Strategic Retrieval Research Articles

Strategic retrieval processing and the impact of knowing when a memory was first created

Retrieval orientation refers to a process where participants strategically alter how a memory cue is processed in response to different task demands. In the present study we explored whether retrieval orientation is influenced by knowing when an old stimulus was first encoded. Participants completed separate remember/know test blocks for old items from a recent delay (40min) and old items from a remote delay (48h). Manipulations at encoding ensured that performance levels were matched between these two blocks, thus avoiding confounds with differences in retrieval effort. Importantly, a third test block comprised old items from both delays randomly intermixed. As the nature of the old items varies unpredictably in the mixed block, it should not be possibly to adopt a specific retrieval orientation and the mixed block therefore acts as a control condition. Participants saw the words “mixed,” “recent” or “remote” prior to each test block. Comparing ERPs from the recent and remote blocks permitted an investigation of whether participants alter their retrieval orientation in response to the specific length of the retention interval. Comparing ERPs from the pure (recent and remote) test blocks to ERPs from the mixed block permitted an investigation of whether delay information per se led to differences in retrieval strategy. Analysis of the ERP data found no differences between the recent and remote blocks. However, ERPs from these pure blocks were significantly less positive than ERPs from the mixed block from 200ms towards the end of the epoch. The findings suggest that the delay information was useful in a general sense and encouraged retrieval strategies distinct from those engaged in the mixed block. We speculate that such strategies might relate to whether or not the retrieval search is specific and constrained and/or whether processes that serve to reinstate the original encoding context are engaged.

Autobiographical episodic memory in major depressive disorder.

Autobiographical memory in major depression has been characterized as overgeneralized, with patients recalling few episodic details, prioritizing general schematic events. However, whether this effect reflects impaired episodic or semantic memory, or domain-general cognitive processes, is unknown. We used the Autobiographical Interview (Levine, Svoboda, Hay, Winocur, & Moscovitch, 2002) to derive episodic and semantic contributions to autobiographical memory in patients with severe major depression. We also assessed memory for public events and famous people. Depressed patients were impaired on episodic, but not semantic, autobiographical memory from 2 weeks to 10 years before testing. They were also impaired on memory for public events, possibly because they followed the news less than controls. Patients' memory for famous names was not impaired, although this was strongly associated with non-episodic memories to a greater degree than in controls. The findings suggest a specific impairment of episodic autobiographical memory in depression that is not fully accounted for by domain-general processes involved in strategic retrieval.

Executive functions are employed to process episodic and relational memories in children with autism spectrum disorders.

Objective: Long-term memory functioning in autism spectrum disorders (ASDs) is marked by a characteristic pattern of impairments and strengths. Individuals with ASD show impairment in memory tasks that require the processing of relational and contextual information, but spared performance on tasks requiring more item-based, acontextual processing. Two experiments investigated the cognitive mechanisms underlying this memory profile. Method: A sample of 14 children with a diagnosis of high-functioning ASD (age: M = 12.2 years), and a matched control group of 14 typically developing (TD) children (age: M = 12.1 years), participated in a range of behavioral memory tasks in which we measured both relational and item-based memory abilities. They also completed a battery of executive function measures. Results: The ASD group showed specific deficits in relational memory, but spared or superior performance in item-based memory, across all tasks. Importantly, for ASD children, executive ability was significantly correlated with relational memory but not with item-based memory. No such relationship was present in the control group. This suggests that children with ASD atypically employed effortful, executive strategies to retrieve relational (but not item-specific) information, whereas TD children appeared to use more automatic processes. Conclusions: The relational memory impairment in ASD may result from a specific impairment in automatic associative retrieval processes with an increased reliance on effortful and strategic retrieval processes. Our findings allow specific neural predictions to be made regarding the interactive functioning of the hippocampus, prefrontal cortex, and posterior parietal cortex in ASD as a neural network supporting relational memory processing.

Mechanism of disorientation: Reality filtering versus content monitoring

Disorientation is frequent after brain damage. It is a constituent component of post-traumatic amnesia and was part of the original definition of the Korsakoff syndrome, together with amnesia and confabulations. Orbitofrontal reality filtering is a pre-conscious memory control process that has been held accountable for disorientation and a specific type of confabulations that patients act upon. A recent study questioned the specificity of this process and suggested that confabulating patients who failed in orbitofrontal reality filtering similarly failed to monitor the precise content of memories, a critical step within the strategic retrieval account, which describes a series of processes leading up to the recollection of memories. In the present study we combined the proposed experimental requirements of both processes in a single continuous recognition task and tested a group of 21 patients with a matched deficit of delayed free recall. We found that only deficient reality filtering, but not content monitoring, significantly correlated with disorientation and distinguished between confabulators and non-confabulators. Thus, reality confusion, as evident in disorientation and behaviourally spontaneous confabulation, primarily reflects an inability to monitor memories' relation with ongoing reality rather than to monitor their precise content.

The influence of directed attention at encoding on source memory retrieval in the young and old: An ERP study

Neuroimaging evidence suggests that older adults exhibit deficits in frontally-mediated strategic retrieval processes, such as post-retrieval monitoring. Behavioral research suggests that explicitly directing attention toward source features during encoding may improve source memory for both young and older adults and alleviate age-related source memory impairments, in part, by reducing demands on post-retrieval monitoring. We investigated this hypothesis in the present event-related potential (ERP) study. Young and older adults attended to either objects and their presented color (source) or to the object alone during study and made color source memory decisions at test. We attempted to match performance between groups by halving the memory load for older adults. Behavioral results showed that, while direction of attention to object and color improved source memory for both groups, older adults benefited less than the young. ERPs revealed that demands on late right frontal effects, indicative of post-retrieval monitoring, were similarly reduced by directed attention at encoding for both groups. However, older adults showed reduced ERP correlates of recollection (parietal old–new effect), as well as a sustained widespread negativity, potentially indicative of memory searches for perceptual details in the face of impaired recollection. These results suggest that older adults, like the young, can engage in post-retrieval monitoring when source details are difficult to recover. However, impaired recollection may underlie persistent age-related source memory deficits, even when encoding is supported via directed attention.

Growing Up with Asperger’s Syndrome: Developmental Trajectory of Autobiographical Memory

Autobiographical memory (AM) and social cognition share common properties and both are affected in autism spectrum disorders (ASD). So far, most of the scant research in ASD has concerned adults, systematically reporting impairment of the episodic component. The only study to be conducted with children concluded that they have poorer personal semantic knowledge than typical developing children. The present study explores the development of both components of AM in an 8-year-old boy diagnosed with Asperger’s syndrome, based on three examinations in 2007, 2008, and 2010. On each occasion, he underwent a general neuropsychological assessment including theory of mind (ToM) tasks, and a specially designed AM task allowing us to test both the semantic and the episodic components for three lifetime periods (current year, previous year, and earlier years). We observed difficulties in strategic retrieval and ToM, with a significant improvement between the second and third examinations. Regarding AM, different patterns of performance were noted in all three examinations: (1) relative preservation of current year personal knowledge, but impairment for the previous and earlier years, and (2) impairment of episodic memory for the current and previous year, but performances similar to those of controls for the earlier years. The first pattern can be explained by abnormal forgetting and by the semanticization mechanism, which needs verbal communication and social interaction to be efficient. The second pattern suggests that the development of episodic memory only reached the stage of “event memory.” This term refers to memory for personal events lacking in details or spatiotemporal specificity, and is usually observed in children younger than five. We conclude that the abnormal functioning of social cognition in ASD, encompassing social, and personal points of view, has an impact on both components of AM.

Strategic retrieval and retrieval orientation in reality monitoring studied by event-related potentials (ERPs)

Reality monitoring requires the differentiation between perceived and imagined events or between our own actions and the actions of others. The role of control processes in reality monitoring is yet not fully understood. In the current event-related potential (ERP) study, we investigated such control processes in the form of retrieval orientation and strategic retrieval of nontarget information. At study, complete or incomplete object words were presented in sentences. Participants had to identify the words as the subject of the sentence (perceive condition) or had to complete them upon presentation of a word fragment (self-generate condition). The participants' memory accuracy was better for generated items than for perceived items, as tested in a subsequent memory exclusion task. Comparison of ERPs to new items between the two test conditions (i.e. assessing retrieval orientation) showed more positive ERPs when generated object names were targeted. Retrieval orientation also modulated the early midfrontal old/new effect: Items of the self-generate condition elicited this effect irrespective of their target/nontarget status, while in response to the less well remembered items of the perceive condition it was only found when these items were defined as targets. Target retrieval (as reflected in the left-parietal old/new effect) occurred in both test conditions, but nontarget retrieval was observed only for generated items (when perceived items were targeted). Current findings indicate that retrieval orientation can modulate familiarity-related processes. The selective occurrence of nontarget retrieval for generated items corroborates the concept that the ease with which nontarget information can be accessed promotes nontarget retrieval.

Why do ideas get more creative across time? An executive interpretation of the serial order effect in divergent thinking tasks.

The serial order effect—the tendency for later responses to a divergent thinking task to be better than earlier ones—is one of the oldest and most robust findings in modern creativity work. But why do ideas get better? Using new methods that afford a fine-grained look at temporal trajectories, we contrasted two explanations: the classic spreading activation account and a new account based on executive and strategic aspects of creative thought. After completing measures of fluid intelligence and personality, a sample of young adults (n = 133) completed a 10-min unusual uses task. Each response was time-stamped and then rated for creativity by three raters. Multilevel structural equation models estimated the trajectories of creativity and fluency across time and tested if intelligence moderated the effects of time. As in past work, creativity increased sharply with time and flattened slightly by the task's end, and fluency was highest in the task's first minute and then dropped sharply. Intelligence, however, moderated the serial order effect—as intelligence increased, the serial order effect diminished. Taken together, the findings are more consistent with a view that emphasizes executive processes, particularly processes involved in the strategic retrieval and manipulation of knowledge, than the simple spreading of activation to increasingly remote concepts.

Declarative memory disorders in patients with brain tumors can improve after cognitive training intervention: evidence from functional MRI

I read with great interest the recent paper published in Journal of Neuro-Oncology by Carlesimo [1]. The author proposed that declarative memory disorders in tumor patients could be identified even when the Papez circuit is not directly involved. It was suggested that attentional and executive impairments following frontal lobe involvement could produce these deficits because of disconnection of the frontal cortical areas from inputs arriving from other cortical and subcortical brain regions including the Papez circuit. The author also suggested that, although failure of the storage mechanisms generally precludes restorative interventions, deficits in the attentional, executive, and working memory mechanisms underlying encoding of information and the strategic retrieval of stored information can ‘‘likely’’ be re-educated and lead to improved declarative memory functioning. We have just published a study showing evidence of this hypothesis in tumor patients [2]. In this study, the brain correlates of strategic memory training were investigated in patients with primary tumors in the prefrontal cortex (PFC) using functional magnetic resonance imaging (fMRI) and cognitive tests. Twenty-one adult patients with postoperative lesions in the PFC (oligodendrogliomas, astrocytomas, meningiomas), 12 in the left dorsolateral PFC (LPFC) and 9 in the bilateral orbitofrontal cortex (BOFC), at least 6 months after surgery, were assessed before and after semantic strategy training using a verbal memory encoding paradigm during fMRI scanning. We used a within-subject design with no healthy controls. After cognitive training, both groups of patients showed significant improvement in declarative episodic verbal memory and use of semantic strategy. In the LPFC group, greater activity in left inferior and medial frontal gyrus (perilesional areas), precentral gyrus, and insula was found after training. For the BOFC group, higher activation was found in the left parietal cortex, right cingulate, and precuneus after training (new brain areas outside the usual episodic memory network). The activation of these specific areas within the memory and executive networks including perilesional and new brain areas following cognitive training was associated with compensatory brain mechanisms [3]. To our knowledge, this was the first description of patients with declarative memory disorders following PFC primary brain tumor lesions showing improvement in declarative memory after cognitive training associated with compensatory brain mechanisms. These findings corroborate the hypothesis described in Carlesimo’s article [1] of possible improvement and benefit from strategic memory training in patients with declarative episodic memory impairments due to cerebral tumors. Since a high prevalence of memory deficits is found in patients with cerebral tumors related to the effects of tumor mass, edema or as result of surgical, chemotherapy, and radiotherapy treatments, cognitive rehabilitation interventions could be of great value in management of such patients.

Recall deficits in stroke patients with thalamic lesions covary with damage to the parvocellular mediodorsal nucleus of the thalamus

The functional role of the mediodorsal thalamic nucleus (MD) and its cortical network in memory processes is discussed controversially. While Aggleton and Brown (1999) suggested a role for recognition and not recall, Van der Werf et al. (2003) suggested that this nucleus is functionally related to executive function and strategic retrieval, based on its connections to the prefrontal cortices (PFC). The present study used a lesion approach including patients with focal thalamic lesions to examine the functions of the MD, the intralaminar nuclei and the midline nuclei in memory processing. A newly designed pair association task was used, which allowed the assessment of recognition and cued recall performance.Volume loss in thalamic nuclei was estimated as a predictor for alterations in memory performance. Patients performed poorer than healthy controls on recognition accuracy and cued recall. Furthermore, patients responded slower than controls specifically on recognition trials followed by successful cued recall of the paired associate. Reduced recall of picture pairs and increased response times during recognition followed by cued recall covaried with the volume loss in the parvocellular MD. This pattern suggests a role of this thalamic region in recall and thus recollection, which does not fit the framework proposed by Aggleton and Brown (1999). The functional specialization of the parvocellular MD accords with its connectivity to the dorsolateral PFC, highlighting the role of this thalamocortical network in explicit memory (Van der Werf et al., 2003).

Event-related potential evidence for separable automatic and controlled retrieval processes in proactive interference

Interference between competing memories is a major source of retrieval failure, yet, surprisingly little is known about how competitive memory activation arises in the brain. One possibility is that interference during episodic retrieval might be produced by relatively automatic conceptual priming mechanisms that are independent of strategic retrieval processes. Such priming-driven interference might occur when the competing memories have strong pre-existing associations to the retrieval cue. We used ERPs to measure the neural dynamics of retrieval competition, and investigated whether the ERP correlates of interference were affected by varying task demands for selective retrieval. Participants encoded cue words that were presented either two or four times, paired either with the same or different strongly associated words across repetitions. In a subsequent test, participants either selectively recalled each cue's most recent associate, or simply judged how many times a cue had been presented, without requiring selective recall. Interference effects on test performance were only seen in the recall task. In contrast, ERPs during test revealed an early posterior positivity for high interference items that was present in both retrieval tasks. This early ERP effect likely reflects a conceptual priming-related N400 reduction when many associations to a cue were pre-activated. A later parietal positivity resembling the ERP correlate of conscious recollection was found only in the recall task. The results suggest that early effects of proactive interference are relatively automatic and independent of intentional retrieval processes, consistent with suggestions that interference can arise through conceptual priming.

Memory disorders in patients with cerebral tumors

In patients with cerebral tumors, deficits in declarative episodic memory typically result from damage to structures of the Papez circuit. These deficits can arise directly from the action of the tumor mass or indirectly from the surgical intervention. Memory deficits are also frequently seen in patients who show no direct involvement of the Papez circuit. In these patients, the memory impairment probably results from disruption of frontal lobe functioning (caused by localization of the tumor at this level or disconnection from subcortical afferents). Here, I review the neuropsychological tools used to differentiate amnesic syndromes resulting from lack of consolidation of new memory traces (as a consequence of damage to the Papez circuit) from amnesias resulting from reduced efficiency of elaborative encoding and/or strategic retrieval processes (as a consequence of frontal lobe damage). The clinical and rehabilitative implications of this distinction are briefly discussed.

Interference from retrieval cues in Parkinson's disease.

Existing studies on memory interference in Parkinson's disease (PD) patients have provided mixed results and it is unknown whether PD patients have problems in overcoming interference from retrieval cues. We investigated this issue by using a part-list cuing paradigm. In this paradigm, after the study of a list of items, the presentation of some of these items as retrieval cues hinders the recall of the remaining ones. We tested PD patients' (n = 19) and control participants' (n = 16) episodic memory in the presence and absence of part-list cues, using initial-letter probes, and following either weak or strong serial associative encoding of list items. Both PD patients and control participants showed a comparable and significant part-list cuing effect after weak associative encoding (13% vs. 12% decrease in retrieval in part-list cuing vs. no part-list cuing -control- conditions in PD patients and control participants, respectively), denoting a similar effect of cue-driven interference in the two populations when a serial retrieval strategy is hard to develop. However, only PD patients showed a significant part-list cuing effect after strong associative encoding (20% vs. 5% decrease in retrieval in patients and controls, respectively). When encoding promotes the development of an effective serial retrieval strategy, the presentation of part-list cues has a specifically disruptive effect in PD patients. This indicates problems in strategic retrieval, probably related to PD patients' increased tendency to rely on external cues. Findings in control conditions suggest that less effective encoding may have contributed to PD patients' memory performance.

Differential Impairment of Remembering the Past and Imagining Novel Events after Thalamic Lesions

Vividly remembering the past and imagining the future (mental time travel) seem to rely on common neural substrates and mental time travel impairments in patients with brain lesions seem to encompass both temporal domains. However, because future thinking-or more generally imagining novel events-involves the recombination of stored elements into a new event, it requires additional resources that are not shared by episodic memory. We aimed to demonstrate this asymmetry in an event generation task administered to two patients with lesions in the medial dorsal thalamus. Because of the dense connection with pFC, this nucleus of the thalamus is implicated in executive aspects of memory (strategic retrieval), which are presumably more important for future thinking than for episodic memory. Compared with groups of healthy matched control participants, both patients could only produce novel events with extensive help of the experimenter (prompting) in the absence of episodic memory problems. Impairments were most pronounced for imagining personal fictitious and impersonal events. More precisely, the patients' descriptions of novel events lacked content and spatio-temporal relations. The observed impairment is unlikely to trace back to disturbances in self-projection, scene construction, or time concept and could be explained by a recombination deficit. Thus, although memory and the imagination of novel events are tightly linked, they also partly rely on different processes.

The Organisation of Mind

The ventral medial prefrontal cortex (vmPFC) has long been implicated in monitoring of memory veracity, and more recently also in memory schema functions. In our model of strategic retrieval the two are related. We have proposed that the vmPFC has two schema-dependent functions: (i) to establish context-relevant templates against which the output of memory systems can be compared; (ii) to mediate automatic decision monitoring processes to ensure that only those responses that meet the criterion are enacted. Electroencephalogram (EEG) data were used to provide evidence that vmPFC supports both functions, and that schema instantiation informs monitoring. Participants viewed pictures of acquaintances, along with those of famous and nonfamous people, and were asked to respond positively only to pictures of individuals they had met (personal familiarity). The Self serves as a super-ordinate cognitive schema, facilitating accurate endorsement of acquaintances and exclusion of non-personal but familiar faces. For the present report we focused on pre-cue tonic oscillatory activity. Controls demonstrated theta coherence desynchronization between medial prefrontal areas, inferotemporal and lateral temporal cortices. These oscillatory coherence patterns were significantly reduced in patients with vmPFC damage, especially in those with clinical histories of spontaneous confabulation. Importantly, these pre-stimulus cortico-cortical desynchronizations predicted post-cue automatic memory activation, as indexed by a familiarity modulation of the face-sensitive posterior cortical N170. Pre-cue desynchronization also predicted early post-cue frontal positive modulation (P230) and response accuracy. The data are consistent with a schema instantiation model that suggests the vmPFC biases posterior neocortical long-term memory representations that enhance automatic memory cue processing and informs frontally-mediated rapid memory monitoring (P230). Damage to these structures can lead to inaccurate, context-irrelevant activation of schemas. These, in turn, impair monitoring signals and can lead to confabulation when memory control processes are also deficient.

“It's a hair-dryer…No, it's a drill”: Misidentification-related false recognitions in younger and older adults

Memory for visual objects, although typically highly accurate, can be distorted, especially in older adults. Here we asked whether also erroneous identifications of visual objects subsequently corrected and replaced by a correct identification might induce false recognitions, and whether this is more likely to occur in older people. For this aim a new paradigm was developed. In the first phase, participants performed a visual object identification task with degraded pictures of objects and produced correct and false but subsequently corrected identifications. In the second phase, participants performed a surprise recognition task in which also false identifications were presented. False identifications elicited false recognitions, with a stronger and more reliable effect in elderly participants, suggesting that correcting the initial visual error is not sufficient to correct the memory for the experience. Moreover, misidentification-related false recognitions coexisted in memory along with correct recognitions of correct identifications. These findings are discussed in relation with age-related deficits in memory updating and strategic retrieval.

Strategic retrieval in a reality monitoring task

Strategic recollection refers to control processes that allow the retrieval of information that is relevant for a specific situation. These processes can be studied in memory exclusion tasks, which require the retrieval of particular kinds of episodic information. In the current study, we investigated strategic recollection in reality monitoring by event-related potentials (ERPs). Participants studied object words, followed by a picture of the denoted object (perceive condition) or followed by the instruction to imagine such a picture (imagine condition). At test, subjects had to identify words of one study condition and to reject words of the second study condition together with newly presented items. Data analysis showed that object names were better identified when items of the perceive condition were targeted. In this test condition, a left parietal old/new effect (the ERP correlate of recollection) was observed only in response to targets. In contrast, both targets and nontargets elicited this old/new effect when items of the imagine condition were targeted. The magnitude of the left parietal old/new effect to nontargets in this condition (but no other left parietal old/new effect) correlated positively with the discrimination indices of both test conditions. In addition, ERPs to targets and nontargets differed at right frontal electrode sites at longer latencies (1500–1800 ms), with more positive ERPs for targets. Findings indicate that subjects retrieved nontarget information in the more difficult task condition, while they relied on target information alone in the less difficult task. This kind of strategic retrieval was not mirrored in other old/new effects. The correlation between the left parietal old/new effect for nontargets in the imagined item target condition and the discrimination indices of both conditions may indicate that the ease of nontarget retrieval, rather than the difficulty of target retrieval, increases the likelihood that nontarget information is actually retrieved.

Profiles of recent autobiographical memory retrieval in semantic dementia, behavioural-variant frontotemporal dementia, and Alzheimer's disease

Episodic autobiographical memory (ABM) comprises recollection for events that are grounded within a specific spatiotemporal context, and usually accompanied by perceptual and emotional information. The neural substrates mediating ABM retrieval are those harbouring significant pathology in semantic dementia (SD) and behavioural-variant frontotemporal dementia (bvFTD), the most common subtypes of FTD. Relatively little is known, however, regarding the differential patterns of contextual details during episodic ABM retrieval across these dementia syndromes. This study investigated episodic ABM retrieval under free and probed recall conditions from 4 time periods with the aim to identify disease-specific profiles of episodic ABM contextual details. Episodic ABM was measured in 25 SD and 15 bvFTD patients and their performance contrasted to that of 17 Alzheimer's disease (AD) patients and 19 age-matched controls. Critically, SD patients showed relatively preserved recent ABM in comparison with remote epochs. In contrast, bvFTD and AD patients showed a reduced capacity to recall specific and contextually rich ABMs across all life epochs, in both free and probed recall conditions. Analyses of the recent period (last 12 months) provided evidence for different profiles of contextual episodic details recalled in dementia syndromes. Following probing, SD patients’ recall deficits emanated exclusively from compromised Emotion/Thoughts and Spatiotemporal details. In contrast, bvFTD patients were significantly impaired across all categories of contextual details whereas AD patients showed deficits for Event and Emotion/Thoughts details only. As the largest study of ABM in FTD to date, these findings emphasise the differential impairment of recent ABM contextual details contingent on the underlying disease pathology. In addition, these results point towards the importance of investigating the constituent elements of emotion processing and strategic retrieval processes as potential variables mediating recent episodic ABM retrieval.

Verbal Fluency in Spanish-Speaking Children: Analysis Model According to Task Type, Clustering, and Switching Strategies and Performance Over Time

Verbal fluency (VF) tasks are extensively used to measure strategic retrieval and executive functioning. Results for total production of words, clustering and switching strategies, and performance over time for Spanish-speaking children are provided. A total of 120 children, ranging in age from 8 to 11, were divided by age into two groups and evaluated. A higher total score for words produced in the semantic compared with the phonological task, a correlation between clustering and switching strategies and total score, and decreased task performance over time were evidenced. These scores were higher in the older group. Moreover, an association was found between verbal fluency tasks, strategies employed, and cognitive executive functions. This indicates that clustering and switching strategies provide indicators of strategic retrieval and executive processes. Together the results suggest that these fluency scores are valuable to measure underlying cognitive processes and retrieval strategies and therefore could be useful to assess executive function deficits in children.

Multimodal Imaging of Incidental Retrieval: The Low Route to Memory

Memories of past episodes frequently come to mind incidentally, without directed search. It has remained unclear how incidental retrieval processes are initiated in the brain. Here we used fMRI and ERP recordings to find brain activity that specifically correlates with incidental retrieval, as compared to intentional retrieval. Intentional retrieval was associated with increased activation in dorsolateral prefrontal cortex. By contrast, incidental retrieval was associated with a reduced fMRI signal in posterior brain regions, including extrastriate and parahippocampal cortex, and a modulation of a posterior ERP component 170 msec after the onset of visual retrieval cues. Successful retrieval under both intentional and incidental conditions was associated with increased activation in the hippocampus, precuneus, and ventrolateral prefrontal cortex, as well as increased amplitude of the P600 ERP component. These results demonstrate how early bottom-up signals from posterior cortex can lead to reactivation of episodic memories in the absence of strategic retrieval attempts.