Brain regions associated with successful and unsuccessful retrieval of verbal episodic memory as revealed by divided attention (original) (raw)
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Hippocampus, 2004
Lesion studies have provided compelling evidence that episodic memory is dependent on the integrity of the medial temporal lobe (MTL). This role of the MTL in episodic memory has been supported by several neuroimaging studies during both episodic encoding and retrieval. After two meta-analyses of positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) studies, we investigated a possible dissociation within the MTL memory system in relation to encoding and retrieval processes. Based on previous reports that specifically related the function of the MTL in episodic memory to successful encoding and actual recovery of information, we applied event-related fMRI to compare successful encoding of words (ES) directly with successful recognition of those same words (RS). Our results did not indicate a clear dissociation between encoding and retrieval activations in the MTL. Instead, a region in the left MTL, covering the parahippocampal cortex and hippocampal formation, which was activated during ES almost completely overlapped with the area that was activated during RS. An additional region in the left anterior MTL, including the entorhinal cortex, was found to be activated exclusively during ES. Research has indicated that a large percentage of cells in this region are particularly sensitive to the relative novelty of stimuli. Our results, therefore, suggest that the parahippocampal/hippocampal region is involved in the formation and subsequent reactivation of memory traces, whereas the activity observed in the entorhinal cortex may reflect elementary memory processes related to novelty detection. © 2003 Wiley-Liss, Inc.
Brain, 1999
Though the right prefrontal cortex is often activated in neuroimaging studies of episodic memory retrieval, the functional significance of this activation remains unresolved. In this functional MRI study of 12 healthy volunteers, we tested the hypothesis that one role of the right prefrontal cortex is to monitor the information retrieved from episodic memory in order to make an appropriate response. The critical comparison was between two word recognition tasks that differed only in whether correct responses did or did not require Abbreviations: BA ϭ Brodmann area; BOLD ϭ blood oxygenation level-dependent; fMRI ϭ functional MRI
Neuroanatomical correlates of retrieval in episodic memory: auditory sentence recognition
Proceedings of the National Academy of Sciences, 1994
This study used positron emission tomography (PET) to investigate the neuroanatomical correlates of remembering previously experienced events. Twelve young healthy adults listened to "old" meaningful sentences which they had studied 24 hr previously. As a control task the subjects listened to comparable "new" sentences that they had never heard before. Regional cerebral blood flow associated with each task was measured by PET scans using 150-labeled water.
Brain systems for encoding and retrieval of auditory—verbal memory. An in vivo study in humans
Brain, 1995
Long-term auditory-verbal memory comprises, at a neuropsychological level, a number of distinct cognitive processes. In the present study we determined the brain systems engaged during encoding (experiment I) and retrieval {experiment 2) of episodic auditory-verbal material. In the separate experiments, PET measurements of regional cerebral blood flow (rCBF), an index of neural activity, were performed in normal volunteers during either the encoding or the retrieval of paired word associates. In experiment 1, a dual task interference paradigm was used to isolate areas involved in episodic encoding from those which would be concurrently activated by other cognitive processes associated with the presentation of paired associates, notably priming. In experiment 2, we used the cued retrieval of paired associates from episodic or from semantic memory in order to isolate Keywords: PET; episodic memory; encoding; retrieval the neural correlates of episodic memories. Encoding of episodic memory was associated with activation of the left prefrontal cortex and the retrosplenial area of the cingulate cortex, while retrieval from episodic memory was associated with activation of the precuneus bilaterally and of the right prefrontal cortex. These results are compatible with the patterns of activation reported in a previous PET memory experiment in which encoding and retrieval were studied concurrently. They also indicate that separate brain systems are engaged during the encoding and retrieval phases of episodic auditory-verbal memory. Retrieval from episodic memory engages a different, but overlapping, system to that engaged by retrieval from semantic memory, a finding that lends functional anatomical support to this neuropsychological distinction.
Brain, 1998
Functional neuroimaging studies of episodic recognition memory consistently demonstrate retrieval-associated activation in right prefrontal regions, including the right anterior and right dorsolateral prefrontal cortices. In theory, these activations could reflect processes associated with retrieval success, retrieval effort or retrieval attempt; each of these hypotheses has some support from previous studies. In Experiment 1, we examined these functional interpretations using functional MRI to measure prefrontal activation across multiple levels of recognition performance. Results revealed similar patterns of right prefrontal activation across varying levels of retrieval success and retrieval effort, suggesting that these activations reflect retrieval attempt. Retrieval attempt may include initiation of retrieval search or evaluation of the products of retrieval, such as scrutiny of specific attributes of the test item in an effort to determine whether it was encountered previously. In Experiment 2, we examined whether engagement of retrieval attempt is Abbreviations: AC ϭ anterior commissure; ANOVA ϭ analysis of variance; APC ϭ anterior prefrontal cortex; BA ϭ Brodmann area; DLPC ϭ dorsolateral prefrontal cortex; ERP ϭ event-related potential; fMRI ϭ functional MRI; rCBF ϭ regional cerebral blood flow
2004
Prior work has shown that when responses to incidentally encoded words are sorted, subsequently remembered words elicit greater left prefrontal BOLD signal change relative to forgotten words. Similarly, low-frequency words elicit greater activation than highfrequency words in the same left prefrontal regions, contributing to their better subsequent memorability. This study examined the relative contribution of encoding and retrieval processes to the correct recognition of target words. A mixture of high-and lowfrequency words was incidentally encoded. Scanning was performed at encoding as well as during retrieval. During encoding, greater activation in the left prefrontal and anterior cingulate regions predicted a higher proportion of hits for low-frequency words. However, data acquired during recognition showed that word frequency did not modulate activation in any of the areas tracking successful recognition. This result demonstrates that under some circumstances, the recognition of studied words is determined purely by processes that are active during encoding. In contrast to the finding for hits, activation associated with correctly rejected foils was modulated by word frequency, being higher for high-frequency words in the left lateral parietal and anterior prefrontal regions. These findings were replicated in two further experiments, one in which the number of test items at recognition was doubled and another where encoding strength for high-frequency words was varied (once vs. 10 times). These results indicate that word frequency modulates activity in the left lateral parietal and anterior prefrontal regions contingent on whether the item involved is correctly recognized as a target or a foil. This observation is consistent with a dual process account of episodic memory.
The investigation of memory function using functional magnetic resonance imaging (fMRI) is an expanding field of research. The aim of this study was to demonstrate brain-activity patterns related to a word-pair association task employing a whole-brain EPI sequence. Six right-handed, healthy male volunteers (mean age: 27.5 years) took part in the study. fMRI was performed at a field strength of 1.5 Tesla with 26–32 slices parallel to the AC-PC line, depending on individual brain size. Distributed brain regions were activated in episodic encoding and retrieval with similarities, but also (distinct) differences in activation patterns. Bilateral prefrontal cortical areas were involved when comparing encoding as well as retrieval to the reference condition (nonsense words). Furthermore, activation was observed in cerebellar areas during encoding, and activation in bilateral parietal areas (precuneus and inferior parietal cortex) was differentially more pronounced during retrieval. The activation of left dorsomedial thalamus during retrieval of high imagery-content word-pair associates may point to the role of this structure in episodic retrieval. The direct cognitive subtraction of encoding minus retrieval yielded a differentially larger left prefrontal activation. There was a differentially higher right prefrontal activation during retrieval than during encoding, underlining the proposed right/left asymmetry for episodic memory processes.
Journal of Cognitive Neuroscience, 2003
& We propose a new hypothesis concerning the lateralization of prefrontal cortex (PFC) activity during verbal episodic memory retrieval. The hypothesis states that the left PFC is differentially more involved in semantically guided information production than is the right PFC, and that the right PFC is differentially more involved in monitoring and verification than is the left PFC. This ''production-monitoring hypothesis'' differs from the existing ''systematic -heuristic hypothesis,'' which proposes that the left PFC is primarily involved in systematic retrieval operations, and the right PFC in heuristic retrieval operations. To compare the two hypotheses, we measured PFC activity using positron emission tomography (PET) during the performance of four episodic retrieval tasks: stem cued recall, associative cued recall, context recognition (source memory), and item recognition. Recall tasks emphasized production processes, whereas recognition tasks emphasized monitoring processes. Stem cued recall and context-recognition tasks underscored systematic operations, whereas associative cued recall and item-recognition tasks underscored heuristic oper-ations. Consistent with the production-monitoring hypothesis, the left PFC was more activated for recall than for recognition tasks and the right PFC was more activated for recognition than for recall tasks. Inconsistent with the systematic -heuristic hypothesis, the left PFC was more activated for heuristic than for systematic tasks and the right PFC showed the converse result. Additionally, the study yielded activation differences outside the PFC. In agreement with a previous recall/ recognition PET study, anterior cingulate, cerebellar, and striatal regions were more activated for recall than for recognition tasks, and the converse occurred for posterior parietal regions. A right medial temporal lobe region was more activated for stem cued recall and context recognition than for associative cued recall and item recognition, possibly reflecting perceptual integration. In sum, the results provide evidence for the production-monitoring hypothesis and clarify the role of different brain regions typically activated in PET and functional magnetic resonance imaging (fMRI) studies of episodic retrieval. &
The Role of the Prefrontal Cortex in Recognition Memory and Memory for Source: An fMRI Study
NeuroImage, 1999
We employed fMRI to index neural activity in prefrontal cortex during tests of recognition and source memory. At study, subjects were presented with words displayed either to the left or right of fixation, and, depending on the side, performed one of two orienting tasks. The test phase consisted of a sequence of three 10-word blocks, displayed in central vision. For one block, subjects performed recognition judgements on a mixture of two old and eight new words (low density recognition). For another block, recognition judgements were performed on a mixture of eight old and two new words (high density recognition). In the remaining block, also consisting of eight old and two new items, the requirement was to judge whether each word had been presented at study on the left or the right. Relative to the low density condition, high density recognition was associated with increased activity in right and, to a lesser extent, left, anterior prefrontal cortex (BA 10), replicating the findings of two previous PET studies. Right anterior prefrontal activity did not show any further increase during the source task. Instead, greater activity was found, relative to high density recognition, in left BA 10, left inferior frontal gyrus (BA 45/47), and bilateral opercular cortices (BA 45/47). The findings are inconsistent with the proposal that activation of right anterior prefrontal cortex during memory retrieval reflects ''postretrieval'' processing demands, such demands being considerably greater for judgments of source than recognition. The findings provide further evidence that the left prefrontal cortex plays a role in episodic memory retrieval when the task explicitly requires recovery of contextual as well as item information.