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PubMed1976

[Verbal and non-verbal aspects of semantic disintegration in aphasia (author's transl)].

After a review of the explanations offered in the literature on the nature of aphasic disintegration, the author suggests that a nuclear impairment of semantic level of language integration may exist in many forms of aphasia. This hypothesis is supported by personal observations on verbal and non-verbal aspects of semantic impairment in aphasia. The incidence of semantic troubles is very high both at the level of verbal production and comprehension and at a non-verbal study of the "areas of meaning". No relationship was found between the incidence of semantic troubles and the ("fluent" or "non-fluent") clinical form of aphasia. A definite relationship exists between production of semantic paraphasias at the expressive level and number of semantic errors obtained as a verbal comprehension task, and between verbal semantic disorders and pathological performances at the non-verbal task of "semantic relationships".

Aphasia↗

PubMed2004

Evidence for semantic learning in profound amnesia: an investigation with patient H.M.

Until recently, it seemed unlikely that any semantic knowledge could be acquired following extensive bilateral damage to the medial temporal lobes (MTL). Although recent studies have demonstrated some semantic learning in amnesic patients, questions remain regarding the limits of this capacity and the extent to which it relies on those patients' residual MTL function. The present study examined whether detailed, semantic memory could be acquired by a patient with no functioning hippocampus. We used cued recall and forced-choice recognition tasks to investigate whether the patient H.M. had acquired knowledge of people who became famous after the onset of his amnesia. Results revealed that, with first names provided as cues, he was able to recall the corresponding famous last name for 12 of 35 postoperatively famous personalities. This number nearly doubled when semantic cues were added, suggesting that his knowledge of the names was not limited to perceptual information, but was incorporated in a semantic network capable of supporting explicit recall. In forced-choice recognition, H.M. discriminated 87% of postmorbid famous names from foils. Critically, he was able to provide uniquely identifying semantic facts for one-third of these recognized names, describing John Glenn, for example, as "the first rocketeer" and Lee Harvey Oswald as a man who "assassinated the president." Although H.M.'s semantic learning was clearly impaired, the results provide robust, unambiguous evidence that some new semantic learning can be supported by structures beyond the hippocampus proper.

Aged↗

PubMed2005

SOA-dependent N400 and P300 semantic priming effects using pseudoword primes and a delayed lexical decision.

In a previous semantic priming study, we found a semantic distance effect on the lexical-decision-related P300 when SOA was short (150 ms) only, but no different RT and N400 priming effects between short and long (700 ms) SOAs. To investigate this further, we separated priming from lexical decision, using a delayed lexical decision in the present study. In the short SOA only, primed targets evoked an early peaking (approximately 480 ms) P300-like component, probably because the subject detected the semantic relationship implicitly. We hypothesize that in tasks requiring an immediate lexical decision, this early P300 and the later lexical decision P300 (approximately 600 ms) are additive. Secondly, we found both a direct and an indirect priming effect for both SOAs for the ERP amplitude of the N400 time window. However the N400 component itself was considerably larger in the long SOA than in the short SOA. We interpreted this finding as an ERP correlate for deeper semantic processing in the long SOA, due to increased attention that was provoked by the use of pseudoword primes. In contrast, in the short SOA, subjects might have used a shallowed semantic processing. N400, P300, and RTs are sensitive to semantic priming-but the modulation patterns are not consistent. This raises the question as to which variable reflects an immediate physiological correlate of semantic priming, and which variable reflects co-occurring processes associated with semantic priming.

Adult↗

PubMed2003

An fMRI study of semantic processing in men with schizophrenia.

As a means toward understanding the neural bases of schizophrenic thought disturbance, we examined brain activation patterns in response to semantically and superficially encoded words in patients with schizophrenia. Nine male schizophrenic and 9 male control subjects were tested in a visual levels of processing (LOP) task first outside the magnet and then during the fMRI scanning procedures (using a different set of words). During the experiments visual words were presented under two conditions. Under the deep, semantic encoding condition, subjects made semantic judgments as to whether the words were abstract or concrete. Under the shallow, nonsemantic encoding condition, subjects made perceptual judgments of the font size (uppercase/lowercase) of the presented words. After performance of the behavioral task, a recognition test was used to assess the depth of processing effect, defined as better performance for semantically encoded words than for perceptually encoded words. For the scanned version only, the words for both conditions were repeated in order to assess repetition-priming effects. Reaction times were assessed in both testing scenarios. Both groups showed the expected depth of processing effect for recognition, and control subjects showed the expected increased activation of the left inferior prefrontal cortex (LIPC) under semantic encoding relative to perceptual encoding conditions as well as repetition priming for semantic conditions only. In contrast, schizophrenics showed similar patterns of fMRI activation regardless of condition. Most striking in relation to controls, patients showed decreased LIFC activation concurrent with increased left superior temporal gyrus activation for semantic encoding versus shallow encoding. Furthermore, schizophrenia subjects did not show the repetition priming effect, either behaviorally or as a decrease in LIPC activity. In patients with schizophrenia, LIFC underactivation and left superior temporal gyrus overactivation for semantically encoded words may reflect a disease-related disruption of a distributed frontal temporal network that is engaged in the representation and processing of meaning of words, text, and discourse and which may underlie schizophrenic thought disturbance.

Adult↗

PubMed2002

The cohesive metaschema: a higher-level abstraction of the UMLS Semantic Network.

The Unified Medical Language System (UMLS) joins together a group of established medical terminologies in a unified knowledge representation framework. Two major resources of the UMLS are its Metathesaurus, containing a large number of concepts, and the Semantic Network (SN), containing semantic types and forming an abstraction of the Metathesaurus. However, the SN itself is large and complex and may still be difficult to view and comprehend. Our structural partitioning technique partitions the SN into structurally uniform sets of semantic types based on the distribution of the relationships within the SN. An enhancement of the structural partition results in cohesive, singly rooted sets of semantic types. Each such set is named after its root which represents the common nature of the group. These sets of semantic types are represented by higher-level components called metasemantic types. A network, called a metaschema, which consists of the meta-semantic types connected by hierarchical and semantic relationships is obtained and provides an abstract view supporting orientation to the SN. The metaschema is utilized to audit the UMLS classifications. We present a set of graphical views of the SN based on the metaschema to help in user orientation to the SN. A study compares the cohesive metaschema to metaschemas derived semantically by UMLS experts.

Algorithms↗

PubMed2004

The human perirhinal cortex and semantic memory.

Studies in macaque monkeys indicate that the perirhinal cortex in the temporal lobe participates in object memory. This function may be analogous to aspects of human semantic memory (knowledge of objects, concepts, faces and words). To date, the status of perirhinal cortex has not specifically been investigated in patients with semantic deficits as seen in semantic dementia, the temporal lobe variant of frontotemporal dementia. High-resolution three-dimensional magnetic resonance imaging was performed in subjects with semantic dementia and Alzheimer's disease (characterized in its early stages by selective episodic memory impairment) and in healthy age-matched controls. Hippocampal, perirhinal, temporopolar and entorhinal cortex volumes were measured by outlining areas on successive scan slices according to recognized landmarks. The entorhinal and hippocampal regions were further subdivided into anterior and posterior parts. In keeping with the hypothesized contribution of the perirhinal cortex to semantic memory function, we found greater involvement of this region, together with the temporopolar and anterior entorhinal cortices, in semantic dementia than in either Alzheimer's disease patients or control subjects. Performance on a range of semantic tests also correlated with perirhinal volume. Bilateral reduction in hippocampal volume compared with controls was seen in Alzheimer's disease. In conclusion, atrophy of the human perirhinal cortex, and of directly connected areas, was associated with semantic memory impairment but not episodic memory impairment, as predicted from the primate work.

Aged↗

PubMedDate not supplied

Access to semantic memory in Parkinson's disease and multiple sclerosis.

The capacity to access semantic memory and the efficiency of the memory search were studied in patients with Parkinson's disease (PD) or multiple sclerosis (MS) using a modified version of the "Supermarket Test." PD and MS patients who performed normally on the Boston Naming Test generated as many specific exemplars and category labels as did controls, and these patients also searched their semantic memories as efficiently as controls. In contrast, PD and MS patients with impaired confrontational naming generated fewer specific exemplars, but a normal number of generic category labels. These naming-impaired patients searched their semantic memories less efficiently than controls. For both MS and PD patients, the efficiency of semantic memory search was significantly correlated with measures that reflect access to semantic memory (eg, performance on letter or category fluency tasks), but was not significantly related to measures of problem-solving ability derived from the Wisconsin Card Sorting Test. Inefficient search of semantic memory in MS and PD appears to arise from an inability to retrieve knowledge from semantic memory quickly or from the loss of information from semantic memory stores, rather than from impairment in the ability to formulate and deploy appropriate strategies for task solution.

Aged↗

PubMed2001

Patterns of temporal lobe atrophy in semantic dementia and Alzheimer's disease.

Volumetric magnetic resonance imaging analyses of 30 subjects were undertaken to quantify the global and temporal lobe atrophy in semantic dementia and Alzheimer's disease. Three groups of 10 subjects were studied: semantic dementia patients, Alzheimer's disease patients, and control subjects. The temporal lobe structures measured were the amygdala, hippocampus, entorhinal cortex, parahippocampal gyrus, fusiform gyrus, and superior, middle, and inferior temporal gyri. Semantic dementia and Alzheimer's disease groups did not differ significantly on global atrophy measures. In semantic dementia, there was asymmetrical temporal lobe atrophy, with greater left-sided damage. There was an anteroposterior gradient in the distribution of temporal lobe atrophy, with more marked atrophy anteriorly. All left anterior temporal lobe structures were affected in semantic dementia, with the entorhinal cortex, amygdala, middle and inferior temporal gyri, and fusiform gyrus the most severely damaged. Asymmetrical, predominantly anterior hippocampal atrophy was also present. In Alzheimer's disease, there was symmetrical atrophy of the entorhinal cortex, hippocampus, and amygdala, with no evidence of an anteroposterior gradient in the distribution of temporal lobe or hippocampal atrophy. These data demonstrate that there is a marked difference in the distribution of temporal lobe atrophy in semantic dementia and Alzheimer's disease. In addition, the pattern of atrophy in semantic dementia suggests that semantic memory is subserved by anterior temporal lobe structures, within which the middle and inferior temporal gyri may play a key role.

Aged↗

PubMed2006

Developmental and skill effects on the neural correlates of semantic processing to visually presented words.

Functional magnetic resonance imaging (fMRI) was used to explore the neural correlates of semantic judgments to visual words in a group of 9- to 15-year-old children. Subjects were asked to indicate if word pairs were related in meaning. Consistent with previous findings in adults, children showed activation in bilateral inferior frontal gyri (Brodmann area [BA] 47, 45) and left middle temporal gyrus (BA 21). Words with strong semantic association elicited significantly greater activation in bilateral inferior parietal lobules (BA 40), suggesting stronger integration of highly related semantic features. By contrast, words with weak semantic association elicited greater activation in left inferior frontal gyrus (BA 45) and middle temporal gyrus (BA 21), suggesting more difficult feature search and more extensive access to semantic representations. We also examined whether age and skill explained unique variance in the patterns of activation. Increasing age was correlated with greater activation in left middle temporal gyrus (BA 21) and inferior parietal lobule (BA 40), suggesting that older children have more elaborated semantic representations and more complete semantic integration processes, respectively. Decreasing age was correlated with activation in right superior temporal gyrus (BA 22) and decreasing accuracy was correlated with activation in right middle temporal gyrus (BA 21), suggesting the engagement of ancillary systems in the right hemisphere for younger and lower-skill children.

Adolescent↗

PubMed2007

Dissociating stimulus-driven semantic and phonological effect during reading and naming.

The aim of the present study was to dissociate the neural correlates of semantic and phonological processes during word reading and picture naming. Previous studies have addressed this issue by contrasting tasks involving semantic and phonological decisions. However, these tasks engage verbal short-term memory and executive functions that are not required for reading and naming. Here, 20 subjects were instructed to overtly name written words and pictures of objects while their neuronal responses were measured using functional magnetic resonance imaging (fMRI). Each trial consisted of a pair of successive stimuli that were either semantically related (e.g., "ROBIN-nest"), phonologically related (e.g., "BELL-belt"), unrelated (e.g., "KITE-lobster"), or semantically and phonologically identical (e.g., "FRIDGE-fridge"). In addition, a pair of stimuli could be presented in either the same modality (word-word or picture-picture) or a different modality (word-picture or picture-word). We report that semantically related pairs modulate neuronal responses in a left-lateralized network, including the pars orbitalis of the inferior frontal gyrus, the middle temporal gyrus, the angular gyrus, and the superior frontal gyrus. We propose that these areas are involved in stimulus-driven semantic processes. In contrast, phonologically related pairs modulate neuronal responses in bilateral insula. This region is therefore implicated in the discrimination of similar, competing phonological and articulatory codes. The above effects were detected with both words and pictures and did not differ between the two modalities even with a less conservative statistical threshold. In conclusion, this study dissociates the effects of semantic and phonological relatedness between successive items during reading and naming aloud.

Adolescent↗

PubMed1996

Introduction. The investigation of lexical semantic representation in Alzheimer's disease.

The study of lexical semantic representation is central to an understanding of brain and language. In Alzheimer's disease, neuropathological alterations consistently involve neocortical areas in which lexical semantic information is represented, and patients with this common dementing disorder evince priminent lexical semantic disturbances. General issues concern the establishment of new semantic memories, the manner in which meaning is represented within the lexicon, the retrieval of semantic information from the lexicon, and the relation between lexical semantics and nonlinguistic cognitive processes. Studies of lexical semantic representation in patients with Alzheimer's disease are especially informative in considering all but the first of these key issues.

Aged↗

PubMed1999

Functional specialization for semantic and phonological processing in the left inferior prefrontal cortex.

Neuroimaging and neuropsychological studies have implicated left inferior prefrontal cortex (LIPC) in both semantic and phonological processing. In this study, functional magnetic resonance imaging was used to examine whether separate LIPC regions participate in each of these types of processing. Performance of a semantic decision task resulted in extensive LIPC activation compared to a perceptual control task. Phonological processing of words and pseudowords in a syllable-counting task resulted in activation of the dorsal aspect of the left inferior frontal gyrus near the inferior frontal sulcus (BA 44/45) compared to a perceptual control task, with greater activation for nonwords compared to words. In a direct comparison of semantic and phonological tasks, semantic processing preferentially activated the ventral aspect of the left inferior frontal gyrus (BA 47/45). A review of the literature demonstrated a similar distinction between left prefrontal regions involved in semantic processing and phonological/lexical processing. The results suggest that a distinct region in the left inferior frontal cortex is involved in semantic processing, whereas other regions may subserve phonological processes engaged during both semantic and phonological tasks.

Brain Mapping↗

PubMed2002

Retrieval of visual, auditory, and abstract semantics.

Conceptual knowledge is thought to be represented in a large distributed network, indexing a range of different semantic features (e.g., visual, auditory, functional). We investigated the anatomical organization of these features, using PET, by contrasting brain activity elicited by heard words with (i) visual (e.g., blue), (ii) auditory (e.g., noise), or (iii) abstract (e.g., truth) meaning. The activation task was either repetition or semantic decision (e.g., does the meaning of the word relate to religion?). In the baseline conditions, the sound track of the words was reversed and subjects had to say "OK" (control for repetition) or make an acoustic decision (control for semantic decision). Irrespective of task, words relative to their corresponding controls activated the left posterior inferior temporal and inferior frontal cortices. In addition, semantic decisions on words with sensory (visual and auditory) meanings enhanced activation in a ventral region of the left anterior temporal pole. These results are consistent with neuropsychological studies showing that anterior temporal lobe damage can cause deficits for items that are mainly defined by their sensory features (i.e., concrete, particularly living items). Since modality-specific activation was observed only during the semantic decision task, we discuss whether it reflects retrieval of sensory semantics per se or the degree to which semantic associations are triggered during effortful retrieval.

Adult↗

PubMed2002

The effects of associative and semantic priming in the lexical decision task.

Four lexical decision experiments were conducted to examine under which conditions automatic semantic priming effects can be obtained. Experiments 1 and 2 analyzed associative/semantic effects at several very short stimulus-onset asynchronies (SOAs), whereas Experiments 3 and 4 used a single-presentation paradigm at two response-stimulus intervals (RSIs). Experiment 1 tested associatively related pairs from three semantic categories (synonyms, antonyms, and category coordinates). The results showed reliable associative priming effects at all SOAs. In addition, the correlation between associative strength and magnitude of priming was significant only at the shortest SOA (66 ms). When prime-target pairs were semantically but not associatively related (Experiment 2), reliable priming effects were obtained at SOAs of 83 ms and longer. Using the single-presentation paradigm with a short RSI (200 ms, Experiment 3), the priming effect was equal in size for associative + semantic and for semantic-only pairs (a 21-ms effect). When the RSI was set much longer (1,750 ms, Experiment 4), only the associative + semantic pairs showed a reliable priming effect (23 ms). The results are interpreted in the context of models of semantic memory.

Association Learning↗

PubMed1994

Episodic and semantic memory: an analysis in the EEG theta and alpha band.

This study examines the hypothesis that in contrast to semantic memory processes that are assumed to be reflected primarily within the alpha band, episodic memory processes are related to activity within the theta band. EEG signals were recorded from subjects as they performed a semantic congruency and an episodic recognition task. In the semantic task, subjects had to judge whether or not sequentially presented concept-feature pairs (such as "eagle-claws" or "pea-huge") are semantically congruent. In the episodic task, which followed the semantic task without prior warning, the same word pairs were presented together with new distractors (generated by repairing known concept-feature pairs). Here, subjects judged whether or not a particular concept-feature pair was already presented during the semantic task. EEG data were analyzed using event-related desynchronization (ERD) as a measure for the amount of event-related changes in band power in the theta band and in the upper and lower alpha bands. The alpha band was determined individually, using the alpha peak frequency during the resting period as the cut-off point to separate the lower from the upper alpha band. The results, which are based on those identical word pairs that demanded a yes response in both tasks, showed that semantic memory processes are indeed primarily reflected in the upper alpha band whereas episodic memory processes are reflected in the theta band. The possible relationship between hippocampal theta activity and the encoding of episodic information is discussed.

Adult↗

PubMed1986

Semantic impairment and anomia in Alzheimer's disease.

Impairment in naming visually presented objects was investigated in patients with a clinical diagnosis of Alzheimer's disease. Impaired object naming correlated with difficulty listing the names of objects from a specified semantic category and with erroneous selection of words semantically related to the correct names for objects in a name recognition test. These results suggest that patients with Alzheimer's disease have a semantic impairment characterized by inability to distinguish among objects that are members of the same semantic category, and that this impairment is associated with difficulty producing the names for objects. Semantic impairment was present in patients with normal ability to discriminate visually presented shapes, indicating that the semantic deficit in Alzheimer's disease occurs independently of abnormalities of visuospatial function. Patients tended to make errors on the same items in both confrontation naming and name recognition tests, suggesting that the semantic impairment in Alzheimer's disease involves loss of information about specific objects and their names.

Aged↗

PubMed2005

Semantic weight and verb retrieval in aphasia.

Individuals with agrammatic aphasia may have difficulty with verb production in comparison to nouns. Additionally, they may have greater difficulty producing verbs that have fewer semantic components (i.e., are semantically "light") compared to verbs that have greater semantic weight. A connectionist verb-production model proposed by Gordon and Dell (2003) learns through error correction to "divide the labor" between syntax and semantics. Verbs that are semantically heavier come to depend less on syntax and more on semantics. For lighter verbs, the reverse is true. We performed this study to clarify the role of semantic weight in aphasic verb production and to test the prediction from Gordon and Dell that a brain lesion that impairs the syntactic input to verb retrieval will impair lighter verbs more than heavier ones. Consistent with this prediction, we found that the decrement for lighter verbs was present in a group with agrammatic aphasia but not in a matched group without agrammatism.

Adult↗

PubMed2006

Semantic and syntactic processing in Chinese sentence comprehension: evidence from event-related potentials.

An ERP experiment was conducted to explore semantic and syntactic processes as well as their interplay in Chinese sentence comprehension. Participants were auditorily presented with Chinese ba sentences, which were either correct, semantically incorrect, syntactically incorrect, or both semantically and syntactically incorrect. The syntactic violation, which was created by eliminating the object-noun phrase from a preposition-object phrase structure, elicited an early starting anterior negativity which merged into a sustained negativity over anterior sites and a temporally limited centro-parietal negativity. The semantic violation elicited an early starting N400 effect. The combined violation in which the syntactic phrase structure violation and the semantic violation were crossed elicited an early staring sustained anterior negativity similar to the pure syntactic effect, and a centro-parietal negativity which was more negative than those of the syntactic condition and the semantic condition. No P600 was obtained neither for the syntactic nor for the combined condition. The results suggest that the syntactic processes (at about 50 ms) appear earlier than the semantic processes (at around 150 ms). They are independent from each other in the early time window (150-250 ms) but interact in a later processing phase (250-400 ms) during Chinese ba sentence comprehension. The broadly distributed negativity, which occurred during the N400 latency range observed in the three violation conditions, is thought to reflect thematic integration processes in the sentence-final position.

Adult↗