Biomedical subjects

Daniel L Schacter

Publications and source records attributed to Daniel L Schacter.

15 recordsLinked to original sources

PubMed2003

Impaired hippocampal recruitment during normal modulation of memory performance in schizophrenia.

BACKGROUND: Patients with schizophrenia demonstrate poor verbal memory, ascribed to impaired prefrontal and hippocampal function. Healthy adults can increase recall accuracy following encoding interventions, such as item repetition and the formation of semantic associations. We examined the effects of these interventions on both memory performance and retrieval-related hippocampal activity in healthy adults and patients with schizophrenia. METHODS: Twelve patients with schizophrenia and twelve healthy control subjects participated. During study, subjects counted either the number of meanings or T-junctions in words seen only once or repeated four times. At test, O15-positron emission tomography scans were acquired while subjects completed word-stems with previously studied items. RESULTS: Control subjects recalled more words overall, but both groups demonstrated similar performance benefits following deeper encoding. Both item repetition and the use of a semantic encoding task were associated with memory retrieval-related hippocampal recruitment in control but not schizophrenic participants. Patients with schizophrenia demonstrated greater activation of prefrontal cortical areas during word retrieval. CONCLUSIONS: Despite a lack of hippocampal recruitment, patients with schizophrenia showed intact modulation of memory performance following both encoding interventions. Impaired hippocampal recruitment, in concert with greater prefrontal activation, may reflect a specific deficit in conscious recollection in schizophrenia.

Hippocampus↗

PubMed2003

Memory orientation and success: separable neurocognitive components underlying episodic recognition.

Episodic recognition can be based on recollection of contextual details, on a sense of recent encounter, or some combination of the two. According to several cognitive models, selectively attending to these distinct aspects of memory may require different retrieval orientations and result in different neural responses depending upon whether or not retrieval is successful. Using event-related fMRI, we examined retrieval orientation by having subjects discriminate between two test words in one of two manners. During source recollection, they selected the member of the pair previously associated with a particular encoding task. In contrast, recency judgment required selection of the most recently encountered item of the pair, regardless of how it had been encoded. Furthermore, successful and unsuccessful trials within each retrieval task were contrasted to determine whether retrieval success effects occurred in overlapping or dissimilar neural populations compared to those associated with each retrieval orientation. The results revealed distinct lateral prefrontal and parietal activations that distinguished attempted source recollection from judgments of relative recency; these orientation effects were largely independent of retrieval success. In contrast, medial temporal lobe structures (hippocampus and parahippocampal gyrus) were differentially more active during successful recollection of encoding context, showing similar reduced responses during failed source recollection and judgments of recency. These results indicate that different memory orientations recruit distinct prefrontal and parietal networks and that the recovery of episodic context is associated with the hippocampus and surrounding medial temporal cortices.

Adult↗

PubMed2003

Semantic versus phonological false recognition in aging and Alzheimer's disease.

Patients with Alzheimer's disease (AD) have been found to exhibit lower levels of false recognition of semantic associates compared with healthy older adults. Because these patients may show impaired performance of episodic and semantic memory tasks, this finding could be explained by deficits in episodic memory, semantic memory, or both. The authors adapted a paradigm for comparison of semantic versus phonological false recognition. They found that: (a) patients with AD exhibited lower levels of corrected false recognition of semantic, phonological, and hybrid (mixed semantic and phonological) lists than older adults, and (b) patients with AD showed very similar levels of false recognition for all list types. These results suggest that only episodic memory deficits are necessary to explain the lower level of false recognition of semantic associates observed in patients with AD when compared to older adults. Additionally, (c) older adults showed greater levels of semantic, phonological, and hybrid false recognition than younger adults, extending previous false recognition research of semantically related words and categorized colored photographs to phonologically related words.

Aged↗

PubMed2003

Feeling-of-knowing in episodic memory: an event-related fMRI study.

An individual may fail to recall an item from memory but still feel that it would be recognized on a later test, a retrieval state termed the "feeling-of-knowing" (FOK). In this study we used event-related fMRI and the FOK to examine both encoding- and retrieval-related factors that are associated with different levels of recall performance: successful retrieval of a previously studied item, retrieval failure accompanied by the FOK, and retrieval failure without any FOK. The results revealed one predominant pattern of retrieval-related activation: an intermediate level of activation for FOK-less than that associated with successful recall and greater than that associated with unsuccessful recall (frontal and left parietal cortices). Two further patterns were also observed: greater activation for both successful recall and FOK than for unsuccessful recall (left midlateral prefrontal cortex) and greater activation for successful recall than for both FOK and unsuccessful recall (left MTL). Analysis of encoding trials conditional upon subsequent retrieval success revealed a pattern of activation that appeared to predict subsequent recall, but which further analysis indicated to be a better predictor of subsequent recognition. These results provide evidence that the phenomenology of graded recall is represented neurally in frontal and parietal cortices, but that activation at encoding may not precipitate the different levels of recall experience.

Adolescent↗

PubMed2003

Neural mechanisms of visual object priming: evidence for perceptual and semantic distinctions in fusiform cortex.

Previous functional imaging studies have shown that facilitated processing of a visual object on repeated, relative to initial, presentation (i.e., repetition priming) is associated with reductions in neural activity in multiple regions, including fusiform/lateral occipital cortex. Moreover, activity reductions have been found, at diminished levels, when a different exemplar of an object is presented on repetition. In one previous study, the magnitude of diminished priming across exemplars was greater in the right relative to the left fusiform, suggesting greater exemplar specificity in the right. Another previous study, however, observed fusiform lateralization modulated by object viewpoint, but not object exemplar. The present fMRI study sought to determine whether the result of differential fusiform responses for perceptually different exemplars could be replicated. Furthermore, the role of the left fusiform cortex in object recognition was investigated via the inclusion of a lexical/semantic manipulation. Right fusiform cortex showed a significantly greater effect of exemplar change than left fusiform, replicating the previous result of exemplar-specific fusiform lateralization. Right fusiform and lateral occipital cortex were not differentially engaged by the lexical/semantic manipulation, suggesting that their role in visual object recognition is predominantly in the visual discrimination of specific objects. Activation in left fusiform cortex, but not left lateral occipital cortex, was modulated by both exemplar change and lexical/semantic manipulation, with further analysis suggesting a posterior-to-anterior progression between regions involved in processing visuoperceptual and lexical/semantic information about objects. The results are consistent with the view that the right fusiform plays a greater role in processing specific visual form information about objects, whereas the left fusiform is also involved in lexical/semantic processing.

Adolescent↗

PubMed2003

False recognition of abstract versus common objects in older and younger adults: testing the semantic categorization account.

Older adults often demonstrate higher levels of false recognition than do younger adults. However, in experiments using novel shapes without preexisting semantic representations, this age-related elevation in false recognition was found to be greatly attenuated. Two experiments tested a semantic categorization account of these findings, examining whether older adults show especially heightened false recognition if the stimuli have preexisting semantic representations, such that semantic category information attenuates or truncates the encoding or retrieval of item-specific perceptual information. In Experiment 1, ambiguous shapes were presented with or without disambiguating semantic labels. Older adults showed higher false recognition when labels were present but not when labels were never presented. In Experiment 2, older adults showed higher false recognition for concrete but not abstract objects. The semantic categorization account was supported.

Adolescent↗

PubMed2002

Executive control during episodic retrieval: multiple prefrontal processes subserve source memory.

During recognition, one may sense items as familiar (item memory) and additionally recollect specific contextual details of the earlier encounters (source memory). Cognitive theory suggests that, unlike item memory, source memory requires controlled cue specification and monitoring processes. Functional imaging suggests that such processes may depend on left prefrontal cortex (PFC). However, the nature and possible anatomical segregation of these processes remains unknown. Using functional magnetic resonance imaging, we isolated distinct response patterns in left PFC during source memory consistent with semantic analysis/cue specification (anterior ventrolateral), recollective monitoring (posterior dorsolateral and frontopolar), and phonological maintenance/rehearsal (posterior ventrolateral). Importantly, cue specification and recollective monitoring responses were not seen during item memory and were unaffected by retrieval success, demonstrating that the mere attempt to recollect episodic detail engages multiple control processes with different left PFC substrates.

Adolescent↗

PubMed2002

Retrieval of relational information: a role for the left inferior prefrontal cortex.

Neuroimaging studies have implicated different areas of prefrontal cortex and medial temporal lobe structures (MTL) in episodic retrieval tasks. However, the role of specific regions in particular aspects of episodic memory is still unclear. In this experiment we studied changes in regional cerebral blood flow (rCBF) associated with relational and nonrelational retrieval of studied pairs of words. For relational retrieval, a list of either studied or rearranged pairs was presented and subjects (n = 8) were asked to indicate whether pairs had appeared on the study list. Under the nonrelational retrieval condition they indicated whether one or both words of the pair had appeared on the study list. As compared to the baseline condition (looking at a cross-mark), increased rCBF was observed in the left inferior prefrontal cortex (LIPFC) for both studied pairs and rearranged pairs under the relational retrieval condition. Under the nonrelational condition, an increase was observed in right inferior frontal gyrus. The MTL showed a trend for increased rCBF in the rearranged-pair condition. This increase was probably associated with the encoding that accompanies retrieval of novel stimuli. Results suggest that the lateralized activation of prefrontal cortex observed in episodic memory tasks may be related to the degree of relational processing involved. The LIPFC appears to be associated with relational retrieval and the right prefrontal cortex with nonrelational retrieval.

Adolescent↗

PubMed2002

The effect of retrieval instructions on false recognition: exploring the nature of the gist memory impairment in amnesia.

In previous studies, we found that amnesic patients show reduced levels of false recognition in a converging semantic associates paradigm. This finding was interpreted as reflecting an impairment in amnesia in the ability to form, retain and/or retrieve a well-organized representation of the semantic 'gist' of studied items. To further explore the nature of amnesics' impairment in gist memory, the current study compared performance in two retrieval conditions. In a standard retrieval condition, participants were asked to endorse on a recognition test only items that had appeared on the study list. In a meaning retrieval condition, participants were asked to endorse any item that shared the meaning of studied items. Meaning retrieval instructions failed to eliminate the reduction in false recognition in amnesia. These results suggest that amnesics' impairment in gist memory is not attributable to a failure to access well-formed gist representations when given item-specific retrieval cues. Rather, it suggests that amnesic patients are impaired in their ability to encode, store, or maintain strong gist information.

Adult↗

PubMed2002

Memory distortion in people reporting abduction by aliens.

False memory creation was examined in people who reported having recovered memories of traumatic events that are unlikely to have occurred: abduction by space aliens. A variant of the Deese/Roediger-McDermott paradigm (J. Deese. 1959; H. L. Roediger III & K. B. McDermott, 1995) was used to examine false recall and false recognition in 3 groups: people reporting recovered memories of alien abduction. people who believe they were abducted by aliens but have no memories, and people who deny having been abducted by aliens. Those reporting recovered and repressed memories of alien abduction were more prone than control participants to exhibit false recall and recognition. The groups did not differ in correct recall or recognition. Hypnotic suggestibility, depressive symptoms, and schizotypic features were significant predictors of false recall and false recognition.

Adult↗

PubMed2002

Aging and strategic retrieval processes: reducing false memories with a distinctiveness heuristic.

The authors show that a strategic retrieval process--the distinctiveness heuristic--is a powerful mechanism for reducing false memories in the elderly. Individuals studied words, pictures, or both types of items and then completed a recognition test on which the studied items appeared once, whereas the new words appeared twice. After studying either pictures only or a mixture of pictures and words, both younger and older adults falsely recognized fewer repeated new words than did participants who studied words. Studying pictures provided a basis for using a distinctiveness heuristic during the recognition test: Individuals inferred that the absence of memory for picture information indicates that an item is "new."

Adolescent↗

PubMed2002

False recognition of pictures versus words in Alzheimer's disease: the distinctiveness heuristic.

False recognition of semantic associates can be reduced when older adults also study pictures representing each associate. D. L. Schacter, L. Israel, and C. Racine (1999) attributed this reduction to the operation of a distinctiveness heuristic: a response mode in which participants demand access to detailed recollections to support a positive recognition decision. The authors examined patients with probable Alzheimer's disease (AD) and older adults with this paradigm. Half of the participants studied pictures and auditory words; the other half studied visual and auditory words. Older adults who studied pictures were able to reduce their false alarms compared with those who studied words only. AD patients who studied pictures were unable to reduce their false alarms compared with those who studied words only and, in fact, exhibited trends toward greater false recognition. Implications for understanding semantic memory in AD patients are discussed.

Aged↗

PubMed2002

Hippocampal and brain stem activation during word retrieval after repeated and semantic encoding.

Repeated word presentation during learning and the use of a semantic encoding task both increase the accuracy of subsequent word retrieval. Previous neuroimaging studies have shown that successful word retrieval depends on the recruitment of the hippocampus, whereas the effort of retrieval is linked to activation of prefrontal cortex modules. We studied the effects of repetition (4x versus 1x presentation) and encoding task (semantic versus perceptual) on hippocampal and prefrontal cortex activation during word-stem cued recall using positron emission tomography. Repeated and semantic encoding resulted in increased recall accuracy, with word repetition showing a greater effect when using a semantic encoding task. The more successful retrieval of words presented repeatedly compared with words presented once was associated with activation of the left anterior hippocampus. The more successful retrieval of words encoded using a semantic compared with a perceptual task was associated with activation of the right posterior and, less significantly, the left anterior hippocampus. The greater benefit of repeated learning when using the semantic task was linked to activation of the right brainstem, in the region of the ventral tegmentum. Our results suggest that word repetition and semantic encoding increase recall accuracy during subsequent word retrieval via distinct hippocampal mechanisms and that ventral tegmentum activation is relevant for word retrieval after semantic encoding. These findings confirm the importance of hippocampal recruitment during word retrieval and provide novel evidence for a role of brainstem neurons in word retrieval after semantic encoding.

Adult↗

PubMed2002

Intact suppression of increased false recognition in schizophrenia.

OBJECTIVE: Recognition memory is impaired in patients with schizophrenia, as they rely largely on item familiarity, rather than conscious recollection, to make mnemonic decisions. False recognition of novel items (foils) is increased in schizophrenia and may relate to this deficit in conscious recollection. By studying pictures of the target word during encoding, healthy adults can suppress false recognition. This study examined the effect of pictorial encoding on subsequent recognition of repeated foils in patients with schizophrenia. METHOD: The study included 40 patients with schizophrenia and 32 healthy comparison subjects. After incidental encoding of 60 words or pictures, subjects were tested for recognition of target items intermixed with 60 new foils. These new foils were subsequently repeated following either a two- or 24-word delay. Subjects were instructed to label these repeated foils as new and not to mistake them for old target words. RESULTS: Schizophrenic patients showed greater overall false recognition of repeated foils. The rate of false recognition of repeated foils was lower after picture encoding than after word encoding. Despite higher levels of false recognition of repeated new items, patients and comparison subjects demonstrated a similar degree of false recognition suppression after picture, as compared to word, encoding. CONCLUSIONS: Patients with schizophrenia displayed greater false recognition of repeated foils than comparison subjects, suggesting both a decrement of item- (or source-) specific recollection and a consequent reliance on familiarity in schizophrenia. Despite these deficits, presenting pictorial information at encoding allowed schizophrenic subjects to suppress false recognition to a similar degree as the comparison group, implying the intact use of a high-level cognitive strategy in this population.

Adult↗

PubMedDate not supplied

Use of a false recognition paradigm in an Alzheimer's disease clinical trial: a pilot study.

We report the first use of a false recognition memory test in a clinical trial of patients with Alzheimer's disease (AD). Tests of false recognition allow measurement of two components of memory: the specific details of a prior encounter with a particular item (item-specific recollection) and the general meaning, idea, or gist conveyed by a collection of items (gist memory). We used a false recognition paradigm with categorized pictures to study the effects of an experimental medication in patients with AD. Because medications to treat AD may preferentially improve gist memory or item-specific recollection, use of this type of paradigm may improve sensitivity for detection of drug effects more than standard memory tests.

Aged↗