Category fluency is also predominantly affected in Swiss Alzheimer's disease patients

Objectives – To establish the comparative efficacy to differentiate between Swiss patients with dementia of the Alzheimer type (DAT) and elderly normal control subjects (NC) on two different verbal fluency tasks: category fluency and letter fluency. Material and methods – Fifty Swiss German DAT patients in the early stages of the disease and 50 matched normal control subjects were compared on letter and category fluency tasks. Results – DAT patients exhibited an overproportional impairment on category fluency as compared with letter fluency. Receiver operating characteristic curves (ROC) showed that category fluency correctly classified a significantly higher number of DAT patients and NC subjects (84%) than letter fluency (70%). Conclusion – As similar findings have been described for English-speaking DAT patients, we conclude that deficiencies in category fluency are a general phenomenon, reflecting impaired structures of semantic knowledge occurring early in the course of Alzheimer's disease.     

Word retrieval to letter and semantic cues: A double dissociation in normal subjects using interference tasks

Recent evidence suggests that letter and semantic category verbal fluency tasks may use different component processes of a distributed word retrieval system. We hypothesized that the retrieval of words that begin with the same letter places greater demands on frontal lobe mediated strategic search processes than on temporal lobe mediated semantic knowledge. Conversely, generation of words from the same semantic category places greater demands on semantic knowledge than on strategic search. This hypothesis was tested by requiring subjects to generate lists of words to letter and semantic cues alone and while performing an interference task. A motor sequencing task (developed by Moscovitch, Neuropsychology of Memory, pp. 5–22, 1992) was used to activate frontal regions and an object decision task was used to activate posterior temporal cortex. In support of the hypothesis, letter fluency was reduced to a greater extent by concurrent performance of the motor sequencing task than by the object decision task. The opposite interference pattern was found for semantic category fluency.     

Patterns of Word-List Generation in Mild Cognitive Impairment and Alzheimer's Disease

Patients with amnestic mild cognitive impairment (aMCI) have been described as exhibiting greater impairment on tests of category fluency than letter fluency. This has been offered as evidence that this condition represents pre-clinical Alzheimer's disease (AD). We hypothesized that this pattern of differential impairment is dependent on the specific semantic categories and initial letters selected, and is not specific to AD and aMCI. A total of 40 cognitively normal older adults, 74 MCI patients—25 “amnestic single domain” (aMCI), 27 “amnestic multiple domain”, and 22 non-amnestic—and 29 AD patients were tested with multiple forms of semantic-category and initial-letter fluency tasks. The pattern of deficits within and across groups was highly dependent on the specific categories and letters chosen. Overall, aMCI patients did not demonstrate greater impairment in category than letter fluency. In fact, the level and pattern of their performance resembled that of cognitively normal older adults much more than AD patients. MCI patients with deficits in multiple cognitive domains performed most like AD patients. These findings indicate that verbal fluency performance is highly influenced by the specific tasks used, and impairment on semantic fluency is not characteristic of pure amnestic MCI.     

Verbal fluency in Parkinson’s disease patients on/off dopamine medication

IntroductionParkinson’s disease (PD) is associated with dopamine depletion in the fronto-striatal network which affects some language aspects such as verb processing. Some experiments have demonstrated that dopamine deficiency plays a role in the normal functioning of the lexico-semantic system. As a result, the verbal fluency task could be a useful tool to assess the function of the semantic system, by examining both the number of words generated and the frequency of use of those words.ObjectiveThe aim of this study was to find out how dopamine affects the performance of PD patients using a verbal fluency task, focussing on action-word fluency.MethodA group of 20 PD patients and 20 controls participated in the study. Participants were assessed with four different verbal fluency tasks: phonological, semantic (animal and supermarket words) and action fluency. PD patients were tested twice (on/off medication) and controls only once.ResultsFor the number of words, there were significant differences between PD patients on and off medication in the phonological and action fluency tasks. Compared to controls, PD off medication produced significantly fewer words in phonological, and actions. Regarding frequency, differences were found between PD patients off medication and controls for the action-word category.DiscussionOur data showed a specific deficit in PD patients off medication in categories mainly depending on frontal lobe function (phonological and actions) while these differences were restored with dopamine treatment. Moreover, PD patients off medication produced higher frequency verbs than controls, suggesting that dopamine affects the normal functioning within the lexico-semantic network of verbs.     

Cut the coda: early fluency intervals predict diagnoses

The aim of this study was threefold: (i) to clarify whether letter and category fluency tap different cognitive abilities; (ii) to make diagnostic comparisons and predictions using temporally resolved fluency data; (iii) to challenge and test the widely made assumption that 1-min sum scores are the fluency test measure of choice in the diagnosis of dementia. Scores from six 10-sec intervals of letter and category fluency tests were obtained from 240 participants including cognitive levels ranging from mild subjective cognitive complaints to Alzheimer's disease. Factor analysis revealed clearly separate factors corresponding to letter and category fluency. Category fluency was markedly impaired in Alzheimer's disease but not in Mild Cognitive Impairment. Only scores from relatively early intervals predicted Alzheimer's disease and Mild Cognitive Impairment. The conclusions are (i) letter and category fluency are different tests, category fluency being the best diagnostic predictor; (ii) it would be possible to administer category fluency tests only for 30 sec, because after this point the necessary differential diagnostic information about the patient's word fluency capacity has already been gathered.     

Diagnostic utility of letter fluency, category fluency, and fluency difference scores in Alzheimer's disease

Word generation tasks, specifically letter fluency and category fluency, are a standard part of most test protocols used by clinical neuropsychologists to measure aspects of language and executive retrieval functions. Given the reliance on these measures as clinical tools, it is important to understand the diagnostic implications of patients' performances. In Alzheimer's disease (AD), category fluency has generally been found to be disproportionately impaired, whereas letter fluency is usually more mildly impaired. It has been proposed that this performance pattern occurs because access to temporal-lobe semantic stores is necessary for category fluency but not letter fluency. In this study, the diagnostic utility of category fluency, letter fluency, and difference scores (letter fluency minus category fluency) in AD were examined. Forty AD patients and 221 normal control subjects took category fluency and letter fluency tests. Traditional t-test comparisons revealed that the groups differed significantly on the two test tasks and in terms of mean difference scores. However, using sensitivity and specificity to calculate predictive values, only category fluency and letter fluency (but not difference scores) were useful in predicting AD in individuals. Furthermore, category fluency was superior to letter fluency in this regard. Likelihood ratio tables are provided for use in calculating the odds of AD for specific category fluency and letter fluency scores generated by individual patients.     

Diagnostic Utility of Letter Fluency,Category Fluency,and Fluency Difference Scores in Alzheimer's Disease

Word generation tasks, specifically letter fluency and category fluency, are a standard part of most test protocols used by clinical neuropsychologists to measure aspects of language and executive retrieval functions. Given the reliance on these measures as clinical tools, it is important to understand the diagnostic implications of patients' performances. In Alzheimer's disease (AD), category fluency has generally been found to be disproportionately impaired, whereas letter fluency is usually more mildly impaired. It has been proposed that this performance pattern occurs because access to temporal-lobe semantic stores is necessary for category fluency but not letter fluency. In this study, the diagnostic utility of category fluency, letter fluency, and difference scores (letter fluency minus category fluency) in AD were examined. Forty AD patients and 221 normal control subjects took category fluency and letter fluency tests. Traditional t -test comparisons revealed that the groups differed significantly on the two test tasks and in terms of mean difference scores. However, using sensitivity and specificity to calculate predictive values, only category fluency and letter fluency (but not difference scores) were useful in predicting AD in individuals. Furthermore, category fluency was superior to letter fluency in this regard. Likelihood ratio tables are provided for use in calculating the odds of AD for specific category fluency and letter fluency scores generated by individual patients.     

Initial letter and semantic category fluency in Alzheimer''s disease, Huntington''s disease, and progressive supranuclear palsy.

Ten patients with dementia of Alzheimer's type, 10 patients with progressive supranuclear palsy, and 10 patients with Huntington's disease were compared on two types of verbal fluency task--namely, initial letter fluency and category (semantic) fluency. The groups were carefully matched for overall level of dementia on the dementia rating scale, and were compared with 25 age matched normal controls. The controls found letter fluency more difficult than category fluency, and this relative pattern of performance was repeated in the progressive supranuclear palsy and Huntington's disease groups, although both groups were significantly impaired on both tasks. By contrast, patients with Alzheimer's disease performed just as poorly as the progressive supranuclear palsy and Huntington's disease groups on the category tasks, but were significantly less impaired at letter fluency, performing at near normal levels on this task. From these results, it is suggested that the performances of patients with progressive supranuclear palsy and Huntington's disease relate largely to initiation and retrieval problems secondary to disruption of frontostriatal circuits, whereas in Alzheimer's disease, the poorer performance on category fluency is due principally to the breakdown of semantic knowledge, which probably reflects temporal neocortical involvement.     

Double dissociation of letter and category fluency following left frontal and temporal lobe lesions

Background: A number of studies have suggested that temporal cortex is critical for the ability to generate exemplars belonging to a particular semantic category (i.e., category fluency), while frontal cortex is critical for generating words beginning with a particular letter (i.e., letter or phonemic fluency). However, previous studies have often focused on relative, quantitative differences in performance across groups of patients and primarily in the oral domain.

Aims: The current study analysed verbal fluency data from two individuals with chronic aphasia, one with a large left temporal lobe lesion and a severe Wernicke's aphasia, and a second individual with a large left frontal lobe lesion and a moderately severe non-fluent aphasia. The goal of the study was to do both qualitative and quantitative analyses of letter and category fluency performance in these two individuals across oral and written fluency domains.

Methods & Procedures: Participants were administered both oral and written versions of letter fluency (FAS) and category fluency conditions (fruits, animals, and supermarket items). Participants were given 90 seconds to generate as many items as possible, and their responses were scored for both overall output, as well as qualitative structure using a clustering analysis.

Outcomes & Results: The individual with an extensive temporal lobe lesion generated a large number of exemplars on the letter fluency task. Some of these items were neologisms (e.g., frest, anth, and swink), but remarkably all adhered to the phonological constraints of the task. However, this individual was very poor at generating items belonging to semantic categories. In contrast, the individual with a large frontal lesion generated many exemplars on the category fluency task but only two items on the letter fluency task. The same pattern was replicated in the written domain in both individuals, and results from the clustering analysis paralleled these quantitative findings.

Conclusions: This report describes two individuals with aphasia who exhibited a double dissociation between letter and category fluency performance in both oral and written domains. The current findings provide further evidence for the notion that left frontal cortex is critical for word retrieval based on phonology, while left temporal cortex is critical for word retrieval based on semantics. The findings have implications for the types of strategies that may be most effective in individuals with lesions to these brain regions critical for word retrieval.     

Disproportionate impairment in semantic verbal fluency in schizophrenia: differential deficit in clustering

The purpose of the current study was to investigate whether patients with schizophrenia present disproportionate impairment in semantic, relative to phonemic, fluency. Specifically, we explored whether this impairment could be explained by differential deficits in clustering or switching strategies. The Greek Verbal Fluency Test was administered to 119 patients with schizophrenia and 150 age-, education-, and gender-matched healthy controls. We calculated the total number of words generated, the number of cluster related words, and the number of switches on the semantic and phonological fluency tasks separately. Patients with schizophrenia generated fewer total words, cluster related words and switches than healthy controls on both fluency tasks. When controlling for the total number of words produced, however, the differences between the two groups in the number of cluster related words and switches disappeared. We found a disproportionate impairment in semantic, compared with phonemic, fluency in schizophrenia for total word production and the number of cluster related words, but not for the number of switches. In conclusion, patients with schizophrenia used the same strategies as healthy controls to perform on a word fluency test, but they used them less effectively. Disproportionate impairment in semantic fluency in schizophrenia resulted from a differential deficit only in clustering. Therefore, disproportionately impaired category fluency in schizophrenia may be primarily due to disorganization and not to inefficient access to and retrieval from semantic store.     

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 Tr?ster et al., (1998) [Tr?ster 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.     

Clustering strategies on tasks of verbal fluency in Parkinson's disease.

The verbal output of patients with Parkinson's disease (PD) was analyzed for semantic and phonemic clusters on tasks of verbal fluency. One task required cued retrieval by semantic category (i.e. animals), and one required non-cued retrieval by initial letter (e.g. words beginning with 'F'). Nondemented PD patients (N = 25) produced significantly fewer words on the cued semantic retrieval task than age-, gender- and education-matched normal control subjects (N = 22), but were not impaired on the non-cued letter retrieval task. However, overall, PD patients were able to form more semantic clusters than phonemic clusters. These results are discussed in light of other studies of verbal fluency deficits in patients with PD.     

Qualitative analyses of verbal fluency in adolescents and young adults with high-functioning autism spectrum disorder

Systematic qualitative analyses of verbal fluency might aid our understanding of the characteristic cognitive processes in individuals with autism spectrum disorder (ASD). In this study, we compared through qualitative and quantitative analyses performance on letter fluency (LF), category fluency (CF), and action fluency (AF) in adolescents and young adults with high-functioning autism spectrum disorders (HFASD) with that of an age-, gender-, and IQ-matched control group. Quantitative analyses revealed significantly fewer correct responses on category and action fluency and significantly more intrusions on category fluency in individuals with HFASD than in control participants. Qualitative analyses revealed significantly fewer semantic clusters and significantly more phonemic clusters during action fluency in individuals with HFASD compared to control participants. With respect to action fluency, the number of correct responses and clusters were related to verbal IQ for individuals with HFASD but not for control participants. We discuss these results in terms of abnormalities in semantic/phonemic strategy choice, cognitive flexibility, and generativity in ASD.     

Role of frontal versus temporal cortex in verbal fluency as revealed by voxel-based lesion symptom mapping.

Category and letter fluency tasks have been used to demonstrate psychological and neurological dissociations between semantic and phonological aspects of word retrieval. Some previous neuroimaging and lesion studies have suggested that category fluency (semantic-based word retrieval) is mediated primarily by temporal cortex, while letter fluency (letter-based word retrieval) is mediated primarily by frontal cortex. Other studies have suggested that both letter and category fluency are mediated by frontal cortex. We tested these hypotheses using voxel-based lesion symptom mapping (VLSM) in a group of 48 left-hemisphere stroke patients. VLSM maps revealed that category and letter fluency deficits correlate with lesions in temporal and frontal cortices, respectively. Other regions, including parietal cortex, were significantly implicated in both tasks. Our findings are therefore consistent with the hypothesis that temporal cortex subserves word retrieval constrained by semantics, whereas frontal regions are more critical for strategic word retrieval constrained by phonology.     

Phonological fluency is uniquely impaired in Japanese-speaking schizophrenia patients: confirmation study

In alphabet-based language-speaking patients with schizophrenia, category fluency is disproportionately disturbed as compared with phonological fluency. Deficits in category and phonological fluency observed in Japanese patients, however, were similar. The aim of the present study was to replicate these findings by modifying the task to minimize the influence of lack of motivation and concentration in the patients. Similar deficits were found in both types of fluency in Japanese patients. Patients who speak Japanese have deficits in phonological fluency, compared with patients who speak alphabet-based languages, suggesting that the pattern of impairment in verbal fluency in schizophrenia is dependent on the specific language system.     

Longitudinal patterns of fluency impairment in dementia: The role of domain and “nuisance variables”

Background: The potential differential impact of Alzheimer's disease (AD) across semantic categories/domains (i.e., living/nonliving) has been debated extensively in the past 30 years. An important methodological consideration in this area is the issue of whether category effects are genuine or a by-product of intrinsic properties of items, i.e., nuisance variables (NVs).

Aims: The study's aim was to investigate whether NVs versus semantic domain of words generated in a semantic fluency task better predict semantic impairment.

Methods & Procedures: We examined semantic fluency performance of demographically matched AD patients and controls. AD patients were longitudinally examined over a 2-year period. Norms of all NVs known to differ across domains were obtained for each word generated; influence of domain was also studied.

Outcomes & Results: AD patients generated fewer words than controls. However, both groups showed fairly similar performance: more familiar words, with earlier acquisition, and representing concepts with higher manipulability were generated. Domain exerted similar influence on semantic fluency performance in controls and patients at initial evaluation, but it did not influence performance as the disease advanced. In contrast, the role of familiarity increased with disease progression.

Conclusions: The role of NVs—especially familiarity—appears to be, comparatively, a more relevant predictor of longitudinal deterioration than semantic domain. Knowing which variables within a semantic fluency task longitudinally predict cognitive decline is a useful clinical tool and could possibly be a cognitive marker to improve accuracy of neuropsychological evaluation of patients with probable AD.     

Fonctions cognitives sous-jacentes aux déficits de fluence verbale dans la schizophrénie : revue de la littérature

Individuals with schizophrenia usually show impairment on various cognitive functions, including long-term memory, executive functions and language. Compared to healthy controls, their performance is impaired in verbal fluency tests. These tests require participants to generate in a given time as many words as they can, belonging to a given category (semantic fluency), or beginning with a specific letter (orthographic fluency). Various cognitive functions are involved in verbal fluency tests: psychomotor speed, executive functions, language, long-term verbal memory and semantic memory. The purpose of the present study was to clarify the functional origin of verbal fluency deficits in schizophrenia through a literature review. Nineteen articles were selected in Pubmed and PsycINFO after initial screening and detailed review. They were formally analyzed with regard to general performance, cognitive strategies used in semantic and orthographic fluency tests and, underlying cognitive origin of deficits. Results show that individuals with schizophrenia produce fewer words than healthy controls in both types of fluency tests. Their impairment is more apparent in semantic than in orthographic fluency tests. Results of studies reviewed also show that individuals with schizophrenia adopt the same clustering (i.e. production of related words within a subcategory) and switching (i.e. ability to shift between clusters when a subcategory is exhausted) strategies than healthy controls, but less efficiently. Several hypotheses, such as the impairment of executive functions, semantic memory or speed of information processing, were put forward to account for this finding. Interestingly, the few studies in which researchers performed an analysis of the semantic relationships between words produced in fluency tests showed a less semantic coherence among people with schizophrenia than in healthy controls. Such a difference could be explained by disorganization of semantic memory or impairment in the activation of conceptual representations in semantic memory. Studies in which correlations and regression analyzes were performed allow for clarifying the cognitive origin underlying verbal fluency deficits in schizophrenia. The links between these deficits and information processing speed as well as working memory are well established. These two cognitive domains also appear to be strong predictors of performance in semantic and orthographic fluency tasks in schizophrenia. Individuals with schizophrenia usually present with a significant slowdown in the speed of information processing. Such a slowdown is likely to account for their poor performance in verbal fluency tests, which require the independent and rapid production of words. Working memory disorders are also core cognitive symptoms of schizophrenia. Working memory is involved in verbal fluency tests since they involve “strategic” activation of verbal information in long-term memory, inhibition of inappropriate words, switching between clusters, etc. However, the concept of working memory also partially encompasses the notion of executive functions so that the results reported in the present literature review, according to which impairment of verbal fluency in schizophrenia results from working memory deficits but not from executive functions deficits, are difficult to interpret. Results are also less clear-cut in regard to verbal long-term memory and to language abilities. Finally, numerous studies had shown that individuals with schizophrenia present specific deficits in the organization of semantic memory. However, the impact of this deficit on verbal fluency was explored in one study only. To conclude, verbal fluency tests are sensitive to various neurocognitive conditions and are helpful for differential diagnosis. Further studies are still needed to clarify the functional origin of verbal fluency deficits in schizophrenia, in particular the differential role of executive functions and working memory as well as the impact of semantic memory impairment.     

A comparison of verbal fluency tasks in schizophrenic patients and normal controls

Previous studies have reported significant impairment on verbal fluency tasks (semantic and letter) among schizophrenic subjects. However, the possibility of specific categorical deficits has not been adequately investigated. Nor have the effects of task duration, the stability between testing sessions, and the relationship between intelligence and performance on fluency been thoroughly studied. We performed a series of 3 min fluency tasks (semantic/syntactic and letter) to determine whether duration specific or category-specific differences exist between schizophrenic subjects and normal controls. Each subject was tested at three different times as a means of estimating word pool and assessing the stability of fluency output. Subjects were asked to generate exemplars from each of four semantic/syntactic categories (animals, tools, common nouns and verbs) and three letters (G, E and T). Data from 13 schizophrenic subjects and 15 sex-, age- and pre-morbid-IQ-matched control subjects revealed that patients' overall performance on both the semantic and letter fluency tasks was impaired. While differential impairment on specific semantic categories was noted between groups, no differential effects relating to task duration or testing session were present. Further, by comparing the number of novel words produced in the three testing sessions, we found the groups to be equivalent, a finding we take to suggest that schizophrenic patients' lexicon is intact. Covarying current IQ eliminated the group difference robustly for letter fluency, while only marginally for semantic fluency. Our data revealed the presence of impairment in semantic and letter fluency tasks in schizophrenic patients consistent with previous reports, and also that patients were differentially impaired on semantic categories.     

Semantic fluency is impaired but phonemic and design fluency are preserved in early-onset schizophrenia

Impairments of verbal fluency are recognised in adult-onset schizophrenia but their presence in early-onset schizophrenia is not well established. This study investigated the extent and character of verbal fluency disturbance in young patients close to illness onset. Thirty-three adolescents with DSM-IV schizophrenia and 33 controls completed phonemic and semantic fluency tests and a free design fluency test. Patients had significantly impaired semantic fluency compared to controls but no impairment on phonemic or design fluency. The difference between patients and controls for semantic fluency remained significant when corrected for age and IQ. These results lend support to the hypothesis that impaired semantic fluency may be an early trait marker of schizophrenia that is potentially related to a failure of lateralisation of language.