Right prefrontal cortex and episodic memory retrieval: a functional MRI test of the monitoring hypothesis (original) (raw)

Prefrontal cortex and recognition memory. Functional-MRI evidence for context-dependent retrieval processes

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

Functional MRI of cerebral activation during encoding and retrieval of words

Human Brain Mapping, 1999

The aims of the present study were to identify the cerebral structures associated with encoding and retrieval of verbal material. To circumvent the inherent disadvantages of the conventional block designs used in functional magnetic resonance imaging (MRI), an event-related design compared activation related to randomly intermixed old and new words during recognition. To support the validity of results, both nonparametric analyses in regions of interest (ROI) and statistical parametric mapping (SPM 96) were used. Twelve healthy volunteers, ages 22-35 years, performed three tasks: intentional encoding of words, recognition of old (previously learned) words, and discrimination between words and nonwords, a task to control for visual input and motor output during recognition. Echo-planar magnetic resonance imaging of bloodlevel, oxygen-dependent, task-related changes was used to compare cerebral activity under active and resting conditions as well as to detect event-related activity within blocks of trials. Comparable results were obtained following nonparametric statistical analysis of selected ROI and SPM. Encoding of words was associated with increased activity in the left inferior frontal gyrus, including Broca's area and in the left parietal association cortex. Event-related data analysis revealed activation of the right medial frontal gyrus, the right anterior cingulate gyrus, and parietal association cortices during recognition of previously presented words. In the lexical decision task, words in comparison with nonwords were associated with activation of the left parietal association cortex. The right medial frontal gyrus, the right anterior cingulate gyrus, and the right parietal association cortex are likely to be involved in episodic memory functions during recognition of previously presented verbal material. The comparison of event-related activation occurring within one trial block instead of among several trial blocks may significantly improve the performance of memory studies.

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.

Common pathway in the medial temporal lobe for storage and recovery of words as revealed by event-related functional MRI

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.

Heun, R. et al. Functional MRI of cerebral activation during encoding and retrieval of words. Hum. Brain Mapp. 8, 157-169

Human Brain Mapping

The functional roles of prefrontal cortex in episodic memory. I. Encoding

Brain, 1998

Functional neuroimaging studies of memory retrieval show consistent activation of the right prefrontal and superior parietal cortex. We examined the specific role of the prefrontal cortex during retrieval with the hypothesis that this region mediates monitoring processes necessary for optimal recall. During functional neuroimaging with PET, subjects retrieved verbal material under two conditions. In the first, an organizational structure had been provided, prior to scanning, and this formed the basis for a monitored memory search while the scan took place. A comparison condition did not require a monitored search because recall was externally cued. In both conditions, when compared with baseline tasks prefrontal cortex and

Semantic encoding and retrieval in the left inferior prefrontal cortex: a functional MRI study of task difficulty and process specificity

The Journal of neuroscience : the official journal of the Society for Neuroscience, 1995

Prefrontal cortical function was examined during semantic encoding and repetition priming using functional magnetic resonance imaging (fMRI), a noninvasive technique for localizing regional changes in blood oxygenation, a correlate of neural activity. Words studied in a semantic (deep) encoding condition were better remembered than words studied in both easier and more difficult nonsemantic (shallow) encoding conditions, with difficulty indexed by response time. The left inferior prefrontal cortex (LIPC) (Brodmann's areas 45, 46, 47) showed increased activation during semantic encoding relative to nonsemantic encoding regardless of the relative difficulty of the nonsemantic encoding task. Therefore, LIPC activation appears to be related to semantic encoding and not task difficulty. Semantic encoding decisions are performed faster the second time words are presented. This represents semantic repetition priming, a facilitation in semantic processing for previously encoded words th...

Prefrontal cortex and episodic memory retrieval mode

Proceedings of the National Academy of Sciences, 2000

A multistudy analysis of positron emission tomography data identified three right prefrontal and two left prefrontal cortical sites, as well as a region in the anterior cingulate gyrus, where neuronal activity is correlated with the maintenance of episodic memory retrieval mode (REMO), a basic and necessary condition of remembering past experiences. The right prefrontal sites were near the frontal pole [Brodmann's area (BA) 10], frontal operculum (BA 47͞45), and lateral dorsal area (BA 8͞9). The two left prefrontal sites were homotopical with the right frontal pole and opercular sites. The same kinds of REMO sites were not observed in any other cerebral region. Many previous functional neuroimaging studies of episodic memory retrieval have reported activations near the frontal REMO sites identified here, although their function has not been clear. Many of these, too, probably have signaled their involvement in REMO. We propose that REMO activations largely if not entirely account for the frontal hemispheric asymmetry of retrieval as described by the original hemispheric encoding retrieval asymmetry model.

Right prefrontal cortex and episodic memory retrieval: a functional MRI test of the monitoring hypothesis (original) (raw)

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