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PubMed2006

Temporo-prefrontal coordination increases when semantic associations are strongly encoded.

Relational association of disparate semantic concepts can strengthen encoding of episodes. Previous research has shown that the left medial temporal lobe (MTL) and the left prefrontal cortex (PFC) are the primary brain regions activated during both verbal encoding and the association of disparate semantic concepts. In the current functional magnetic resonance imaging (fMRI) study, our goal was to compare the coordinated response of the left MTL and left PFC when disparate semantic associations are strongly encoded compared to when they are weakly encoded. To achieve this goal, subjects were scanned while creating sentences based on a presented pair of words, and were asked to free-recall these sentences at a later time. Half the word pairs were semantically unrelated, and half were semantically related. Analysis of relatedness activations (unrelated-related contrast) suggested that the PFC was active whether or not the items were free-recalled, and increased activation of the MTL was required to promote encoding. Analyses of coordination of relatedness activations comparing free-recalled items to not free-recalled items showed an increase in left MTL-left PFC coordination for relatedness activations on free-recalled items. These results suggest that formation of relational semantic associations that lead to strongly encoded episodes requires increased coordination of the left MTL-left PFC neural pathway.

Adolescent↗

PubMed2006

Evidence for a dissociation of structural and semantic knowledge in dementia of the Alzheimer type (DAT).

Object recognition and naming deficits in dementia of the Alzheimer type (DAT) have typically been attributed to deficits in semantic processing, with only a few studies proposing loci of deficits other than semantic. One possible cause of DAT object recognition impairments could involve deficits in processing structural aspects of visually presented items. In this paper, we assess the performance of a group of mild DAT patients on two tasks of structural access, object decision, and the complete/incomplete task (based on part-whole matching task), as well as on a semantic probes task, designed to assess the patients' semantic knowledge of the same items for which structural knowledge had earlier been assessed. The DAT patients were substantially impaired in their performance on tasks of structural access. Further, no evidence for item-to-item consistency in the DAT patients' errors for the structural and semantic tasks was found, raising the possibility that structural and semantic knowledge may become differentially impaired in DAT.

Aged↗

PubMed2006

Semantic relevance, domain specificity and the sensory/functional theory of category-specificity.

According to the sensory/functional theory of semantic memory, Living items rely more on Sensory knowledge than Non-living ones. The sensory/functional explanation of category-specificity assumes that semantic features are organised on the basis of their content. We report here a study on DAT patients with impaired performance on Living items and tests of Sensory knowledge, and show that this impairment not only disappears after parcelling out semantic relevance, but is also reversed if this parameter is appropriately manipulated. Although semantic relevance model predicts these results [Sartori, G., & Lombardi, L. (2004). Semantic relevance and semantic disorders. Journal of Cognitive Neuroscience, 16, 439-452], they run counter to both the sensory/functional theory and the domain-specific theory of category-specific impairment.

Aged↗

PubMed2005

Disorganization of semantic memory underlies alogia in schizophrenia: an analysis of verbal fluency performance in Japanese subjects.

Patients with schizophrenia exhibit impaired semantic memory as well as deficits in a wide range of language-related functions, such as verbal fluency, comprehension and production of complex sentences. Since language and memory disturbances may underlie some of the psychotic symptoms of schizophrenia, the present study investigated the specific association between alogia (i.e. poverty of speech, poverty of content of speech, blocking, and increased latency of response) and semantic memory organization using the category fluency task (CFT) as a measure of verbal fluency. Thirty-eight patients with schizophrenia and an equal number of normal controls entered the study. Semantic structure was derived from multidimensional scaling analysis using sequential word outputs from the CFT. Patients with schizophrenia revealed disorganized semantic structure (e.g. irregular association of category members) compared with controls, consistent with previous reports. The patients were then divided into two groups, i.e. alogia- and non-alogia subjects, based on the Alogia scores from the Scale for the Assessment of Negative Symptoms (SANS). The symptom-based analysis showed that the semantic structure for the alogia group (Alogia score < or =2) was more disorganized than that for the non-alogia group (Alogia score <1) although the number of words produced did not differ between the two groups. The results of cluster analysis revealed the presence of bizarre coherence specifically in the alogia group. These results indicate that semantic memory disorganization may contribute to the symptom of alogia in schizophrenia. In addition, this is one of the few studies that examined verbal fluency in Japanese patients with schizophrenia and suggest that the language abnormalities in schizophrenia are universal.

Adult↗

PubMed2005

Are semantic deficits in schizophrenia due to problems with access or storage?

Semantic processing deficits are central to cognitive abnormalities in schizophrenia. Such semantic deficits may be related to either poor access or poor storage of semantic knowledge. 32 schizophrenia patients and 32 matched normal controls performed five semantic processing tasks that examined item-specific consistency over time, the word frequency effect and semantic priming. A subgroup of patients performed tasks on three separate occasions. It is generally assumed that a storage deficit is signalled by item-specific consistent performance, an exaggerated effect of word frequency, and the occurrence of hyperpriming; an access deficit is signalled by the absence of these effects. The data demonstrated item-specific consistency, a frequency effect and significant hyperpriming. The pattern is consistent with a storage deficit of semantic memory in schizophrenia.

Adult↗

PubMed2003

Automatic activation of the semantic network in schizophrenia: evidence from event-related brain potentials.

BACKGROUND: Language disorder associated with schizophrenia might be due to disturbances in both automatic activation and mechanisms of controlled attention. The contribution of each process to semantic memory dysfunction has not been determined for schizophrenia, and the semantic priming paradigm is well-suited for addressing this question. In the present report, event-related potentials (ERPs) elicited under conditions assumed to reveal automatic activation (short prime-target interval and low proportion of related words) are compared directly with ERPs elicited under conditions associated with controlled processing (long prime-target interval and high proportion of related words). METHODS: Visual ERPs were recorded during a lexical decision task, in which semantic relationship (associated and unassociated words), expectancy (relatedness proportions), and prime-target interval (250- and 850-msec inter-stimulus intervals [ISIs]) were varied. Diagnosis and expectancy were between-subjects factors; semantic relationship and ISI were repeated measures. The N400 priming effect (enhanced negativity to unassociated words) was compared between 34 male normal control subjects tested once and 37 male schizophrenia inpatients evaluated during their participation in a double-blind haloperidol maintenance therapy and placebo replacement protocol. RESULTS: The N400 priming effect for patients was significantly reduced during both pharmacologic phases, compared with controls. During haloperidol treatment, however, patients showed a significant N400 priming effect over the anterior scalp region and additionally under the automatic activation condition. The N400 priming effect was enhanced under the controlled processing condition for control subjects; this effect was not observed for patients. N400 amplitude elicited under the rapid presentation rate (250-msec ISI) differed between medicated patients and controls; groups did not differ for the 850-msec ISI. CONCLUSIONS: Findings suggest that automatic activation and mechanisms of controlled attention are both disrupted during semantic memory access for schizophrenia patients. Pharmacologic agents, such as haloperidol, might enhance automatic activation of the semantic network in this patient population, as indexed by the N400 component of the ERP.

Adult↗

PubMed2004

Evidence for a new conceptualization of semantic representation in the left and right cerebral hemispheres.

Two experiments are reported that examined qualitative differences in how semantic information is represented in the two hemispheres. In the first experiment, items that were associatively related but did not share semantic features or membership in semantic categories produced priming when delivered to the LH (RVF) but not to the RH (LVF). In the second experiment items that shared semantic features but were neither associates nor in the same category produced priming in the RH (LVF), but not in the LH (RVF). Together, the two experiments support the theory that, in the right hemisphere, semantic memories are represented within a distributed system, on the basis of semantic features, whereas, in the left hemisphere representations are, as in local models, relatively more holistic, and are connected via associative links.

Adolescent↗

PubMed1997

Do individuals with Williams syndrome have bizarre semantics? Evidence for lexical organization using an on-line task.

Williams syndrome, a neurodevelopmental disorder, has attracted a great deal of debate concerning the purported intactness of language in the face of other serious cognitive deficits. As more in-depth studies of specific aspects of WS language have emerged, the notion of a preserved language module has been seriously challenged. Although WS vocabulary scores are often impressive, several investigators have claimed the WS semantics are aberrant. All studies hitherto have been based on off-line experiments which necessarily involve metalinguistic processes. This clearly affects the performance of individuals with cognitive deficits. We report here an on-line study probing the semantic structure of the WS lexicon, using a task-semantic priming-which minimises metalinguistic demands. We show that WS subjects display the same taxonomic/category and thematic/functional priming effects as normal controls. The results are discussed in terms of the differences between receptive and expressive language, as well as the fact that although semantic memory and the automatic access to semantic information for individual words is normal in WS, the integration of semantic information into sentence comprehension may be abnormal. The importance of online tasks to highlight such differences is stressed.

Adolescent↗

PubMed2006

Semantic knowledge in mild cognitive impairment and mild Alzheimer's disease.

The aim of this study was to investigate memory in patients with mild cognitive impairment (MCI) and mild Alzheimer's disease (AD). Ten patients with MCI, 11 with AD and a group of age and education matched healthy control participants were assessed on a comprehensive battery of semantic memory tests, including traditional semantic memory measures and a non-verbal test of knowledge of object use. The MCI group was impaired on tests of category fluency and all three conditions of an object knowledge test (matching to recipient, function and action), plus a difficult object-naming test. The mild AD group showed additional impairments on traditional measures of semantic memory, including naming high frequency items, comprehension and semantic association. Together these findings suggest that semantic memory impairments occur early in the course of AD, more specifically in patients with "amnesic" MCI, and provide further evidence that impaired category fluency reflects semantic breakdown.

Adult↗

PubMedDate not supplied

Two further investigations of autobiographical memory in semantic dementia.

A number of investigations in semantic dementia have documented better retrieval of recent personal events compared to those in the more distant past (Graham and Hodges, 1997). Westmacott et al. (2001) challenged this result, however, finding relative preservation of remote memories in a single case of semantic dementia when he was tested using family photographs. In Experiment 1, we tested two possible explanations for the discrepancy between the published papers: (a) that there is a significant effect of modality in autobiographical retrieval in semantic dementia (e.g., patients will show better, or even preserved, remote memory when tested on nonverbal, compared to verbal, tasks); and (b) that the distinct pattern seen between patients is attributable to the different methods adopted for scoring the episodic quality of the memories. A patient with semantic dementia, AM, produced autobiographical memories to both words and family photographs. These personal events were scored by two raters using the scoring method described by Westmacott et al. (2001) and that reported by Graham and Hodges (1997). It was found that AM showed similar levels of remote memory impairment regardless of whether the cue was verbal or nonverbal. In addition, significant effects of time were revealed in AM's performance on the verbal memory test, regardless of which method was used to score the memories. In Experiment 2, we investigated a related question: whether the relatively better retrieval of memories in semantic dementia could be due to over rehearsal of highly salient recent experiences? Four patients were tested on their ability to remember a recent event (either a trip to London or events from a Formula One Grand Prix race) using specially designed autobiographical questionnaires. It was found that all four were able to perform this task, although one patient showed evidence of some forgetting over three months, and another exhibited difficulty discriminating between two similar events. Together, the two experiments further confirm that patients with semantic dementia show a modality independent autobiographical memory deficit, with better retrieval of recent events.

Aged↗

PubMed1978

"Semantic" and "acoustic" errors of aphasic and schizophrenic patients in a sound-picture matching task.

Broca's aphasics, Wernicke's aphasics, brain-damaged patients without aphasia, and chronic schizophrenics were tested on a task to match meaningful sounds to one of four pictures. One of the depicted objects was the natural source of the sound, one was an object belonging to the same semantic category as the correct object, one was an object producing acoustically similar sounds as the correct object, and one was an object not related either semantically or acoustically to the correct object. In one item set the "semantic" distractors produced a sound completely different from the presented one; in another item set the "semantic" distractors made practically no specific sounds at all. Broca's and Wernicke's aphasics were shown to have significantly higher total error scores than brain-damaged patients without aphasia and to make significantly more "semantic" errors only on the first item set and "acoustic" errors on both item sets than the brain-damaged patients without aphasia. However, after correcting for guessing the differences between groups with respect to "semantic" and "acoustic" errors vanished. The aphasics' difficulties in coping with the sound-picture matching task might be difficulties in processing the acoustic dimensions of the items. It is, however, suggested that the impairment is not perceptual but of the cognitive kind repeatedly demonstrated in tasks which require the analytic extraction of features of the stimulus or of the concept represented by the stimulus.

Aphasia↗

PubMed2001

The impact of semantic impairment on word stem completion in Alzheimer's disease.

Both the extent of semantic memory impairment and the level of processing attained during encoding might constitute critical factors in determining the amount of word-stem completion (WSC) priming encountered in Alzheimer's disease (AD) subjects. We investigated the impact of varying encoding level in AD and elderly normal subjects, using a set of stimuli ranked as "intact" or "degraded" in terms of each subject's semantic knowledge on probe questions. For both shallow and deep encoding conditions, overall priming in the two subject groups was equivalent. However, for the deep encoding condition, consisting of a semantic judgment task performed on each target word, the priming effect noted in AD subjects was significantly smaller for semantically degraded items than for semantically intact items. Results indicate that the degree of semantic impairment represents one important variable affecting the amount of WSC priming which results when deep encoding procedures are used at study.

Aged↗

PubMed2001

Exploration of hemispheric specialization and lexico-semantic processing in unilateral temporal lobe epilepsy with verbal fluency tasks.

Verbal production has been shown to rely on both hemispheres differentially. To determine how lateralized brain lesions affect the generation of isolated words, we evaluated three subject groups: normal controls (n=22), and patients with right (n=23), and left (n=22) non-operated temporal lobe epilepsy (TLE) using three verbal fluency tasks (letter, phonetic, semantic). LTLE patients produced fewer words than controls in the phonetic, letter, semantic conditions, whereas RTLE patients were only impaired in the semantic task. Hence, there would be a hemispheric specialization in language where phonetic processing involves mostly the left temporal lobe and semantic aspects of production involve both temporal lobes. And, in order to study disruption of semantic lexicon involved in supermarket fluency (to name things which can be bought in a supermarket), specific indicators Tröster et al., (1998) [Tröster AI, Fields JA, Testa JA, Paul RH, Blanco CR, Hames KA, Salmon DP, Beatty WW. Cortical and subcortical influences on clustering and switching in the performance of verbal fluency Tasks, Neuropsychologia 1998;36:295-304.] were exploited. Our results indicated that TLE groups made fewer category shifts than controls. Also, RTLE patients used labels more frequently and produced fewer exemplars. Results show the specificity of processing according to cue, and suggest that the semantic fluency deficits due to TLE be primarily due to an alteration of the mental lexicon.

Adult↗

PubMed1997

Influence of perceptual and semantic conflicts between the two halves of chimeric stimuli on the expression of visuo-spatial neglect.

We investigated how perceptual and semantic relationships between the left and right half of chimeric stimuli influence overt and covert visual processing by asking eight right brain damaged (RBD) patients with hemispatial neglect to identify complete, half-, and chimeric drawings. Chimeric stimuli belonged in one of four categories defined according to the perceptual and semantic relatedness between the two compounding hemi-figures. Thus, the hemi-figures could be related both perceptually and semantically, only perceptually, only semantically, or neither perceptually nor semantically. Although patients often appeared to base their report on the right part of the chimerics, the number of errors was minimal when conflicts between the two hemi-figures were maximal. Moreover, perceptual conflicts, which mainly affect the perception of the shape, appeared to influence the performance more than semantic conflicts. Since the analysis of shape incongruency is probably accomplished at early levels of information processing, the result suggests that preattentive analysis is largely spared in the experimental patients and that, in our task, bottom-up factors more than top-down factors modulate the expression of left neglect.

Aged↗

PubMed1998

Naming in semantic dementia--what matters?

One of the major symptoms of semantic dementia (or progressive fluent aphasia) is profound word-finding difficulties. We present here a cross-sectional study of the factors affecting picture naming in semantic dementia based on data obtained from eight patients, together with a longitudinal analysis of naming in another patient. Various properties and attributes of the objects were entered into a series of regression analyses in order to predict which items the patients could or could not name. The analyses showed that object familiarity, word frequency and age-of-acquisition predicted naming success for the group and, in most cases, for each individual patient, irrespective of lesion site or overall naming success. We propose that the pattern of naming in semantic dementia is best described in terms of reduced semantic activation within a cascading/interactive speech production system. We suggest that object familiarity, and possibly word frequency, reflect the inherent robustness of individual semantic representations to the decay process in terms of both quantity and quality of experience. Age-of-acquisition and word frequency (at a phonological-lexical level) predicts naming success, because frequent, early-acquired words are relatively easy to activate even with reduced semantic "input".

Adult↗

PubMed1998

Going, going, gone...? Implicit and explicit test of conceptual knowledge in a longitudinal study of semantic dementia.

Patients suffering from semantic dementia provide important constraints on theories of the structure and organisation of semantic memory. In this article we report one such patient, AM, whose progressive deterioration of semantics enables us to address the much-debated issue of whether conceptual structure is hierarchically organised. The hierarchical account predicts that brain damage should impair lower levels of the hierarchy (property information) before affecting higher level (category) information (Warrington and Shallice, Q. J. Exp. Psychol. 1975, 27, 635-657). We evaluate this prediction by repeated testing of AM in two studies--a semantic priming task and a verification task--over an 18 month period, contrasting the progressive deterioration of properties (functional and perceptual) and category relations (category co-ordinates and category labels). Properties were preserved longer than category information, arguing against a hierarchical account of semantic memory. In addition, functional properties were most robust to brain damage, supporting our claim that functional information plays a special role in semantic representations (Durrant-Peatfield et al., Proc. 19th Ann. Conf. of the Cognitive Science Society. Erlbaum, Mahwah, NJ, 1997. pp. 193-198. Tyler et al., Cognitive Neuropsychol. 1997, 14, 511-545).

Anomia↗

PubMed2006

[Automatic recall of didactic knowledge in semantic memory during normal aging and in Alzheimer's disease].

INTRODUCTION: The goal of our work is to study the most consolidated items of semantic memory in normal subjects and in patients with Alzheimer's disease (AD). PATIENTS AND METHOD: The first test is based on automatic recall of didactic knowledge. This test is made of 250 automatic verbal expressions exploring general knowledge. It as been validated according to age and cultural levels in 219 normal subjects (20-90 years old). Another simplified test called EVA including only 50 of the 250 previously chosen items was also used. The EVA scores found in a normal population have been classified by centilages according to age and cultural levels. The EVA was also tested in 20 patients with AD and the results compared with MMSE and "Pyramids and Palm Trees Test" (semantic memory testing). RESULTS: The results reveal that the scores observed with the first test in a normal population with comparable cultural levels are correlated with age. EVA test scores found in control subjects show that the median value, for a same age group, is positively correlated with cultural levels. In patients with AD, scores for EVA test and MMSE are associated, the low results being linked to the severity of dementia. In addition, scores for EVA test and "Pyramids and Palm Trees Test" are also significantly correlated. Seven patients with mild dementia (MMSE>20) have abnormal scores for the "Pyramids and Palm Trees Test". CONCLUSION: Our study confirms that changes linked to aging do not involve all aspects of cognition. The most consolidated items of semantic memory assessed by EVA test seem to resist at the beginning of AD but later decline similarly to the other items of semantic memory. Normal results for EVA tests do not imply that semantic memory is not affected in the early phases of AD. We propose this new test which assesses the semantic memory stock without involving an active process of recuperation. This test is not suitable for an early diagnosis of AD but could help to evaluate the severity of the disease during the evolution.

Adult↗

PubMed1998

Semantic priming in major depressive state.

We studied semantic priming in 20 major depressive subjects. The methodology used was a visual lexical decision task. Semantic priming is the facilitation of target word recognition (shortening of response time) by the prior presentation of a semantically related context (a prime word). It relies on semantic processing of words and context, facilitating early cognitive stages of response. Varying the temporal interval between prime and target words onset allows us to distinguish between two priming mechanisms, relying on more automatic (test 1) or more controlled (i.e. attention dependent) (test 2) information processing. We observe a significant retardation for words and pseudo-words in depressives (in relation to controls) in both tests. In spite of a general retardation and increase of response times in depressives, semantic priming is evident in both groups and both tests, and does not differ significantly between depressive and control groups in either automatic or controlled conditions. Theses results confirm that semantic processing is not impaired in depression, and are discussed with regard to the hypothesis of an effortful processing impairment in depression, and to depressive retardation.

Adult↗