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PubMed2006

Anatomical and functional alterations in semantic dementia: a voxel-based MRI and PET study.

Rare studies have used magnetic resonance imaging (MRI) and voxel-based morphometry (VBM) to assess atrophy, and only two positron emission tomography (PET) studies used SPM to examine functional changes in semantic dementia (SD). Our aim was to highlight both morphological and functional abnormalities in a same group of 10 SD patients, in the entire brain, using a "state of the art" methodology (optimized VBM procedure, PET data corrected for partial volume effects and voxel-based analyses). We also used an extensive neuropsychological battery. We showed that main alterations concerned the left temporal lobe, in accordance with the striking impairment of semantic memory in SD patients, as well as the hippocampal region, which may partly explain their moderate episodic memory deficits. Hypometabolism was more extensive than grey matter loss in both temporal lobes, and specifically concerned the orbitofrontal areas, consistent with the moderate impairment of executive functions and behavioural changes. While PET is more sensitive than MRI, there is striking concordance between morphological and functional abnormalities, which contrasts with the discordance observed in Alzheimer's disease and might be a typical feature of SD.

Adaptation, Physiological↗

PubMed1997

General lexical slowing and the semantic priming effect: the roles of age and ability.

Older adults performed three lexical information-processing tasks approximately 1.3 times slower than young adults. Consistent with general lexical slowing, slopes of regressions based on individual subjects' RTs on two of the tasks (single lexical decision and category judgment) did not differ from slopes based on the third (double lexical decision) task. Moreover, slopes based on the single lexical decision and category judgment tasks accurately predicted the size of semantic priming effects on the third (double lexical decision) task. This was true for the older group as a whole, and also for subgroups of fast, medium and slow older adults, as well as for young adult subgroups. The size of the semantic priming effects for the fast old and slow young subgroups (who differed in age but not in processing speed) were approximately equal, consistent with the idea that the effect of age on priming is entirely attributable to slowing. Across all tasks, each old subgroup (fast, medium, or slow) showed the same degree of slowing relative to the corresponding young subgroup, so that the differences in RTs observed between subgroups in the young sample were magnified in the old sample. Taken together, the present findings suggest that ability-related differences in lexical processing speed may be functionally equivalent to age-related differences and that both factors interact to determine performance on speeded lexical tasks.

Adult↗

PubMed2002

Preserved calculation skills in a case of semantic dementia.

We present the case of a patient, BET, with a profound semantic dementia who shows a selective preservation of many aspects of number knowledge. In the context of an otherwise global loss of visual and verbal semantic knowledge, our patient demonstrates relatively intact number processing and numerical calculation in both the verbal and visual domain. More remarkably, BET is able to harness her intact calculation skills to number problem solving tasks. Our report provides further evidence that high-level non-verbal reasoning may persist in the absence of any viable language skills.

Aged↗

PubMed1997

Lexical and semantic processing in the absence of word reading: evidence from neglect dyslexia.

Nine patients with left-sided neglect and nine matched control patients performed three tasks on horizontal (either normal or mirror-reversed) letter strings. The tasks were: reading aloud, making a lexical decision (word vs non-word), and making a semantic decision (living vs non-living item). Relative to controls, neglect patients performed very poorly in the reading task, whereas they performed nearly normally in the lexical and semantic tasks. This was considered to be a dissociation between direct tasks, rather than a dissociation between explicit and implicit knowledge. The explanation offered for the dissociation is in terms of both a dual-route model for reading aloud and a degraded representation of the letter string.

Aged↗

PubMed2000

The nature and staging of attention dysfunction in early (minimal and mild) Alzheimer's disease: relationship to episodic and semantic memory impairment.

The development of cholinergic therapies for Alzheimer's disease (AD) has highlighted the importance of understanding the role of attentional deficits and the relationship between attention and memory in the earliest stages of the disease. Variability in the tasks used to examine aspects of attention, and in the disease severity, between studies makes it difficult to determine which aspects of attention are affected earliest in AD, and how attentional impairment is related to other cognitive modules. We tested 27 patients in the early stages of the disease on the basis of the MMSE (minimal 24-30 corresponding to minimal cognitive impairment, very mild or possible AD in other classifications; and mild 18-23) on a battery of attentional tests aimed to assess sustained, divided, and selective attention, plus tests of episodic memory, semantic memory, visuoperceptual and visuospatial function, and verbal short-term memory. Although the mildly demented group were impaired on all attentional tests, the minimally impaired group showed a preserved ability to sustain attention, and to divide attention based on a dual-task paradigm. The minimally demented group had particular problems with response inhibition and speed of attentional switching. Examination of the relationship between attention and other cognitive domains showed impaired episodic memory in all patients. Deficits in attention were more prevalent than deficits in semantic memory suggesting that they occur at an earlier stage and the two were partially independent. Impairment in visuoperceptual and visuospatial functions and verbal short-term memory were the least common. Although attention is impaired early in AD, 40% of our patients showed deficits in episodic memory alone, confirming that amnesia may be the only cognitive deficit in the earliest stages of sporadic AD.

Aged↗

PubMed2001

Exploring the neural bases of episodic and semantic memory: the role of structural and functional neuroimaging.

Exploration of the neural bases of episodic and semantic memory is best pursued through the combined examination of the effects of identified lesions on memory and functional neuroimaging of both normal people and patients when they engage in memory processing of various kinds. Both structural and functional neuroimaging acquisition and analysis techniques have developed rapidly and will continue to do so. This review briefly outlines the history of neuroimaging as it impacts on memory research. Next, what has been learned so far from lesion-based research is outlined with emphasis on areas of disagreement as well as agreement. What has been learned from functional neuroimaging, particularly emission tomography and functional magnetic resonance imaging, is then discussed, and some stress is placed on topics where the interpretation of imaging studies has so far been unclear. Finally, how functional and structural imaging techniques can be optimally used to help resolve three areas of disagreement in the lesion literature will be discussed. These disagreements concern what the hippocampus and perirhinal cortex contribute to memory; whether any form of priming depends on the medial temporal lobes; and whether remote episodic as well as semantic memories cease to depend on the medial temporal lobes. Although the discussion will show the value of imaging techniques, it will also emphasize some of the limitations of current neuroimaging studies.

Brain↗

PubMed2003

Are poor readers semantically challenged? An event-related brain potential assessment.

This study explores visual event-related potentials components in a group of poor readers (PRs) and control children who carried out figure and word categorization tasks. In both tasks, every child had to categorize between animal and non-animal stimuli in an odd-ball GO-GO paradigm. During the word categorization task, PRs presented longer reaction times, a poorer performance, longer and larger P2 amplitudes, and smaller amplitudes and longer P300 latencies than controls. There were no differences in the N400 component between groups. These results suggest that semantic processing underachievement in PRs may not be a semantic deficit per se, but the late reflection of an early word codification problem, deficient use of attentional resources and lack of target identification during reading.

Analysis of Variance↗

PubMed2001

Electrophysiological estimates of semantic and syntactic information access during tacit picture naming and listening to words.

We investigated the relative time courses of the accessibility of semantic and syntactic information in speaking and comprehension via event-related brain potentials (ERPs). Native German speakers either viewed a series of pictures (tacit picture naming experiment) or heard a series of nouns (listening experiment) and made dual choice go/nogo decisions based on each item's semantic and syntactic features. N200 peak latency results indicate that access to meaning has temporal precedence over access to syntactic information in both speaking (approximately 80 ms) and comprehension (approximately 70 ms), and are discussed in the context of current psycholinguistic theories.

Adult↗

PubMed1998

Auditory event-related potentials to semantic priming during sleep.

The present study uses the N400 component of event-related potentials (ERPs) as a processing marker of single spoken words presented during sleep. Thirteen healthy volunteers participated in the study. The auditory ERPs were registered in response to a semantic priming paradigm made up of pairs of words (50% related, 50% unrelated) presented in the waking state and during sleep stages II, III-IV and REM. The amplitude, latency and scalp distribution parameters of the negativity observed during stage II and the REM stage were contrasted with the results obtained in the waking state. The 'N400-like' effect elicited in these stages of sleep showed a mean amplitude for pairs of unrelated words significantly greater than for related pairs and an increment of latency. These results suggest that during these sleep stages a semantic priming effect is maintained actively although the lexical processing time increases.

Adult↗

PubMed2003

The influence of semantic priming on event-related potentials to painful laser-heat stimuli in migraine patients.

We investigated the effects of different semantic primes on the processing of painful stimuli in migraine patients. For prime stimuli, descriptors of three categories were used: somatosensory pain-related, affective pain-related, and neutral adjectives. While migraine patients (n = 17) processed these primes, a painful laser-heat stimulus was applied to the dorsum of the left hand. Laser-evoked potentials (LEPs) were recorded and pain intensity ratings were obtained after each single laser stimulus. Pain thresholds were significantly lower in patients than in control subjects. LEP amplitudes were also significantly smaller in patients than in controls, but this effect could be explained by differences in applied stimulus intensity. Within the group of migraine patients, LEP amplitudes at 300 ms post laser stimulus and N2-P2 peak-to-peak amplitudes were significantly enlarged when applied while subjects processed pain-related as compared to non-pain-related primes, i.e. patients showed a pattern of priming effect similar to that of the control group. Additionally, patients recognised more affective words than control subjects, and affective pain-related primes tended to enhance the P2 amplitude of LEP more than somatosensory pain-related primes. It is suggested that pain-related semantic primes might pre-activate neural networks subserving pain memory and pain processing.

Adult↗

PubMed2002

Relating semantic and episodic memory systems.

Episodic and semantic memory are two forms of declarative memory which appear to function in distinct yet interdependent ways. Here we provide direct evidence for a functional relationship between these two memory systems by showing that left lateral temporal lobe regions involved in semantic memory play an important role in accurate episodic memory retrieval.

Adolescent↗

PubMed2002

The impact of semantic memory organization and sentence context information on spoken language processing by younger and older adults: an ERP study.

To examine changes in semantic memory organization and use during aging, we recorded event-related potentials as younger and older adults listened to sentences ending with the expected word, an unexpected word from the same semantic category, or an unexpected word from a different category. Half of the contexts were highly constraining. In both groups, expected words elicited less negativity 300-500 ms (N400) than unexpected ones, and unexpected words elicited smaller N400s when these were categorically related. Whereas younger adults showed the greatest N400 reduction to unexpected but related words in high constraint contexts, older adults showed the opposite tendency. Thus, unlike younger adults, older adults as a group do not seem to be using context predictively. Older adults with higher verbal fluency and larger vocabularies, however, showed the younger response pattern, suggesting resource availability may offset certain age-related changes.

Adolescent↗

PubMed2005

Constructivism, the so-called semantic learning theories, and situated cognition versus the psychological learning theories.

In this paper, the perspective of situated cognition, which gave rise both to the pragmatic theories and the so-called semantic theories of learning and has probably become the most representative standpoint of constructivism, is examined. We consider the claim of situated cognition to provide alternative explanations of the learning phenomenon to those of psychology and, especially, to those of the symbolic perspective, currently predominant in cognitive psychology. The level of analysis of situated cognition (i.e., global interactive systems) is considered an inappropriate approach to the problem of learning. From our analysis, it is concluded that the pragmatic theories and the so-called semantic theories of learning which originated in situated cognition can hardly be considered alternatives to the psychological learning theories, and they are unlikely to add anything of interest to the learning theory or to contribute to the improvement of our knowledge about the learning phenomenon.

Cognition↗

PubMed2001

Differential episodic and semantic memory performance in Alzheimer's disease and vascular dementias.

Differential performance on measures of episodic and semantic memory were examined in AD, cortical vascular dementia (CVaD), subcortica] vascular dementia (SVaD), and controls. Groups were matched on age, education, and gender; dementia groups also were matched on severity. Recognition/retrieval differences were found only between SVaD and AD groups, not between CVaD and AD. Thus, recognition/retrieval differences are likely secondary to subcortical pathology rather than to vascular etiology per se. Similarly, significant numbers of memory errors were associated with cortical pathology, regardless of etiology. Error rate differences were found only between SVaD and AD groups, not between CVaD and AD. Finally, rapid forgetting was unique to AD; however, since no difference was found between SVaD and AD, rapid forgetting may occur only as AD progresses. No semantic memory measure differentiated AD from either CVaD or SVaD subjects. Results suggest that some previously reported episodic differences may be due to cortical versus white matter subcortical pathology, rather than to AD versus vascular etiology.

Aged↗

PubMedDate not supplied

SemanticEye: a semantic web application to rationalize and enhance chemical electronic publishing.

SemanticEye, an ontology with associated tools, improves the classification and open accessibility of chemical information in electronic publishing. In a manner analogous to digital music management, RDF metadata encoded as Adobe XMP can be extracted from a variety of document formats, such as PDF, and managed in an RDF repository called Sesame. Users upload electronic documents containing XMP to a central server by "dropping" them into WebDAV folders. The documents can then be navigated in a Web browser via their metadata, and multiple documents containing identical metadata can then be aggregated. SemanticEye does not actually store any documents. By including unique identifiers within the XMP, such as the DOI, associated documents can be retrieved from the Web with the help of resolving agents. The power of this metadata driven approach is illustrated by including, within the XMP, InChI identifiers for molecular structures and finding relationships between articles based on their InChIs. SemanticEye will become increasingly more comprehensive as usage becomes more widespread. Furthermore, following the Semantic Web architecture enables the reuse of open software tools, provides a "semantically intuitive" alternative to search engines, and fosters a greater sense of trust in Web-based scientific information.

Journal Article↗

PubMed2000

Isomer generation: semantic rules for detection of isomorphism

The problem of exhaustive generation of a nonredundant set of structural formulas (graphs) of acyclic alkanes was considered. A technique based on the compressed adjacency matrix (CAM) was proposed. The algorithm generates CAMs, which encode trees numbered according to the Morgan naming algorithm. Out of this set of CAMs those corresponding to the maximal Morgan codes--which in fact are the CAMs of canonically numbered isomers--must be found. CAMs are conceived as "sentences" of a primitive language. Sentences violating the syntactic and semantic rules of this language have to be discarded. In this paper three semantic rules have been proposed. The algorithm devised is efficient, and the decision to retain or to reject the actual structure does not involve any comparison with other structures. It was proved that several subsets of CAMs will not contain any maximal CAM and therefore it is not necessary to generate them. The whole procedure was illustrated by generating CAMs of all acyclic graphs containing nine vertices.

Journal Article↗

PubMed1997

Comparing the difficulty of letter, semantic, and name fluency tasks for normal elderly and patients with Parkinson's disease.

Research on the effect of Parkinson's disease (PD) on verbal fluency has produced conflicting results. In this study, 88 PD patients with no dementia, 11 PD patients with questionable mental status, 15 PD patients with dementia, and 46 elders free from mental disorder were administered a variety of semantic, letter, and name fluency tasks. The results revealed that, contrary to popular assumption, semantic fluency was not always superior to letter fluency. Rather, verbal fluency was influenced by the nature of the individual categories. Interestingly, the relative difficulty of many categories was fairly stable across groups. The results also indicated that the individual fluency tasks were differentially sensitive to the mental status of the PD patients. Overall, the findings suggest that closer attention to the nature of the tested categories may help clarify the inconsistent effects of PD on verbal fluency.

Aged↗

PubMed1997

Automatic versus controlled semantic priming in schizophrenia.

Schizophrenic individuals (n = 31), including paranoid and nonparanoid diagnostic subgroups, and normal controls (n = 20) participated in a semantic priming experiment involving a single-choice lexical decision task. For the automatic priming blocks, a 260-ms stimulus onset asynchrony (SOA) was used; for the controlled priming blocks, 1,000-ms SOA was used. The paranoid subgroup showed significantly less priming than did the control group. The nonparanoid subgroup showed a decrease in priming compared with the control group that approached significance. There was an increased priming effect for the controlled compared with the automatic priming condition; this difference was not modulated by participant group. Nonsignificant semantic priming (equal to 0) occurred only for schizophrenic subgroups and only in automatic priming conditions.

Adult↗