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PubMed2005

Functional disconnection of the semantic networks in schizophrenia.

Patients with schizophrenia exhibit deficits in semantic processing, which can form the basis of thought disorders. The objective of this study was to explore functional connectivity between the activated areas during semantic processing in schizophrenia. Twelve patients with schizophrenia and 12 healthy controls were studied with [15O]H2O positron-emission tomography during semantic judgment. The expected activation in the left inferior occipitotemporal cortex significantly correlated with several other regional activations in normal study participants, but with no other regional activations in patients with schizophrenia. This finding suggests that schizophrenia involves a disconnection of semantic networks. The resultant distortion in semantic processing may have an impact on thought disorders.

Adult↗

PubMedDate not supplied

Semantic dementia and primary progressive aphasia: a problem of categorization?

The relationship between semantic dementia (SD) and primary progressive aphasia (PPA) has been the subject of debate ever since the syndromes were first described, in converging streams of research from the neuropsychological and neurologic communities. The most salient clinical features of SD are anomia with circumlocution and semantic paraphasia, single-word comprehension deficit, and reduced category fluency. Of critical importance is the fact that patients also show deficits on non-verbal tasks using visual, auditory, and other modalities, suggesting that the key impairment in SD is a breakdown in conceptual knowledge rather than a specific problem with language. The finding of item consistency between the various tests supports this view. The order in which the features appear can be explained by the variable degree of redundancy in access to semantic knowledge from the different perceptual modalities. Atrophy is seen in the anterior and inferior temporal lobe rather than in classic language areas, further distancing SD from aphasic syndromes. Semantic dementia and progressive non-fluent aphasia (PNFA) share some clinical and pathologic characteristics with frontal variant frontotemporal dementia, but there are also clear differences between the three syndromes. We believe that many patients described as having fluent primary progressive aphasia in fact have early SD. Semantic dementia is a well-defined syndrome, distinct from PNFA but related to it within the spectrum of frontotemporal lobar degeneration syndromes.

Aphasia, Primary Progressive↗

PubMed1994

Morphological errors and the representation of morphology in the lexical-semantic system.

Neuropsychological studies support the hypothesis that morphology is represented autonomously, both at the level of word meaning and at the level of word form. In output processes, morphologically organized semantic information activates lexical representations of roots and affixes, which are composed before production. In input processes, the stimulus is parsed along the morphological dimension, to access root and affix lexical representations, which in turn activate morphologically organized semantic information. Inflectional and derivational morphology are represented independently in the lexicon. Inflected words are fully decomposed; derived words are decomposed into base form+inflection. In aphasia, morphological errors in transcoding tasks always co-occur with semantic and/or phonemic errors. Morphological errors in transcoding tasks require combined damage to morphological representations in the semantic-lexical system and to sublexical conversion procedures; they co-occur with semantic errors when also root representations are damaged. The co-occurrence of morphological and phonemic errors can be accounted for by several hypotheses, but its theoretical meaning is still uncertain.

Aphasia↗

PubMed2004

Semantic graphs and associative memories.

Graphs have been increasingly utilized in the characterization of complex networks from diverse origins, including different kinds of semantic networks. Human memories are associative and are known to support complex semantic nets; these nets are represented by graphs. However, it is not known how the brain can sustain these semantic graphs. The vision of cognitive brain activities, shown by modern functional imaging techniques, assigns renewed value to classical distributed associative memory models. Here we show that these neural network models, also known as correlation matrix memories, naturally support a graph representation of the stored semantic structure. We demonstrate that the adjacency matrix of this graph of associations is just the memory coded with the standard basis of the concept vector space, and that the spectrum of the graph is a code invariant of the memory. As long as the assumptions of the model remain valid this result provides a practical method to predict and modify the evolution of the cognitive dynamics. Also, it could provide us with a way to comprehend how individual brains that map the external reality, almost surely with different particular vector representations, are nevertheless able to communicate and share a common knowledge of the world. We finish presenting adaptive association graphs, an extension of the model that makes use of the tensor product, which provides a solution to the known problem of branching in semantic nets.

Journal Article↗

PubMed1998

Integration of clinical information across patient records: a comparison of mechanisms used to enforce semantic coherence.

Semantic coherence about clinical information is the bottleneck for true interoperability among applications in health telematics. Healthcare records are in principle made of statements about patient's health and activities performed, organized within attested transactions or messages. Various mechanisms were developed to optimally represent details of statements into a record system, creating de facto three subdivisions: 1) "containers" of clinical information, i.e., section headings, data elements in local records; segments and data fields in messages; 2) their "contents," i.e., coding systems and terminologies; and 3) "transaction context," i.e., circumstances related to document production and message exchange, typically represented in their headers. Details rely on a common semantic background and should therefore, be seen in a continuum; nevertheless, design methodologies and tools for the three subdivisions evolved independently and assignment of details to subdivisions is not predetermined by principles, but depends on implementation issues. Recent developments within the European Committee for Standardization (CEN/TC251/WG II) and in the European Project GALEN-IN-USE provide a new insight on semantics in healthcare. In order to guide harmonization of semantic aspects in the different series of standards--in information models, messages, document markup, terminology systems--we present here a comparison of the various mechanisms they use to enforce semantic coherence on clinical information.

Computer Communication Networks↗

PubMed1999

Semantic integration in sentences and discourse: evidence from the N400.

In two ERP experiments we investigated how and when the language comprehension system relates an incoming word to semantic representations of an unfolding local sentence and a wider discourse. In Experiment 1, subjects were presented with short stories. The last sentence of these stories occasionally contained a critical word that, although acceptable in the local sentence context, was semantically anomalous with respect to the wider discourse (e.g., Jane told the brother that he was exceptionally slow in a discourse context where he had in fact been very quick). Relative to coherent control words (e.g., quick), these discourse-dependent semantic anomalies elicited a large N400 effect that began at about 200 to 250 msec after word onset. In Experiment 2, the same sentences were presented without their original story context. Although the words that had previously been anomalous in discourse still elicited a slightly larger average N400 than the coherent words, the resulting N400 effect was much reduced, showing that the large effect observed in stories depended on the wider discourse. In the same experiment, single sentences that contained a clear local semantic anomaly elicited a standard sentence-dependent N400 effect (e.g., Kutas &Hillyard, 1980). The N400 effects elicited in discourse and in single sentences had the same time course, overall morphology, and scalp distribution. We argue that these findings are most compatible with models of language processing in which there is no fundamental distinction between the integration of a word in its local (sentence-level) and its global (discourse-level) semantic context.

Adult↗

PubMed2002

Towards a semantic medical Web: HealthCyberMap's tool for building an RDF metadata base of health information resources based on the Qualified Dublin Core Metadata Set.

BACKGROUND: HealthCyberMap (http://healthcybermap.semanticweb.org/) aims at mapping Internet health information resources in novel ways for enhanced retrieval and navigation. This is achieved by collecting appropriate resource metadata in an unambiguous form that preserves semantics. MATERIAL/METHODS: We modelled a qualified Dublin Core (DC) metadata set ontology with extra elements for resource quality and geographical provenance in Prot g -2000. A metadata collection form helps acquiring resource instance data within Prot g . The DC subject field is populated with UMLS terms directly imported from UMLS Knowledge Source Server using UMLS tab, a Prot g -2000 plug-in. The project is saved in RDFS/RDF. RESULTS: The ontology and associated form serve as a free tool for building and maintaining an RDF medical resource metadata base. The UMLS tab enables browsing and searching for concepts that best describe a resource, and importing them to DC subject fields. The resultant metadata base can be used with a search and inference engine, and have textual and/or visual navigation interface(s) applied to it, to ultimately build a medical Semantic Web portal. Different ways of exploiting Prot g -2000 RDF output are discussed. CONCLUSIONS: By making the context and semantics of resources, not merely their raw text and formatting, amenable to computer 'understanding,' we can build a Semantic Web that is more useful to humans than the current Web. This requires proper use of metadata and ontologies. Clinical codes can reliably describe the subjects of medical resources, establish the semantic relationships (as defined by underlying coding scheme) between related resources, and automate their topical categorisation.

Humans↗

PubMed2002

The semantic metadatabase (SEMEDA): ontology based integration of federated molecular biological data sources.

A system for "intelligent" semantic integration and querying of federated databases is being implemented by using three main components: A component which enables SQL access to integrated databases by database federation (MARGBench), an ontology based semantic metadatabase (SEMEDA) and an ontology based query interface (SEMEDA-query). In this publication we explain and demonstrate the principles, architecture and the use of SEMEDA. Since SEMEDA is implemented as 3 tiered web application database providers can enter all relevant semantic and technical information about their databases by themselves via a web browser. SEMEDA' s collaborative ontology editing feature is not restricted to database integration, and might also be useful for ongoing ontology developments, such as the "Gene Ontology" [2]. SEMEDA can be found at http://www-bm.cs.uni-magdeburg.de/semeda/. We explain how this ontologically structured information can be used for semantic database integration. In addition, requirements to ontologies for molecular biological database integration are discussed and relevant existing ontologies are evaluated. We further discuss how ontologies and structured knowledge sources can be used in SEMEDA and whether they can be merged supplemented or updated to meet the requirements for semantic database integration.

Databases, Genetic↗

PubMed1996

Dissimilar age influences on two ERP waveforms (LPC and N400) reflecting semantic context effect.

Age-related changes in semantic context effects were examined using late event-related brain potentials (ERPs). Auditory ERPs to semantically congruous and incongruous final words in spoken sentences were recorded in 16 children (aged 5-11 years) and 16 adults. Previous findings concerning age-related effects on N400 were replicated: the N400 effect was significantly larger in children than in adults. The main new finding was that a late positive component (LPC) following N400 and modulated by semantic context in adults was not found in children. Thus, the common generalization that semantic context effects decline with age holds only for ERP components occurring in the N400 time window or earlier. The cognitive function reflected by the semantic LPC we observed is not clear, but it seems to have a role different from that of the N400, although in adults the components often co-exist as an N400-LPC complex.

Aging↗

PubMed2000

Impairment of semantic knowledge in Parkinson disease.

BACKGROUND: Parkinson disease (PD) is commonly characterized by cognitive deterioration, but it is still unclear whether PD is associated with semantic impairments. OBJECTIVE: To evaluate semantic knowledge of concepts in patients with idiopathic PD, addressing concrete and abstract concepts, conceptual attributes, and conceptual relations. METHODS: Twelve patients with preserved cognitive status, 12 patients with mildly deteriorated cognitive status, and 12 control subjects were studied. The cognitive status of patients and controls was determined using detailed cognitive testing. Patients were participants in a university-based movement disorder program, and their PD diagnoses were clinically confirmed during long-term follow-up. The 2 patient groups were similar in age, level of education, disease duration, and parkinsonian disability. Patients were required to produce verbal descriptions of concrete and abstract concepts, to give ratings of the importance of concept attributes, and to assess and construct conceptual hierarchies. The description tasks included guiding questions, which were used if the spontaneous productions of the patients lacked any essentials expected in the answers. RESULTS: Patients with mild cognitive deterioration performed less well than the other groups in defining concrete and abstract concepts (P<.001 for both). External guidance did not help them markedly improve their performance. They also had difficulties in tasks calling for knowledge of the importance of given attributes to the concepts and in tasks demanding evaluation of hierarchical semantic relations between concepts (P<.001 for both). CONCLUSION: Semantic disruption is implied in idiopathic PD in association with incipient cognitive impairment.

Aged↗

PubMed1979

The semantic perception of life, death and suicide.

Gathered semantic distance scores between pairs of concepts (life and death, life and suicide, and death and suicide) from suicidal, psychosomatic, and hospitalized patients (N = 45). It was hypothesized that suicidal individuals would show greater semantic identity between these concepts than would the other patients. It was thought that such semantic identity on the part of the other patients. It was thought that such semantic identity on the part of the suicidal individuals would reflect their inability to discriminate between these concepts. However, it was found that the suicidal individuals differentiated between life and death to a significantly greater degree than did the comparison groups. It may be that suicidal decisions are based more on being confronted by definite clear alternative states of existence than by confusion between them.

Adult↗

PubMed2003

Involvement of the cerebellum in semantic discrimination: an fMRI study.

We investigated, using functional magnetic resonance imaging (fMRI), whether semantic discrimination, an inner linguistic task without overt articulation, can elicit activation in the cerebellum. Six subjects performed three semantic tasks with different loads of discrimination while being scanned. All three semantic tasks activated distributed brain areas, including the right posterior inferior cerebellum. Much stronger activation was found in the cerebellum in more difficult tasks, in terms of the activation volume and signal intensity. These results suggest that the cerebellum activation is involved in semantic discrimination and is modulated by discrimination difficulty.

Adult↗

PubMed2004

Separating phonological and semantic processing in auditory sentence processing: a high-resolution event-related brain potential study.

Phonological and semantic processing was studied using high-resolution event-related brain potentials (ERPs) during a sentence-matching task to investigate the spatial distribution of the phonological mismatch negativity (PMN) and the N400 response. It was hypothesized that the two components were spatially separable and that the activity matched prior localization knowledge. Participants examined visual-auditory sentence pairs that related within a semantic hierarchy (e.g., visual: "The man is teaching in the classroom"; Auditory: "The man is in the em leader school/barn"). Semantic congruency was varied for the final words of the spoken sentences. Incongruent words mismatched expectation in terms of both the initial phonological features (unexpected sound) and semantic features (unexpected meaning). In addition, the category-exemplar probability of the final words was either high or low, with low probability words being more difficult to anticipate. Low probability words were predicted to selectively affect PMN activity. We found that incongruent words elicited a PMN (287 msec) and a N400 (424 msec), for both the high and low probability words. As expected, low probability congruent words elicited a small PMN but no N400. In contrast, high probability congruent words elicited neither a detectible PMN nor a N400. The primary PMN sources were in left inferior frontal and inferior parietal lobes. The primary N400 source activation occurred along the left perisylvian cortex, consistent with prior N400 source localization work. From these results, it was concluded that the PMN and N400 were localized to separate cortical language (and memory) regions and had different source activation patterns.

Adult↗

PubMed2004

Variability of fMRI activation during a phonological and semantic language task in healthy subjects.

Assessing inter-individual variability of functional activations is of practical importance in the use of functional magnetic resonance imaging (fMRI) in a clinical context. In this fMRI study we addressed this issue in 30 right-handed, healthy subjects using rhyme detection (phonologic) and semantic categorization tasks. Significant activations, found mainly in the left hemisphere, concerned the inferior frontal gyrus, the superior/middle temporal gyri, the prefrontal cortex, the inferior parietal lobe, the superior parietal lobule/superior occipital gyrus, the pre-central gyrus, and the supplementary motor area. Intensity/spatial analysis comparing activations in both tasks revealed an increased involvement of frontal regions in the semantic task and of temporo-parietal regions in the phonologic task. The frequency of activation analyzed in nine regional subdivisions revealed a high inter-subject variability but showed that the most frequently activated regions were the inferior frontal gyrus and the prefrontal cortex. Laterality indices, strongly lateralizing in both tasks, were slightly higher in the semantic (0.76 +/- 0.19) than the phonologic task (0.66 +/- 0.27). Frontal dominance indices (a measure of frontal vs. posterior left hemisphere dominance) indicated more robust frontal activations in the semantic than the phonologic task. Our study allowed the characterization of the most frequently involved foci in two language tasks and showed that the combination of these tasks constitutes a suitable tool for determining language lateralization and for mapping major language areas.

Adult↗

PubMed2005

Brain activation during semantic judgment of Chinese sentences: A functional MRI study.

A functional magnetic resonance imaging (fMRI) study was conducted to investigate whether the anatomic substrates of semantic memory may reflect categorical organization and to determine whether the left middle frontal gyrus (Brodmann area [BA] 9) plays a role in Chinese semantic judgment. Unlike previous studies using a word-retrieval task (e.g., word generation, naming, and word categorization), we used a typical task of semantic knowledge retrieval in cognitive psychology in which subjects were asked to determine whether a sentence describing an attribute of living things or nonliving things was true or not. The experimental conditions evoked extensive activation over several regions of the brain including a very strong activation in the left middle frontal region (BA9 and BA46). Our data show that there is no unique activation associated with living or nonliving things at the statistical threshold used in our study. The results imply that human semantic system is undifferentiated by category at the neural level. Our findings also corroborate and extend the claim that the left middle frontal gyrus plays an important role in reading Chinese at both the sentence and the word level.

Adolescent↗

PubMed1993

Impairments of lexical-semantic processing in aphasia: evidence from the processing of lexical ambiguities.

Broca's and Wernicke's aphasics performed speeded lexical decisions on the third member of auditorily presented triplets consisting of two word primes followed by either a word or a nonword. In three of the four priming conditions, the second prime was a homonym with two unrelated meanings. The relation of the first prime and the target with the two meanings of the homonym was manipulated in the different priming conditions. The two readings of the ambiguous words either shared their grammatical form class (noun-noun ambiguities) or not (noun-verb ambiguities). The silent intervals between the members of the triplets were varied between 100, 500, and 1250 msec. Priming at the shortest interval is mainly attributed to automatic lexical processing, and priming at the longest interval is mainly due to forms of controlled lexical processing. For both Broca's and Wernicke's aphasics overall priming effects were obtained at ISIs of 100 and 500 msec, but not at an ISI of 1250 msec. This pattern of results is consistent with the view that both types of aphasics can automatically access the semantic lexicon, but might be impaired in integrating lexical-semantic information into the context. Broca's aphasics showed a specific impairment in selecting the contextually appropriate reading of noun-verb ambiguities, which is suggested to result from a failure either in the on-line morphological parsing of complex word forms into a stem and an inflection or in the on-line exploitation of the syntactic implications of the inflectional suffix. In a final experiment patients were asked to explicitly judge the semantic relations between a subset of the primes that were used in the lexical decision study. Wernicke's aphasics performed worse than both Broca's aphasics and normal controls, indicating a specific impairment for these patients in consciously operating on automatically accessed lexical-semantic information.

Aged↗

PubMed1996

Brain functional profiles in formal and semantic fluency tasks: a SPECT study in normals.

SPECT method is used to analyze changes in regional cerebral blood flow in a group of 19 normal subjects during a baseline task (repetition of two words) and two verbal fluency tasks, a semantic fluency and a formal fluency. The semantic fluency task was associated with a relative CBF increase in the right dorso-lateral and medial frontal region when compared with that seen in the baseline condition. No specific activation was found for the formal fluency task compared to that seen in the baseline task. We suggest that the activation of the right frontal region reflects semantic categorization strategies in semantic fluency. The lack of activation of the left frontal region may be due to an activation induced by the nature of the baseline task (i.e., a self-paced repetition task).

Adult↗

PubMed1996

Preserved semantic priming effect in alexia.

BH, a left-handed patient with alexia and nonfluent aphasia, was presented with a lexical-decision task in which words and pronounceable pseudowords were preceded by semantically related or unrelated picture primes (Experiment 1). In Experiment 2, BH was given an explicit reading task using the word lists from Experiment 1. Performance on Experiment 2 disclosed severe reading deficits in both oral reading and semantic matching of the words to pictures. However, in Experiment 1, BH demonstrated a significant semantic priming effect, responding more accurately and more quickly to words preceded by related primes than by unrelated primes. The present results suggest that even in a patient with severe alexia, implicit access to semantic information can be preserved in the absence of explicit identification. The possibility of categorical gradient in implicit activation (living vs. nonliving) in BH was also discussed, which, however, needs to be clarified in the further investigation.

Brain↗