A single-system account of semantic and lexical deficits in five semantic dementia patients

In semantic dementia (SD), there is a correlation between performance on semantic tasks such as picture naming and lexical tasks such as reading aloud. However, there have been a few case reports of patients with spared reading despite profound semantic impairment. These reports have sparked an ongoing debate about how the brain processes conceptual versus lexical knowledge. One possibility is that there are two functionally distinct systems in the brain—one for semantic and one for lexical processing. Alternatively, there may be a single system involved in both. We present a computational investigation of the role of individual differences in explaining the relationship between naming and reading performance in five SD patients, among whom there are cases of both association and dissociation of deficits. We used a connectionist model where information from different modalities feeds into a single integrative layer. Our simulations successfully produced the overall relationship between reading and naming seen in SD and provided multiple fits for both association and dissociation data, suggesting that a single, cross-modal, integrative system is sufficient for both semantic and lexical tasks and that individual differences among patients are essential in accounting for variability in performance.     

A single-system account of semantic and lexical deficits in five semantic dementia patients

In semantic dementia (SD), there is a correlation between performance on semantic tasks such as picture naming and lexical tasks such as reading aloud. However, there have been a few case reports of patients with spared reading despite profound semantic impairment. These reports have sparked an ongoing debate about how the brain processes conceptual versus lexical knowledge. One possibility is that there are two functionally distinct systems in the brain-one for semantic and one for lexical processing. Alternatively, there may be a single system involved in both. We present a computational investigation of the role of individual differences in explaining the relationship between naming and reading performance in five SD patients, among whom there are cases of both association and dissociation of deficits. We used a connectionist model where information from different modalities feeds into a single integrative layer. Our simulations successfully produced the overall relationship between reading and naming seen in SD and provided multiple fits for both association and dissociation data, suggesting that a single, cross-modal, integrative system is sufficient for both semantic and lexical tasks and that individual differences among patients are essential in accounting for variability in performance.     

Heterogeneity of semantic and visuospatial deficits in early Alzheimer's disease

Staging of visuospatial and semantic deficits in patients with dementia of the Alzheimer type (DAT) was examined. The authors hypothesized that semantic ability would be more impaired in these patients, reflecting predominant temporal pathology early in the disease. However, in the 1st study (n = 26), 3 patients (11.5%) had marked visual but no semantic impairment. This finding was extended in a 2nd study with a 2nd patient sample (n = 21) and more specific tasks. Two patients (9.5%) again had visual but no semantic impairment. These studies confirm that, in patients with DAT presenting with relatively focal deficits, visual deficits sometimes occur before semantic problems. The findings are discussed with regard to the cognitive demands and neuroanatomical underpinning of the tests used and point to the necessity of using cognitively specific tests to enable accurate analysis of deficits in the context of the neuroanatomical basis of impairment.     

New directions in the study of semantic deficits: a comment on Storms et al. (2003)

G. Storms, T. Dirikx, J. Saerens, S. Verstaeten, and P. P. De Deyn (2003) have provided an important critique of the use of multidimensional scaling (MDS) to evaluate semantic knowledge in Alzheimer's disease. If MDS is to be used with semantic proximity data (in spite of well-documented reasons for not doing so), at minimum, the issues raised in G. Storms et al. should be considered. A few criticisms of the target article are presented. Then, the manner in which key points from the article, along with a consideration of such factors affecting proximity elicitation as semantic domains, tasks, and the experimental context, could be applied to correct certain shortcomings in the literature are discussed.     

Disparate letter and semantic category fluency deficits in autopsy-confirmed frontotemporal dementia and Alzheimer's disease

Patients with autopsy-confirmed frontotemporal dementia (FTD; n = 16) and Alzheimer's disease (AD; n = 32) were compared on first-letter and semantic category fluency tasks. Despite being matched on age, education, and dementia severity, FTD patients performed worse overall and showed similar impairment in letter and semantic category fluency, whereas AD patients showed greater impairment in semantic category than letter fluency. A measure of the disparity between letter and semantic category fluency (the semantic index) was effective in differentiating FTD from AD patients, and this disparity increased with increasing severity of dementia. These unique patterns of letter and semantic category fluency deficits may be indicative of differences in the relative contribution of frontal-lobe-mediated retrieval deficits and temporal-lobe-mediated semantic deficits in FTD and AD.     

What are the causes of reduced fit in scaling and clustering studies of semantic proximity data,and how else to measure them: a comment on Storms et al. (2003)

G. Storms, T. Dirikx, J. Saerens, S. Verstraeten, and P. P. De Deyn (2003) noted that the goodness-of-fit indices for scaling and clustering solutions of proximity data from populations with hypothesized semantic deficits tend to be reduced in comparison with control participants, and that this precludes an unambiguous interpretation of such data. However, this effect is not necessarily as inconsistent with the proposal of semantic degradation in these groups, or as consistent with explanations in terms of access or attentional problems, as is suggested by G. Storms et al. Also, although performance on word fluency tasks is certainly constrained by the ability to access stored information, there are ways in which this confounding influence may be controlled for in the study of semantic deficits.     

Simplified use of the semantic differential to measure psychotherapy outcome

To initially establish the validity and utility of a simplified use of the Semantic Differential to measure psychotherapy outcome, 14 clients were administered, before and after 15 sessions of individual psychotherapy, the Semantic Differential and a symptom checklist. As predicted, results indicated that change of clients' self-constructs in a positive direction was associated with symptom reduction. Implications for psychotherapy research are discussed.     

Altered navigational strategy use and visuospatial deficits in hAPP transgenic mice

Navigation deficits are prominent in Alzheimer's disease (AD) patients and transgenic mice expressing familial AD-mutant hAPP and A beta peptides. To determine the impact of strategy use on these deficits, we assessed hAPP and nontransgenic mice in a cross maze that can be solved by allocentric (world-based) or egocentric (self-based) strategies. Most nontransgenic mice used allocentric strategies, whereas half of hAPP mice were egocentric. At 3 months, all mice learned the cross maze rapidly; at 6 months, only allocentric hAPP mice were impaired. At 3 and 6 months, hAPP mice had reduced hippocampal Fos expression, which correlated with cross maze learning in older mice. Striatal pCREB expression was unaltered in hAPP mice, suggesting striatal sparing. We conclude that egocentric strategy use may be an earlier indicator of hAPP/A beta-induced hippocampal impairment than spatial learning deficits. Persistent use of allocentric strategies when egocentric strategies are available is maladaptive when there is hippocampal damage. Interventions promoting flexibility in selecting learning strategies might help circumvent otherwise debilitating navigational deficits caused by AD-related hippocampal dysfunction.     

On the motivational deficits after medial hypothalamic lesions

After medial hypothalamic (MH) lesions, rats overeat when given free access to food and undereat when given limited access to food. The present experiments, designed to ascertain the specificity of appetite dysfunctions after MH lesions, indicated: (1) that rats with MH lesions, which do not adjust food intake appropriately during food deprivation, do drink normally when water deprived; (2) that the motivational deficit is apparent in instrumental situations using variable-interval and continuously reinforced schedules of reinforcement; and, (3) that rats with bilateral lateral hypothalamic (LH) lesions respond to food deprivation in a fashion similar to normal rats. These data support the idea that a discrete mechanism which controls the energization of feeding associated instrumental behaviors after food deprivation resides in the medial hypothalamus.     

On the roles of distinctiveness and semantic expectancies in episodic encoding of emotional words

We examined the factors that contribute to enhanced recall for emotionally arousing words by analyzing behavioral performance, the P300 as an index of distinctiveness, and the N400 as an index of semantic expectancy violation in a modified Von Restorff paradigm. While their EEG was recorded, participants studied three list types (1) neutral words including one emotionally arousing isolate (either positive or negative), (2) arousing, negative words including one neutral isolate, or (3) arousing, positive words including one neutral isolate. Immediately after each list, free recall was tested. Negative, but not positive, words exhibited enhanced recall when presented as isolates in lists of neutral words and elicited a larger P300 for subsequently recalled than not‐recalled words. This suggests that arousing, negative words stand out and that their distinctiveness contributes to their superior recall. Positive valence had an enhancing effect on recall only when the list contained mostly other positive words. Neutral isolates placed in either positive or negative lists elicited an N400, suggesting that semantic expectations developed in emotional word lists regardless of valence. However, semantic relatedness appeared to more strongly contribute to recall for positive than negative words. Our results suggest that distinctiveness and semantic relatedness contribute to episodic encoding of arousing words, but the impact of each factor depends on both a word's valence and its context.     

Event-related brain potential study of expectancy and semantic matching in schizotypy

Priming studies have revealed semantic processing abnormalities in subjects that display high schizotypal traits. The objective of the present study was to further elucidate the contribution of predictive (expectancy) and integrative (semantic matching) context processing to the semantic deficit described in schizotypy. Thirty-six participants were assigned into high or low schizotypy groups according to their score on the Schizotypal Personality Questionnaire (SPQ), and event-related brain potentials were recorded while these individuals performed semantic judgments based on asymmetrically associated word pairs. Viewed in one direction (forward), the target was highly predictable from the prime, whereas in the backward direction, the prime-to-target association was weak. It was assumed that the forward condition would be dependent on expectancy generation, while the backward condition would rely on semantic matching. In the low-SPQ group, forward and backward related words evoked a reduced (less negative) N400 amplitude compared to unrelated words, resulting in a significant forward and backward N400 priming effect, respectively. By contrast, only forward related words were facilitated in the high-SPQ group, resulting in significant forward priming and a lack of backward priming. Furthermore, the N400 amplitude for forward related words was less negative within the high-SPQ group in comparison to the low-SPQ group, which indicated easier semantic access to predictable words for high-SPQ individuals. Therefore, schizotypy may be associated with an imbalance in the use of predictive and integrative context processing strategies, namely preserved, if not overallocated, expectancy generation along with altered integration of unpredictable words due to semantic matching deficit.     

The "living things" impairment and the nature of semantic memory organisation: An experimental study using PI-release and semantic cues

The present paper evaluated categorical and featural proposals of memory organisation, for explaining the living/nonliving things dissociation observed in semantic memory. The experimental study used the Release from Proactive Interference (PI-release) paradigm. Normal subjects were tested with this task using word vs. picture stimuli in a standard taxonomical PI-release condition (i.e., nonliving to living things) and in a cue condition with attributes that run opposite to the taxonomical shift. Experiments 1 and 2 cued functional attributes (means of transportation; dangerousness), and experiments 3 and 4 cued perceptual attributes (size; number of legs). The overall pattern of PI-release emphasizes the role of functional attributes and the role of structural processing to semantic processing. Implications for the different proposals presented, including possible alternative accounts of the results, are also discussed.     

Brain activity during syntactic and semantic processing--a magnetoencephalographic study

Drawings of objects were presented in series of 54 each to 14 German speaking subjects with the tasks to indicate by button presses a) whether the grammatical gender of an object name was masculine ("der") or feminine ("die") and b) whether the depicted object was man-made or nature-made. The magnetoencephalogram (MEG) was recorded with a whole-head neuromagnetometer and task-specific patterns of brain activity were determined in the source space (Minimum Norm Estimates, MNE). A left-temporal focus of activity 150-275 ms after stimulus onset in the gender decision compared to the semantic classification task was discussed as indicating the retrieval of syntactic information, while a more expanded left hemispheric activity in the gender relative to the semantic task 300-625 ms after stimulus onset was discussed as indicating phonological encoding. A predominance of activity in the semantic task was observed over right fronto-central region 150-225 ms after stimulus-onset, suggesting that semantic and syntactic processes are prominent in this stage of lexical selection.     

Familial clustering in burnout: a twin-family study

BACKGROUND: Research on risk factors for burnout has mainly focused on circumstances at work and on personal characteristics. The aim of this study was to investigate whether burnout clusters within families and, if so, whether this is due to genetic influences or to environmental factors shared by family members. Finally, we tried to identify specific risk factors for burnout. METHOD: In 2707 twins, 736 of their siblings and 575 of their spouses from a population-based twin-family sample, burnout was measured using a self-report questionnaire. Correlations in burnout scores were obtained for monozygotic and dizygotic twin pairs and sibling pairs conditional on the pairs' sex. Correlations for twins and their spouses were derived conditional on the length of the relationship. RESULTS: In the final model, correlations of the monozygotic and dizygotic twin pairs and sibling pairs were significantly different from zero, but not significantly different from each other. The correlation was estimated at 0.22. The correlation between spouses was also significant. This was mainly due to the group with a relationship longer than 5 years in which the correlation was 0.24. Burnout scores were higher in subjects whose parents had a high level of education. CONCLUSIONS: There is familial clustering for burnout due to environmental factors shared by family members, explaining 22 % of the variance. Genetic factors do not seem to be of importance. The significant correlation between spouses supports the conclusion that common environment plays a role in burnout. A high parental education is one of the familial risk factors.     

Analysis of the semantic representations of living and nonliving concepts: A normative study

Current feature-based semantic memory models assume that the semantic representations of concepts differ systematically across living and nonliving categories and that such differences account for the emergence of category-specific semantic deficits in brain-damaged people. To assess some of the different models' main assumptions about structural differences at the semantic feature level in the two major semantic domains, we administrated a feature-listing task to normal young volunteers on 64 concepts drawn from living and nonliving semantic categories. We investigated whether feature correlation, a variable with a crucial role in the emergence of category-specific deficits, should be computed as a concept-dependent or as a concept-independent measure, and we chose the former. We also addressed the issue of a psychological counterpart of feature production frequency. Finally, we analysed the database obtained from the feature-listing tasks, looked at cross-domain differences for correlation, feature frequency, distinctiveness, and feature type, and discussed the implications of these findings for current semantic memory models.     

Analysis of the semantic representations of living and nonliving concepts: A normative study

Current feature-based semantic memory models assume that the semantic representations of concepts differ systematically across living and nonliving categories and that such differences account for the emergence of category-specific semantic deficits in brain-damaged people. To assess some of the different models' main assumptions about structural differences at the semantic feature level in the two major semantic domains, we administrated a feature-listing task to normal young volunteers on 64 concepts drawn from living and nonliving semantic categories. We investigated whether feature correlation, a variable with a crucial role in the emergence of category-specific deficits, should be computed as a concept-dependent or as a concept-independent measure, and we chose the former. We also addressed the issue of a psychological counterpart of feature production frequency. Finally, we analysed the database obtained from the feature-listing tasks, looked at cross-domain differences for correlation, feature frequency, distinctiveness, and feature type, and discussed the implications of these findings for current semantic memory models.