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.     

Protein synthesis underlies post-retrieval memory consolidation to a restricted degree only when updated information is obtained

Consolidation theory proposes that through the synthesis of new proteins recently acquired memories are strengthened over time into a stable long-term memory trace. However, evidence has accumulated suggesting that retrieved memory is susceptible to disruption, seeming to consolidate again (reconsolidate) to be retained in long-term storage. Here we show that intracortical blockade of protein synthesis in the gustatory cortex after retrieval of taste-recognition memory disrupts previously consolidated memory to a restricted degree only if the experience is updated. Our results suggest that retrieved memory can be modified as part of a mechanism for incorporating updated information into previously consolidated memory.     

Modulation of retrieval processing reflects accuracy of emotional source memory

There is considerable evidence that encoding and consolidation of memory are modulated by emotion, but the retrieval of emotional memories is not well characterized. Here we manipulated the emotional context with which affectively neutral stimuli were associated during encoding, allowing us to examine neural activity associated with retrieval of emotional memories without confounding the emotional attributes of cue items and the retrieved context. Using a source memory procedure we were also able to compare how retrieval processing was modulated when the emotional encoding context was recollected or not. An interaction between emotional encoding context and accuracy of source memory revealed that successful retrieval of emotional context was associated with activity in left amygdala, and a left frontotemporal network including anterior insula, prefrontal cortex and cingulate. In contrast, when contextual retrieval was unsuccessful, items encoded in emotional contexts elicited enhanced activity in right amygdala and a right-lateralized network that included extrastriate visual areas. These findings indicate distinct effects of emotion on successful and unsuccessful retrieval of source information, including lateralization of amygdala responses.     

Personality traits and the retrieval of positive and negative memories

The relationship between personality traits, current mood state and the retrieval of positive and negative memories was investigated. Fifty-nine subjects retrieved a series of memories in response to a list of 20 stimulus words and subsequently rated those memories on pleasant/unpleasant and happy/unhappy scales. After controlling for the effect of mood states, Extraversion related primarily to the retrieval of more positive memories, Neuroticism to both fewer positive and more negative memories and Psychoticism mainly to fewer positive memories. The relevance of these findings to studies demonstrating a relation between mood and memory retrieval is discussed.     

抑制引起的遗忘及其神经机制

当面对不愉快的提醒时, 人们通常会试图阻止那些不想要的记忆出现在脑海中。先前的研究表明, 抑制不想要的记忆的检索会降低这些记忆的可及性, 引起遗忘, 这一效应称为抑制引起的遗忘(suppression- induced forgetting, SIF)。SIF的神经机制涉及右背外侧前额叶皮层和额中回的激活增加, 以及海马的激活受到抑制。SIF的程度受记忆材料的情绪效价、个体的病理性情绪状态和训练的影响。未来研究应在深入了解SIF神经机制的基础上, 考虑如何提高临床病理性记忆的SIF效果, 以达到治疗目的。     

Does retrieval intentionality really matter? Similarities and differences between involuntary memories and directly and generatively retrieved voluntary memories

Theories of autobiographical memory distinguish between involuntary and voluntary retrieval as a consequence of conscious intention (i.e., wanting to remember). Another distinction can be made between direct and generative retrieval, which reflects the effort involved (i.e., trying to remember). However, it is unclear how intention and effort interacts. For example, involuntary memories and directly retrieved memories have been used interchangeably in the literature to refer to the same phenomenon of effortless, non‐strategic retrieval. More recent theoretical advances suggest that they are separate types of retrieval, one unintentional (involuntary), another intentional and effortless (direct voluntary retrieval), and a third intentional and effortful (generative voluntary retrieval). Whether this also entails differing phenomenological characteristics, such as vividness, rehearsal, or emotional valence, has not been previously investigated. In the current study, participants reported memories in an experimental paradigm designed to elicit voluntary and involuntary memories and rated them on a number of characteristics. If intention affects the retrieval process, then we should expect differences between the characteristics of involuntary and directly retrieved memories. The results imply that retrieval intention seems to differentiate how a memory appears in a person's mind. Furthermore, we argue that these differences in part could result from differences in encoding and consolidation.     

Mood-dependent retrieval in visual long-term memory: dissociable effects on retrieval probability and mnemonic precision

Although memories are more retrievable if observers’ emotional states are consistent between encoding and retrieval, it is unclear whether the consistency of emotional states increases the likelihood of successful memory retrieval, the precision of retrieved memories, or both. The present study tested visual long-term memory for everyday objects while consistent or inconsistent emotional contexts between encoding and retrieval were induced using background grey-scale images from the International Affective Picture System (IAPS). In the study phase, participants remembered colours of sequentially presented objects in a negative (Experiment 1a) or positive (Experiment 2a) context. In the test phase, participants estimated the colours of previously studied objects in either negative versus neutral (Experiment 1a) or positive versus neutral (Experiment 2a) contexts. Note, IAPS images in the test phase were always visually different from those initially paired with the studied objects. We found that reinstating negative context and positive context at retrieval resulted in better mnemonic precision and a higher probability of successful retrieval, respectively. Critically, these effects could not be attributed to a negative or positive context at retrieval alone (Experiments 1b and 2b). Together, these findings demonstrated dissociable effects of emotion on the quantitative and qualitative aspects of visual long-term memory retrieval.     

The role of the amygdala in emotional experience during retrieval of personal memories

ABSTRACT

Although the role of the amygdala in emotional memory retrieval has long been established, how such engagement varies depending on valence and retrieval context is less clearly understood. Participants retrieved personal memories associated with primarily positive, primarily negative, and mixed-valence images, pressing a button when successful. The button press divided trials into search and elaboration phases. Participants provided positivity and negativity ratings immediately following each trial, and then again in a post-retrieval survey. The relation between amygdala recruitment and emotionality exhibited a four-way interaction, with no other significant main effects or interactions. The interaction was driven by a temporal shift in the role of amygdala recruitment during retrieval of memories associated with mixed-valence images: Negativity ratings were supported more by search-related activity whereas positivity was more strongly associated with elaboration. Amygdala activity during retrieval relates to emotional experience in more complicated ways than previously understood. When participants were able to consider positive and negative aspects of the same event, amygdala recruitment during search and elaboration were associated with opposite behavioural effects. Such findings suggest that the amygdala may support distinct aspects of emotional experience for the same memory depending on when during retrieval it is recruited.     

Understanding cognitive behaviour therapy: A retrieval competition account

Vulnerability to emotional disorders is thought to lie in memory representations (e.g. negative self-schemas) that are activated by triggering events and maintain negative mood. There has been considerable uncertainty about how the influence of these representations can be altered, prompted in part by the development of new metacognitive therapies. This article reviews research suggesting there are multiple memories involving the self that compete to be retrieved. It is proposed that CBT does not directly modify negative information in memory, but produces changes in the relative activation of positive and negative representations such that the positive ones are assisted to win the retrieval competition. This account is related to the treatment of common symptoms typical of emotional disorders, such as phobic reactions, rumination, and intrusive images and memories. It is shown to provide a parsimonious set of principles that have the potential to unify traditional and more modern variants of CBT.     

Gamma oscillations distinguish true from false memories

ABSTRACT— To test whether distinct patterns of electrophysiological activity prior to a response can distinguish true from false memories, we analyzed intracranial electroencephalographic recordings while 52 patients undergoing treatment for epilepsy performed a verbal free-recall task. These analyses revealed that the same pattern of gamma-band (28–100 Hz) oscillatory activity that predicts successful memory formation at item encoding—increased gamma power in the hippocampus, prefrontal cortex, and left temporal lobe—reemerges at retrieval to distinguish correct from incorrect responses. The timing of these oscillatory effects suggests that self-cued memory retrieval begins in the hippocampus and then spreads to the cortex. Thus, retrieval of true, as compared with false, memories induces a distinct pattern of gamma oscillations, possibly reflecting recollection of contextual information associated with past experience.     

Retrieval effort or intention: Which is more important for participants’ classification of involuntary and voluntary memories?

Theories of autobiographical memory distinguish between involuntary and voluntary memories. While involuntary memories are retrieved with no conscious intention and are therefore unexpected, voluntary memories are both intended and expected. Recent research has shown that participants sometimes classify their memories as either involuntary or voluntary based on retrieval effort instead of intention. These findings question whether intention really is the defining difference between these two types of retrieval or whether retrieval effort is also an important determinant. In two experimental studies, we investigated the extent to which participants rely on retrieval effort while classifying their memories as involuntary or voluntary. We created experimental conditions that maximize the probability of one type of retrieval while minimizing the probability of another type. Participants reported autobiographical memories in each condition while the programme registered their retrieval time. They then classified their memories as either voluntary or involuntary and rated all memories on perceived retrieval effort. This gave us four categories of memories: experimentally defined voluntary and involuntary memories with an objective measure of effort (retrieval time) and subjectively classified involuntary and voluntary memories with a subjective measure of effort. This allowed us to investigate the relative contribution of intention and effort to involuntary and voluntary memories. We replicated and extended previous findings by showing that the majority of memories were classified as involuntary independently of whether they were retrieved in the experimentally defined voluntary or involuntary condition. This could indicate that subjective effort is more important than intention for the involuntary–voluntary distinction in contrast with existing theories. We discuss theoretical and methodological implications of this finding.     

对人类不良记忆的修饰：来自记忆再巩固的证据

已经巩固的长时记忆被再次提取后, 进入一个记忆的不稳定期, 在此过程中, 记忆可被更新、强化、削弱甚至抹除, 这个过程称为再巩固。人类不良记忆再巩固研究揭示记忆激活后口服普萘洛尔(propranolol)或进行消退训练可削弱或抹除不良情绪记忆, 此过程中涉及杏仁核、海马、前额叶皮层等脑区的参与及其构成的神经环路的调控。当前临床上利用再巩固原理可通过药物治疗、行为干预或无创脑部刺激的方法改变不良记忆。然而, 由于其形成过程复杂并受多种因素影响, 未来研究应尽可能模拟临床中人类不良记忆形成的复杂环境, 深入探讨再巩固“边界问题”, 推动实验室研究向临床应用的转化。     

Contributions of the medial temporal lobe to declarative memory retrieval: manipulating the amount of contextual retrieval

We investigated how the hippocampus and its adjacent mediotemporal structures contribute to contextual and noncontextual declarative memory retrieval by manipulating the amount of contextual information across two levels of the same contextual dimension in a source memory task. A first analysis identified medial temporal lobe (MTL) substructures mediating either contextual or noncontextual retrieval. A linearly weighted analysis elucidated which MTL substructures show a gradually increasing neural activity, depending on the amount of contextual information retrieved. A hippocampal engagement was found during both levels of source memory but not during item memory retrieval. The anterior MTL including the perirhinal cortex was only engaged during item memory retrieval by an activity decrease. Only the posterior parahippocampal cortex showed an activation increasing with the amount of contextual information retrieved. If one assumes a roughly linear relationship between the blood-oxygenation level-dependent (BOLD) signal and the associated cognitive process, our results suggest that the posterior parahippocampal cortex is involved in contextual retrieval on the basis of memory strength while the hippocampus processes representations of item-context binding. The anterior MTL including perirhinal cortex seems to be particularly engaged in familiarity-based item recognition. If one assumes departure from linearity, however, our results can also be explained by one-dimensional modulation of memory strength.     

Testing the exclusivity effect in location memory

There is growing literature exploring the possibility of parallel retrieval of location memories, although this literature focuses primarily on the speed of retrieval with little attention to the accuracy of location memory recall. Baguley, Lansdale, Lines, and Parkin (2006) found that when a person has two or more memories for an object's location, their recall accuracy suggests that only one representation can be retrieved at a time (exclusivity). This finding is counterintuitive given evidence of non-exclusive recall in the wider memory literature. The current experiment explored the exclusivity effect further and aimed to promote an alternative outcome (i.e., independence or superadditivity) by encouraging the participants to combine multiple representations of space at encoding or retrieval. This was encouraged by using anchor (points of reference) labels that could be combined to form a single strongly associated combination. It was hypothesised that the ability to combine the anchor labels would allow the two representations to be retrieved concurrently, generating higher levels of recall accuracy. The results demonstrate further support for the exclusivity hypothesis, showing no significant improvement in recall accuracy when there are multiple representations of a target object's location as compared to a single representation.     

Effects of induced elation-depression on the accessibility of memories of happy and unhappy experiences

Elated and depressed moods were induced in student volunteers on separate occasions. On each occasion they retrieved past real-life experiences associated to stimulus words presented. Subjects subsequently rated the experiences for happiness-unhappiness and pleasantness-unpleasantness on a third occasion in a neutral mood state. Extremely unhappy memories were significantly more likely to be retrieved in the depressed mood than in the elated mood. Extremely happy memories were significantly more likely to be retrieved in the elated mood than in the depressed mood. Measures of latency of retrieval showed a significant interaction between mood state and type of memory. The results confirm the generality of previous findings in suggesting an effect of mood state on the accessibility of different types of cognition. The results are considered in relation to mood as a context in contextual-specific encoding and retrieval, and in relation to models and treatment of clinical conditions.     

Source accuracy data reveal the thresholded nature of human episodic memory

Episodic recollection supports conscious retrieval of past events. It is unknown why recollected memories are often vivid, but at other times we struggle to remember. Such experiences might reflect a recollection threshold: Either the threshold is exceeded and information is retrieved, or recollection fails completely. Alternatively, retrieval failure could reflect weak memory: Recollection could behave as a continuous signal, always yielding some variable degree of information. Here we reconcile these views, using a novel source memory task that measures retrieval accuracy directly. We show that recollection is thresholded, such that retrieval sometimes simply fails. Our technique clarifies a fundamental property of memory and allows responses to be accurately measured, without recourse to subjective introspection. These findings raise new questions about how successful retrieval is determined and why it declines with age and disease.     

Looking at remembering: Eye movements,pupil size,and autobiographical memory

To examine the relationship between visual imagery and autobiographical memory, eye position and pupil size were recorded while participants first searched for memories and then reconstructed the retrieved memories (Experiment 1), or only searched for memories (Experiment 2). In Experiment 1, we observed that, although recollective experience was not associated with the number of fixations per minute, memories that took longer to retrieve were linked to increased pupil size. In Experiment 2, we observed that directly retrieved memories were recalled more quickly and were accompanied by smaller pupils than generatively retrieved memories. After correcting for response time, retrieval mode also produced an effect, showing that decreased pupil size is not simply due to directly retrieved memories being recalled more quickly. These findings provide compelling evidence that objective measures, such as pupil size, can be used alongside subjective measures, such as self-reports, to distinguish between directly retrieved and generatively retrieved memories.     

How intention to retrieve a memory and expectation that a memory will come to mind influence the retrieval of autobiographical memories

While involuntary memories are retrieved with no intention and are usually unexpected (when one is not waiting for a memory to arise), voluntary memories are intended and expected (when one is searching and waiting for a memory to arise). The present study aimed to investigate the effects of retrieval intentionality (i.e. wanting to retrieve a memory) and monitoring processes (i.e. waiting for a memory to appear) during autobiographical memory retrieval. In addition, we introduced two novel laboratory conditions that have not been used in previous research on voluntary memories: in the first, participants were asked to report anything they could think of in response to each cue word; in the second, they could skip a word if nothing came to mind. These novel manipulations allowed us to differentiate between voluntary memories retrieved in response to experimenter-generated cues (when participants were forced to provide a memory or a thought for each cue) and self-selected cues (when participants were free to not answer a cue if they found it too difficult). We found that highly accessible memories were mostly experienced when retrieval was involuntary and unexpected, while memories with low accessibility were accessed through intentional retrieval and monitoring processes. Response times for memories recalled in the experimenter-generated cue conditions were longer compared to the self-selected cue conditions. This novel finding shows that experimenter-generated recall favours memories with low accessibility; it further supports the idea that, in a substantial number of trials, voluntary memories are directly rather than effortfully retrieved. The idea that the driving force behind differences between involuntary and voluntary memories is not the intention per se is further discussed.     

Neural correlates underlying true and false associative memories

Despite the fact that associative memory studies produce a large number of false memories, neuroimaging analyses utilizing this paradigm typically focus only on neural activity mediating successful retrieval. The current study sought to expand on this prior research by examining the neural basis of both true and false associative memories. Though associative false memories are substantially different than those found in semantic or perceptual false memory paradigms, results suggest that associative false memories are mediated by similar neural mechanisms. Specifically, we found increased frontal activity that likely represents enhanced monitoring and evaluation compared to that needed for true memories and correct rejections. Results also indicated that true, and not false associative memories, are mediated by neural activity in the MTL, specifically the hippocampus. Finally, while activity in early visual cortex distinguished true from false memories, a lack of neural differences between hits and correct rejections failed to support previous findings suggesting that activity in early visual cortex represents sensory reactivation of encoding-related processing.