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ABSTRACT: fMRI responses to recognition memory test items in two regions of ventral lateral parietal cortex-the angular gyrus and temporo-parietal junction (TPJ)-are enhanced when recognition is accompanied by recollection. According to the 'episodic buffer' hypothesis, ventral parietal recollection effects reflect processes involved in maintaining or representing recollected information. According to the 'attention to memory' hypothesis, however, the effects reflect attentional re-orienting to the products of recollection. The present experiment addressed the question whether these operations map on to the angular gyrus and TPJ, respectively. Subjects were scanned during a memory test that required a Remember/Know/New and a source memory judgment, allowing recollected items to be segregated by amount of contextual information recollected. Angular gyrus activity tracked amount of recollected information, whereas activity in the TPJ was enhanced for items endorsed as recollected, but was insensitive to amount of information recollected. Thus, the two regions likely support functionally dissociable processes.
Cognitive neuroscience 09/2012; 3(3-4):142-149. · 0.77 Impact Factor
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ABSTRACT: Dual-process models of recognition memory distinguish between the retrieval of qualitative information about a prior event (recollection), and judgments of prior occurrence based on an acontextual sense of familiarity. fMRI studies investigating the neural correlates of memory encoding and retrieval conducted within the dual-process framework have frequently reported findings consistent with the view that the hippocampus selectively supports recollection, and has little or no role in familiarity-based recognition. An alternative interpretation of these findings has been proposed, however, in which it is argued that the hippocampus supports the encoding and retrieval of 'strong' memories, regardless of whether the memories are recollection- or familiarity-based. Here, we describe the findings of eight fMRI studies from our laboratory: one study of source memory encoding, four studies of the retrieval of contextual information, and three studies of continuous recognition. Together, the findings support the proposal that hippocampal activity co-varies with the amount of contextual information about a study episode that is encoded or retrieved, and not with the strength of an undifferentiated memory signal.
Neuropsychologia 06/2012; · 3.64 Impact Factor
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ABSTRACT: It has been proposed that the hippocampus selectively supports retrieval of contextual associations, but an alternative view holds that the hippocampus supports strong memories regardless of whether they contain contextual information. We employed a memory test that combined the 'Remember/Know' and source memory procedures, which allowed test items to be segregated both by memory strength (recognition accuracy) and, separately, by the quality of the contextual information that could be retrieved (indexed by the accuracy/confidence of a source memory judgment). As measured by fMRI, retrieval-related hippocampal activity tracked the quality of retrieved contextual information and not memory strength. These findings are consistent with the proposal that the hippocampus supports contextual recollection rather than recognition memory more generally.
Hippocampus 11/2011; 22(6):1429-37. · 5.18 Impact Factor
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ABSTRACT: fMRI (1.5 mm isotropic voxels) was employed to investigate the relationship between hippocampal activity and memory strength in a continuous recognition task. While being scanned, subjects were presented with colored photographs that each appeared on four occasions. The requirements were to make one response when an item was presented for the first or the third time and to make a different response when an item appeared for the second or the fourth time. Consistent with prior findings, items presented for the first time elicited greater hippocampal and parahippocampal activity than repeated items. The activity elicited by repeated items declined linearly as a function of number of presentations ("graded" new > old effects). No medial-temporal lobe regions could be identified where activity elicited by repeated items exceeded that for new items or where activity elicited by repeated items increased with number of presentations. These findings are inconsistent with the proposal that retrieval-related hippocampal activity is positively correlated with memory strength. We also identified graded new > old effects in several cortical regions outside the medial-temporal lobe, including the left retrosplenial/posterior cingulate cortex and the right lateral occipito-temporal cortex. By contrast, graded old > new effects were evident in bilateral mid-intraparietal sulcus and precuneus.
Journal of Cognitive Neuroscience 06/2011; 23(6):1522-32. · 5.18 Impact Factor
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ABSTRACT: We used high-resolution functional magnetic resonance imaging to investigate whether successful recollection during continuous recognition is associated with relative enhancement of hippocampal activity, consistent with prior findings from experiments employing separate study and test phases. While being scanned, subjects discriminated between new and repeated pictures. Each picture, which was repeated once after an interval of between 10 and 30 items, was surrounded by a frame that was colored gray, blue, or orange. When an item repeated, its frame color determined the correct response. Repeated items surrounded by a gray frame always required an "old" judgment. A repeated item surrounded by a blue or an orange frame required a different response depending whether it was represented in the same (Target) or a different (Nontarget) color from the first presentation. Consistent with the results from previous continuous recognition experiments, robust new > old effects were found in bilateral hippocampus. In addition, an across-subjects correlational analysis identified a cluster of voxels in right hippocampus where recollection-related activity (operationalized by the contrast between correctly vs. incorrectly judged Nontargets) was positively correlated with recollection performance. Thus, successful recollection during continuous recognition is associated with a relative enhancement of hippocampal activity.
Hippocampus 03/2010; 21(6):575-83. · 5.18 Impact Factor
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ABSTRACT: Episodic memory retrieval is thought to involve reinstatement of the neurocognitive processes engaged when an episode was encoded. Prior fMRI studies and computational models have suggested that reinstatement is limited to instances in which specific episodic details are recollected. We used multivoxel pattern-classification analyses of fMRI data to investigate how reinstatement is associated with different memory judgments, particularly those accompanied by recollection versus a feeling of familiarity (when recollection is absent). Classifiers were trained to distinguish between brain activity patterns associated with different encoding tasks and were subsequently applied to recognition-related fMRI data to determine the degree to which patterns were reinstated. Reinstatement was evident during both recollection- and familiarity-based judgments, providing clear evidence that reinstatement is not sufficient for eliciting a recollective experience. The findings are interpreted as support for a continuous, recollection-related neural signal that has been central to recent debate over the nature of recognition memory processes.
Neuron 09/2009; 63(5):697-708. · 14.74 Impact Factor
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ABSTRACT: Prior studies indicate that, in tests of recognition memory, ERPs elicited by correctly recognized test items differ according to whether the items were encoded in an emotionally arousing or an emotionally neutral study context. These prior studies employed only a relatively brief (ca. 10 min) retention interval, however. The present study contrasted the ERP correlates of incidental emotional retrieval as a function of study-test delay. Pictures of emotionally neutral objects were encoded in association with either emotionally negative or emotionally neutral scenes. In a repeated measures design (N=19), half of the objects were subjected to a recognition memory test 10 min after completion of the study phase, whereas the remainder were tested 24 h later. After the short delay, ERPs elicited by objects paired with emotional vs. neutral backgrounds differed from around 200 ms post-stimulus, the objects paired with the emotional scenes eliciting the more positive-going waveforms. After 24 h, differences between the ERPs elicited by the two classes of object were still apparent from around 200 ms post-stimulus. Strikingly, these effects differed from those obtained 10 min after study in both their polarity and scalp distribution. The early onset of these ERP effects suggests that they may reflect a form of memory independent of the conscious recollection of the associated study contexts. The qualitative differences in the effects at the two retention intervals raise the possibility that the encoded objects were subjected to consolidation processes that differed according to the emotional attributes of their study contexts.
Brain research 04/2009; 1269:105-13. · 2.46 Impact Factor
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ABSTRACT: We used a continuous recognition procedure that included multiple presentations of test items, along with high-resolution functional magnetic resonance imaging (fMRI), to investigate the relationship between item novelty and recognition-related activity in the medial temporal lobe (MTL). In several regions of hippocampus and parahippocampal cortex, activity elicited by new items exceeded that for old items, whereas no MTL regions exhibited greater activity for old items. Critically, anatomically distinct regions of MTL were engaged by item novelty in two different ways, as evidenced by statistically dissociable profiles of activity. In bilateral medial hippocampus and left posterior parahippocampal cortex, activity followed a categorical profile in which it was greater for new than old items but did not differ further with additional presentations of old items. By contrast, effects in adjacent regions of right lateral hippocampus and left parahippocampal cortex were graded, whereby activity declined linearly with respect to each successive item presentation. These findings suggest that the relationship between hippocampal (and parahippocampal) activity and continuous psychological dimensions, such as item novelty, cannot be captured by a unitary function.
Hippocampus 07/2008; 18(10):975-80. · 5.18 Impact Factor
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ABSTRACT: Post-retrieval processes are thought to be engaged when the outcome of an attempt to retrieve information from long-term memory must be monitored or evaluated. Previous research employing event-related potentials (ERPs) has implicated a specific ERP modulation - the 'right frontal old/new effect' - as a correlate of post-retrieval processing. In two experiments we examined whether the right frontal effect is specifically associated with processing of the products of an episodic retrieval attempt. During study, subjects in both experiments made one of two semantic judgments on serially presented pictures. In experiment 1, one study phase was followed by a source memory task, in which subjects responded 'new' to unstudied pictures and signaled the semantic judgment made on each studied picture. A separate study phase was followed by a task in which the studied items required a judgment about their semantic attributes. Robust right frontal effects were elicited by old items in both tasks, indicating that the effects are not selective for the monitoring of the content of information retrieved from episodic memory. In experiment 2, separate study phases were followed by test phases where semantic judgments were made either on old items (as in experiment 1), or on new items. Right frontal effects were elicited by whichever class of items, old or new, required the semantic judgment. Together, these findings indicate that the right frontal old/new effect reflects generic monitoring or decisional processes, rather than processing dedicated to the evaluation of the products of an episodic retrieval attempt.
Neuropsychologia 05/2008; 46(5):1211-23. · 3.64 Impact Factor
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ABSTRACT: The neural correlates of episodic retrieval ('recollection') have been shown to differ according to the content of retrieved episodes. It has been hypothesized that these content-dependent differences reflect the 'reinstatement' of encoding-related processes or representations at the time of recollection. It remains unclear, however, whether these effects directly reflect the recollection of differential episodic content, as would be predicted by the reinstatement hypothesis, or whether they are instead associated with processes that are contingent on successful recollection. To address this issue, the present study employed event-related potentials (ERPs), permitting the investigation of the temporal dynamics of content-dependent neural effects during retrieval, and in particular, their onset with respect to well-established ERP correlates of recollection, such as the left parietal old-new effect. Subjects studied a series of words that were each presented in the context of one of two encoding tasks. One task required the covert generation of a sentence incorporating each word, whereas the other required imagining the object corresponding to each word within a superimposed scenic picture. Memory for the words was subsequently tested with the 'remember/know' procedure. ERPs elicited by recollected words differed according to the prior encoding history of the word, beginning at approximately 300 ms following word onset. These content-dependent ERP differences were maximal over the anterior scalp and, importantly, onset as early as the left parietal old-new effect. The findings demonstrate that content-dependent neural activity during retrieval can occur in a timeframe that is compatible with a direct role in the recollection and representation of episodic information.
NeuroImage 02/2008; 39(1):406-16. · 5.89 Impact Factor
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ABSTRACT: The principle of transfer-appropriate processing and the cortical reinstatement hypothesis are two influential theoretical frameworks, articulated at the psychological and neurobiological levels of explanation, respectively, that each propose that the processes supporting the encoding and retrieval of episodic information are strongly interdependent. Here, we integrate these two frameworks into a single model that generates predictions that can be tested using functional neuroimaging methods in healthy humans, and then go on to describe findings that are in accord with these predictions. Consistent with the transfer-appropriate processing and cortical reinstatement frameworks, the neural correlates of successful encoding vary according to how retrieval is cued, and the neural correlates of retrieval are modulated by how items are encoded. Thus, encoding and retrieval should not be viewed as separate stages of memory that can be investigated in isolation from one another.
Progress in brain research 02/2008; 169:339-52. · 3.04 Impact Factor
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ABSTRACT: The neural correlates of episodic memory retrieval ("recollection") differ according to the type of information contained in the recollected episode. Such content-specific recollection effects have been hypothesized to reflect the reinstatement of processes or representations active during encoding. Using event-related functional magnetic resonance imaging, we evaluated this hypothesis by directly contrasting the neural activity elicited during the encoding and subsequent recollection of words studied with one of 2 encoding tasks. Study words appearing on pictures of scenes required imagining the word's referent at any location within the scene, whereas words appearing on a blank background required generating a sentence that incorporated the word. On a later memory test, the neural correlates of recollection were operationalized by contrasting the activity elicited during correct "remember" versus "know" responses. Recollected words from the "scene" task elicited activity in regions of left occipital cortex and anterior fusiform gyrus that overlapped regions where encoding-related activity was greater for the scene than sentence task. Conversely, activity elicited by words recollected from the "sentence" task overlapped with a region of ventromedial frontal cortex where encoding-related activity was greater for the sentence task. These content-specific associations between encoding- and recollection-related neural activity strongly support the reinstatement hypothesis of episodic retrieval.
Cerebral Cortex 12/2007; 17(11):2507-15. · 6.54 Impact Factor
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ABSTRACT: Studies employing event-related potentials (ERPs) during tests of recognition memory have reported differences in neural activity elicited by new test items according to the specific demands of the retrieval task, such as retrieving studied words versus pictures. The present study investigated whether differential processing of new items is possible when retrieval demands vary unpredictably on a trial-by-trial basis. In separate study-test phases, subjects encoded lists of intermixed words and pictures, and undertook retrieval tests with words as test items. Each test item was preceded by a task cue that signaled whether subjects were to attempt to retrieve a word or a picture from the study list. In the "blocked"condition, the targeted study material remained constant throughout the test, whereas in the "mixed"condition, the targeted material varied unpredictably across trials. New-item ERPs were more positive-going when words rather than pictures were targeted in the "blocked" condition, replicating previous findings, but this effect was absent in the "mixed"condition. The findings are consistent with the hypothesis that differential processing of retrieval cues depends upon the adoption of different task sets ("retrieval orientations" that develop over multiple trials and cannot be adjusted merely in response to an instructional cue. Unlike the new-item ERPs, ERPs elicited by the task cues in the mixed condition differed according to targeted material, but only on trials when there was a switch between target material. The implications of these findings for understanding the different retrieval strategies engaged when retrieval demands are consistent versus inconsistent are discussed.
Journal of Cognitive Neuroscience 10/2006; 18(9):1531-44. · 5.18 Impact Factor
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ABSTRACT: Retrieval orientation refers to the differential processing of retrieval cues according to the type of information sought from memory (e.g., words vs. pictures). In the present study, event-related potentials (ERPs) were employed to investigate whether the neural correlates of differential retrieval orientations are sensitive to the specificity of the retrieval demands of the test task. In separate study-test phases, subjects encoded lists of intermixed words and pictures, and then undertook one of two retrieval tests, in both of which the retrieval cues were exclusively words. In the recognition test, subjects performed 'old/new' discriminations on the test items, and old items corresponded to only one class of studied material (words or pictures). In the exclusion test, old items corresponded to both classes of study material, and subjects were required to respond 'old' only to test items corresponding to a designated class of material. Thus, demands for retrieval specificity were greater in the exclusion test than during recognition. ERPs elicited by correctly classified new items in the two types of test were contrasted according to whether words or pictures were the sought-for material. Material-dependent ERP effects were evident in both tests, but the effects onset earlier and offset later in the exclusion test. The findings suggest that differential processing of retrieval cues, and hence the adoption of differential retrieval orientations, varies according to the specificity of the retrieval goal.
Brain Research 03/2006; 1071(1):153-64. · 2.73 Impact Factor
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ABSTRACT: It is widely assumed that episodic retrieval (recollection) involves reinstatement of cortical activity engaged during the processing of an episode when it was initially experienced. It follows from this assumption that the cortical correlates of recollection should differ with the content of what is recollected, and that retrieval of different content should be associated with activity in functionally distinct cortical regions. The present experiment investigated these predictions. Subjects (N=17) studied a mixed list of words and pictures and were then presented with a test list comprised of words only. Test items were studied words, the names of studied pictures, and unstudied (new) words. Functional magnetic resonance images were acquired while the subjects made Remember/Know/New judgments to these test words. Independent of study material, studied items endorsed as Remembered elicited greater activity than correctly classified unstudied items in several regions, including left frontal, left lateral parietal, and posterior cingulate cortex. In addition, Remembered items elicited greater activity in the right hippocampus and parahippocampal gyrus than items accorded Know judgments, replicating previous findings. Analysis of content-specific effects demonstrated a regional double-dissociation within left fusiform cortex; recollected words elicited greater activity than recollected pictures in lateral fusiform, whereas the reverse effect was evident in an anterior fusiform region. The lateral and anterior fusiform areas correspond closely to areas held to be functionally specialized for the processing of visual words and pictures, respectively. Thus, the current findings support the cortical reinstatement hypothesis of episodic retrieval.
Neuropsychologia 02/2005; 43(7):1022-32. · 3.64 Impact Factor
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ABSTRACT: The principle of transfer-appropriate processing and the cortical reinstatement hypothesis are two influential theoretical frameworks, articulated at the psychological and neurobiological levels of explanation, respectively, that each propose that the processes supporting the encoding and retrieval of episodic information are strongly interdependent. Here, we integrate these two frameworks into a single model that generates predictions that can be tested using functional neuroimaging methods in healthy humans, and then go on to describe findings that are in accord with these predictions. Consistent with the transfer-appropriate processing and cortical reinstatement frameworks, the neural correlates of successful encoding vary according to how retrieval is cued, and the neural correlates of retrieval are modulated by how items are encoded. Thus, encoding and retrieval should not be viewed as separate stages of memory that can be investigated in isolation from one another.
Progress in Brain Research.
