different types of representation. Sixty-two participants meeting diagnostic criteria for posttraumatic stress disorder completed a detailed written trauma narrative, and afterwards identified those sections in the narrative that had been written in flashback and ordinary memory periods. As predicted, flashback periods were characterised by greater use of detail, particularly perceptual detail, by more mentions of death, more use of the present tense, and more mention of fear, helplessness, and horror. In contrast, ordinary memory sections were characterised by more mention of secondary emotions such as guilt and anger.     

rTMS for PTSD: induced merciful oblivion or elimination of abnormal hypermnesia?

Neuroimaging studies and experimental data suggest that symptoms of posttraumatic stress disorder (PTSD) are associated with dysfunctions of neural circuits linking prefrontal cortex and the limbic system that have a role in autobiographic episodic memory. High-frequency repetitive transcranial magnetic stimulation (rTMS) of the right dorsolateral prefrontal cortex (DLPFC) has been suggested to be beneficial to patients with PTSD, transiently alleviating re-experiencing as well as avoidance reactions and associated anxiety symptoms. In healthy humans, converging evidence suggests that rTMS of the right DLPFC interferes with episodic memory retrieval. Hence, we hypothesize that daily applications of rTMS in PTSD patients may reduce access to the set of autobiographical stored events, that, if re-experienced, may cause the overt PTSD symptoms.     

Brain activations associated with shifts in response criterion on a recognition test.

Sensitivity and bias can be manipulated independently on a recognition test. The goal of this fMRI study was to determine whether neural activations associated with manipulations of a decision criterion would be anatomically distinct from neural activations associated with manipulations of memory strength and episodic retrieval. The results indicated that activations associated with shifting criteria (a manipulation of bias) were located in bilateral regions of the lateral cerebellum, lateral parietal lobe, and the dorsolateral prefrontal cortex extending from the supplementary motor area. These regions were anatomically distinct from activations in the prefrontal cortex produced during memory-based retrieval processes (manipulations of sensitivity), which tended to be more medial and anterior. These later activations are consistent with previous studies of episodic retrieval. Determining patterns of neural activations associated with decision-making processes relative to memory processes has important implications for Cognitive Neuroscience, including the use of these patterns to compare memory models in different paradigms.     

The neural regions sustaining episodic encoding and recognition of objects

In this functional MRI experiment, encoding of objects was associated with activation in left ventrolateral prefrontal/insular and right dorsolateral prefrontal and fusiform regions as well as in the left putamen. By contrast, correct recognition of previously learned objects (R judgments) produced activation in left superior frontal, bilateral inferior frontal, and right cerebellar regions, whereas correct rejection of distractor objects (N judgments) was associated with activation in bilateral prefrontal and anterior cingulate cortices, in right parietal and cerebellar regions, in the left putamen, and in the right caudate nucleus. The R minus N comparison showed activation in the left lateral prefrontal cortex and in bilateral cingulate cortices and precunei, while the N minus R comparison did not reveal any positive signal change. These results support the view that similar regions of the frontal lobe are involved in episodic encoding and retrieval processes, and that the successful episodic retrieval of newly learned objects is mainly based on a frontoparietal network.     

The role of the left hemisphere in motor control of touch: a functional magnetic resonance imaging analysis

Previous research using a simple finger-touching task has shown greater blood oxygenation level dependent (BOLD) activation volume in the motor cortex of the right hemisphere for contralateral finger touching compared to ipsilateral finger touching, but no significant contralateral advantage for the left hemisphere. Such equal involvement of the left hemisphere for both contralateral and ipsilateral finger touching suggests a special role of the left hemisphere for finger touching. In contrast, we found a contralateral advantage in the motor cortex of both hemispheres in a majority of participants (14/16) when consistently activated BOLD volumes were examined. However, participants who did not show a clear contralateral advantage for the left hemisphere did show activation in the left inferior frontal gyrus (IFG; Broca's Area) and in the left insular cortex, which suggests that verbally mediated sequencing of finger movements can account for our less frequent result.