Clustering and switching on verbal fluency: the effects of focal frontal- and temporal-lobe lesions

Using what we know: Consequences of intentionally retrieving gist versus item-specific information

The effect of a prior gist-based versus item-specific retrieval orientation on recognition of objects and words was examined. Prior item-specific retrieval increased item-specific recognition of episodically related but not previously tested objects relative to both conceptual- and perceptual-gist retrieval. An item-specific retrieval advantage also was found when the stimuli were words (synonyms) rather than objects but not when participants overtly named objects during gist-based recognition testing, which suggests that they did not always label objects under general gist-retrieval instructions. Unlike verbal overshadowing, labeling objects during recognition attenuated (but did not eliminate) test- and interference-related forgetting. A full understanding of how retrieval affects subsequent memory, even for events or facts that are not themselves retrieved, must take into account the specificity with which that retrieval occurs.

The Semantic Object Retrieval Test (SORT) in Normal Aging and Alzheimer Disease

OBJECTIVE

To characterize performance on a test of semantic object retrieval (Semantic Object Retrieval Test-SORT) in healthy, elderly subjects and patients with Alzheimer disease (AD).

BACKGROUND

Although the initial presentation of patients with AD often reflects impairment in delayed recall for verbally encoded memory, common complaints of patients with early AD are actually related to semantic memory impairment.

DESIGN

Thirty-eight AD patients and 121 healthy aging controls enrolled in an Alzheimer's Disease Center received a battery of standard neuropsychologic tests including the SORT.

RESULTS

Compared with normal controls, AD patients had SORT memory impairments with significantly more false positive memory errors, fewer correctly produced names, and more substitutions in the name production aspect of the test. SORT had robust test-retest reliability in normals.

CONCLUSIONS

The SORT task provides a direct, specific assessment of semantic memory, and has now been administered to 121 healthy, aging controls for normative ranges of performance, and to AD patients. The task detected semantic memory deficits in approximately half of patients with mild-moderate AD, which is comparable to other studies assessing semantic deficits in AD with less specific measures.

Norwegian Norms and Factor-Structure of Phonemic and Semantic Word List Generation

Word list generation (WLG) tasks are used world wide as measures of executive function, although the tests are sensitive also to deficits in other cognitive functions. Norms derived from English-speaking samples are often used in Norway, even though the consequences of language differences are not yet been assessed. The reliability of WLG testing in Norway is increased by the norms presented in the first part of the study. The validity of WLG tests as measures of executive function is addressed in the second part, by performing a factor-analysis of neuropsychological performance in a mixed psychiatric sample. Education contributed most to performance. There were no sex-differences in overall performance. Factor analysis indicated that phonemic WLG is a more specific measure of executive function than semantic WLG. Semantic WLG correlated higher with basal processing speed, thus being more sensitive to aging. In conclusion the clinical neuropsychologist is advised to control for reduction in basal processing speed before interpreting WLG scores as specific deficits in executive function. The Norwegian norms correspond well with most comparable studies in other languages, thus failing to show any language specific effects.

Shared executive dysfunctions in unaffected relatives of patients with autism and obsessive-compulsive disorder

BACKGROUND

Executive dysfunctions have been studied as a potential endophenotype associated with the genetic basis of autism. Given that recent findings from clinical and molecular genetic studies suggest that autism and obsessive-compulsive disorder (OCD) could share a common pattern of heritability, we assessed executive functions as a possible common cognitive endophenotype in unaffected family members of individuals with either autism or OCD.

METHODS

Five tests assessing executive functions (Tower of London, verbal fluency, design fluency, trail making and association fluency) were proposed to 58 unaffected first-degree relatives (parents and siblings) of probands with autism and 64 unaffected first-degree relatives of OCD patients. Results were compared with those of 47 healthy controls matched for age, sex, and level of education.

RESULTS

In the Tower of London test, both groups of unaffected relatives showed significantly lower scores and longer response times compared with controls. No differences were observed between autism and OCD relatives and healthy controls in the four other tasks (verbal fluency, design fluency, trail making test and association fluency).

CONCLUSIONS

Our findings show the existence of executive dysfunction in the unaffected first-degree relatives of probands with OCD, similar to those observed in the relatives of patients with autism. These results support and extend previous cognitive studies on probands indicating executive dysfunctions in autism and OCD. Planning and working memory processes could thus represent a common cognitive endophenotype in autism and OCD that could help in the identification of genes conferring vulnerability to these disorders.

Costs of a predictable switch between simple cognitive tasks following severe closed-head injury

The authors used a predictable, externally cued task-switching paradigm to investigate executive control in a severe closed-head injury (CHI) population. Eighteen individuals with severe CHI and 18 controls switched between classifying whether a digit was odd or even and whether a letter was a consonant or vowel on every 4th trial. The target stimuli appeared in a circle divided into 8 equivalent parts. Presentation of the stimuli rotated clockwise. Participants performed the switching task at both a short (200 ms) and a long (1,000 ms) preparatory interval. Although the participants with CHI exhibited slower response times and greater switch costs, similar to controls, additional preparatory time reduced the switch costs, and the switch costs were limited to the 1st trial in the run. These findings indicate that participants with severe CHI were able to take advantage of time to prepare for the task switch, and the executive control processes involved in the switch costs were completed before the 1st trial of the run ended.

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.

The psychometric equivalence of two alternate forms of the Controlled Oral Word Association Test

The equivalence of forms CFL and PRW of the Controlled Oral Word Association Test (COWAT; Benton, de Hamsher, & Sivan; 1994) was examined in samples of healthy college students. Both novel words and qualitative scores (e.g., clusters, switches) were examined using null hypothesis statistical testing (NHST) and inferential confidence intervals (Tryon, 2001). Study 1 used a within-subjects design (n = 66) to examine form equivalence in persons who completed versions CFL and PRW. No mean differences were found for any index, and only one (mean cluster size) differed when examining the standard deviations across forms. Inferential confidence intervals were constructed and Rg (maximum probable difference) values were small and, when compared to prior research, less than the standard error of measure associated with using a single form. In Study 2, we employed a between-subjects design (n = 208) and found that the use of each version generated comparable normative data and correlations among scores. These studies suggest that versions CFL and PRW are best viewed as alternate (rather than parallel) forms at this time; however, they are likely to produce comparable results for most purposes. We discuss the use of inferential confidence intervals to examine form equivalence and directions for future work.

Executive function and the frontal lobes: a meta-analytic review

Currently, there is debate among scholars regarding how to operationalize and measure executive functions. These functions generally are referred to as "supervisory" cognitive processes because they involve higher level organization and execution of complex thoughts and behavior. Although conceptualizations vary regarding what mental processes actually constitute the "executive function" construct, there has been a historical linkage of these "higher-level" processes with the frontal lobes. In fact, many investigators have used the term "frontal functions" synonymously with "executive functions" despite evidence that contradicts this synonymous usage. The current review provides a critical analysis of lesion and neuroimaging studies using three popular executive function measures (Wisconsin Card Sorting Test, Phonemic Verbal Fluency, and Stroop Color Word Interference Test) in order to examine the validity of the executive function construct in terms of its relation to activation and damage to the frontal lobes. Empirical lesion data are examined via meta-analysis procedures along with formula derivatives. Results reveal mixed evidence that does not support a one-to-one relationship between executive functions and frontal lobe activity. The paper concludes with a discussion of the implications of construing the validity of these neuropsychological tests in anatomical, rather than cognitive and behavioral, terms.

National Institute of Neurological Disorders and Stroke-Canadian Stroke Network vascular cognitive impairment harmonization standards

BACKGROUND AND PURPOSE

One in 3 individuals will experience a stroke, dementia or both. Moreover, twice as many individuals will have cognitive impairment short of dementia as either stroke or dementia. The commonly used stroke scales do not measure cognition, while dementia criteria focus on the late stages of cognitive impairment, and are heavily biased toward the diagnosis of Alzheimer disease. No commonly agreed standards exist for identifying and describing individuals with cognitive impairment, particularly in the early stages, and especially with cognitive impairment related to vascular factors, or vascular cognitive impairment.

METHODS

The National Institute for Neurological Disorders and Stroke (NINDS) and the Canadian Stroke Network (CSN) convened researchers in clinical diagnosis, epidemiology, neuropsychology, brain imaging, neuropathology, experimental models, biomarkers, genetics, and clinical trials to recommend minimum, common, clinical and research standards for the description and study of vascular cognitive impairment.

RESULTS

The results of these discussions are reported herein.

CONCLUSIONS

The development of common standards represents a first step in a process of use, validation and refinement. Using the same standards will help identify individuals in the early stages of cognitive impairment, will make studies comparable, and by integrating knowledge, will accelerate the pace of progress.

Differential verbal fluency deficits in the preclinical stages of Alzheimer's disease and vascular dementia

We examined patterns of early and late word generation in category and letter fluency among persons in the preclinical stages of Alzheimer's disease (AD) and vascular dementia (VaD). The sample consisted of 20 preclinical VaD persons, 66 preclinical AD persons, and 267 control persons, sampled from the community. Persons in the preclinical phase of AD and VaD were similarly impaired in letter fluency, although the preclinical VaD group outperformed their AD counterparts in category fluency. This pattern of results is consistent with the notion that category fluency is relatively more dependent on the medial-temporal lobe, whereas letter fluency relies more on frontal regions. The patterns of fluency impairment in preclinical AD and VaD generalized across early and late word retrieval.

The effects of stereotype threat on cognitive function in ecstasy users

Stereotype threat occurs when individuals, believed to be intellectually inferior, perform badly on cognitive tests they perceive to confirm stereotypes about them. Due to the wide media coverage of studies purporting to show cognitive deficits in ecstasy users it is possible that they experience stereotype threat. This study tested ecstasy and non-ecstasy using polysubstance misusers on a variety of cognitive tests after they had been exposed to stereotype threat. This priming consisted of exposing them to information about the long-term effects of ecstasy which either stated that ecstasy caused memory loss or that it did not. Ecstasy users that had been primed that ecstasy did not cause cognitive deficits performed better than the other three groups on the delayed portion of the prose recall task from the Rivermead Behavioural Memory Test battery. There were no other statistically significant differences between any of the groups on any of the other cognitive tests used. This suggests that stereotype threat exists in ecstasy users and may be influencing their performance in experiments designed to identify cognitive deficits. In order to prevent this occurring in future studies, experimenters must be careful how they conduct their experiments and discuss their results with the media.

Sex differences in clustering and switching in verbal fluency tasks

Sex differences in executive speech tasks, favoring women, have been noted in behavioral studies and functional imaging studies. In the present study, the clustering and switching components of semantic and phonemic verbal fluency tests were examined in 40 healthy men and 40 healthy women. Possible sex differences in the influence of cognitive factors such as speed of information processing, word knowledge, and/or verbal long-term memory on these verbal fluency factors were also assessed. The results showed that women switched more often between categories in the phonemic fluency test, whereas men showed a trend toward a larger cluster size leading to a smaller total number of words generated. Additionally, higher performance on the Digit Symbol test was associated with better performance on the semantic and phonemic verbal fluency test in men, whereas in women, better memory performance was associated with better performance on these verbal fluency tests. Our data indicate that men and women are using different processing strategies for phonemic verbal fluency tests to optimize verbal fluency task performance. In the current study, women adopted a more successful strategy of balancing clustering and switching in the phonemic fluency task.

The Development of Naming and Word Fluency: Evidence From Hebrew-Speaking Children Between Ages 8 and 17

Naming and word fluency tests are commonly used in neuropsychological evaluations of both children and adults. The current work examines at which age performance on these tests reaches adult level. One hundred fifty children, 30 in each of 5 age groups (8-9, 10-11, 12-13, 14-15, 16-17), and 30 adults ages 18 to 29, participated in the study. Participants completed a Hebrew naming test, a three-letter phonemic fluency task, and a three-category semantic fluency task (animals, fruits and vegetables, and vehicles). Results show that all measures increase steadily from age 8 to age 17. No difference between the 16- to 17-year-old adolescents and the adults was found on the naming test and on the phonemic fluency task, but such a difference was documented for semantic fluency. The relative contribution of the maturation of vocabulary and the development of efficient retrieval processes to performance on naming and fluency tasks is discussed.

Treating anomia in semantic dementia: Improvement, maintenance, or both?

A treatment programme for AK, an anomic patient with semantic dementia is described. The programme was based on home practice and resulted in re-learning the names of some objects AK could not name and/or comprehend prior to the treatment. The effects of treatment were still present one month post-treatment for items that AK could not name but could comprehend prior to treatment. In addition to items that AK could not name, items that she could both understand and name were also included in the programme. This allowed us to evaluate the influence of practice on the retention of words that appeared to be intact at the outset of the investigation. Results indicated that practice delayed the progression of loss. In addition, the programme was designed jointly with AK who made many important decisions related to treatment.

Role of the left inferior frontal gyrus in covert word retrieval: neural correlates of switching during verbal fluency

Word retrieval ability is commonly assessed with a semantic verbal fluency task, in which subjects must produce a list of exemplars of a category (e.g., animals). The order in which exemplars are produced is not random; rather, subjects tend to produce "clusters" of semantically related items (e.g., cow, pig, sheep) and occasionally "switch" to other clusters (e.g., lion, tiger, bear). Patients with frontal lobe pathology (associated with focal lesions or Parkinson's disease) exhibit reduced output on semantic fluency tasks that has been characterized as a reduction in switching, in contrast to other impaired patient groups who produce normal switches but smaller clusters (e.g., [Troyer, A. K., Moscovitch, M., Winocur, G., Leach, L., & Freedman, M. (1998). Clustering and switching on verbal fluency tests in Alzheimer's and Parkinson's disease. Journal of the International Neuropsychological Society, 4(2), 137-143]). The ability to initiate a switch between two semantic categories may require the selection of weakly activated representations over active (but already reported) representations. Previous studies have shown that increased demands on selection among competing representations are associated with activity in the left inferior frontal gyrus (LIFG) and with deficits in patients with lesions including LIFG [Thompson-Schill, S. L., Jonides, J., Marshuetz, C., Smith, E. E., D'Esposito, M., Kan, I. P., et al. (2002). Effects of frontal lobe damage on interference effects in working memory. Cognitive Affective & Behavioral Neuroscience, 2(2), 109-120; Thompson-Schill, S. L., Swick, D., Farah, M. J., D'Esposito, M., Kan, I. P., & Knight, R. T. (1998). Verb generation in patients with focal frontal lesions: A neuropsychological test of neuroimaging findings. Proceedings of the National Academy of Sciences of the United States of America, 26, 14792-14797]. In the present study, we investigated the neural correlates of switching in the verbal fluency task, and in particular, the role of the LIFG in switching between semantic sub-categories. We observed greater activation in the LIFG during switching compared to free generation (Experiment 1) and self-reported clustering (Experiment 2), which is consistent with the hypothesis that the switching mechanism is subserved by the LIFG due to high semantic selection demands.

Discriminating patients with frontal-lobe epilepsy and temporal-lobe epilepsy: utility of a multilevel design fluency test

Patients with frontal-lobe epilepsy (FLE) or temporal-lobe epilepsy (TLE) and matched control participants were given a design fluency test that assessed nonverbal fluency and switching ability. Patients with FLE generated fewer designs in the switching condition relative to the TLE patients and controls, whereas group differences did not emerge in the basic fluency conditions. When the side of the seizure focus and the presence or absence of a structural lesion were considered in patients with FLE, only those with left-lesional FLE generated fewer designs than controls did in the switching condition. Furthermore, patients with left-lesional and nonlesional FLE produced a greater proportion of set-loss errors than did controls. These results indicate that patients with FLE are impaired when they must simultaneously generate new designs and engage in cognitive switching; however, the pattern of impairment may depend on the side of the seizure focus and the presence of a structural lesion.

Effects of age and hypertension status on cognition: the Veterans Affairs Normative Aging Study

The authors examined the influence of age and hypertensive status (normotensive, controlled, untreated, or uncontrolled) on several cognitive tests via multiple regression in 357 nondemented, community-dwelling older men (mean age=67 years) whose hypertensive status was stable over 3 years and who had no medical comorbidities. Age was negatively associated with performance on all but 1 test. Age interacted with hypertensive status on verbal fluency and word list immediate recall; older uncontrolled hypertensives exhibited significantly larger age decrements on these tests compared with normotensives. These findings suggest that uncontrolled hypertension produces specific cognitive deficits beyond those attributable to age alone. These and previous findings illustrate that health conditions such as hypertension should be regularly considered in studies of "normal" cognitive aging.

[Is age at onset associated with executive dysfunction in obsessive-compulsive disorder?]

In obsessive-compulsive disorder (OCD), clinical, neurobiological and genetic differences have been reported according to age at onset (AAO). Given the importance of identifying homogeneous subtypes in complex hete-rogeneous disorders such as OCD, it would be particularly useful to identify a specific cognitive profile associated with early-onset OCD. Although impaired cognition has repea-tedly been demonstrated in OCD patients, discrepancies between studies have hampered the identification of a precise cognitive dysfunction. Executive dysfunction has often been reported, but findings have not always been replicated. The aim of this study was to assess executive functions in 30 patients according to their AAO. The sample consisted of 15 early-onset and 15 late-onset OCD patients and 22 normal controls, matched for age, sex and socio-economic status. Various aspects of executive function were assessed with five neuropsychological tests: Tower of London, Trail Making Test, Verbal Fluency, Design Fluency and Association Fluen-cy. The 30 OCD patients obtained lower total scores than the controls in the Tower of London test and association fluen-cy task (p<0.05 and p<0.001, respectively). Impairments were more marked for the early-onset group, with no effect of gender or age at interview. Deficits in specific aspects of frontal lobe function were found in the OCD group and were particularly pronounced within the early-onset group. These findings confirm clinical data suggesting that OCD patients can be subtyped according to age at onset and that OCD patients present unusual cognitive characteristics. They also support the hypothesis that early-onset OCD might be a rele-vant subgroup characterised both by a particular clinical profile and by specific cognitive characteristics.

Flexible remembering

Although highly specific memory is critical in many contexts, the ability to recall knowledge in a more abstract or "gist-based" manner is crucial in allowing transfer of learning to new situations and to complex forms of thought such as using analogies and drawing inferences based on the classification of events and objects. Yet it is unknown whether we can flexibly and intentionally alternate on demand between recollection of gist and recollection of detail, particularly for events from a single context. In a randomly cued test of item-specific versus category-based recognition, younger--and to a lesser extent, older--adults demonstrated such flexible remembering. Gist control was higher in younger than in older adults, and in older adults it correlated with measures of frontal function.

Neuropsychological assessment of executive functions in women: effects of age and education

The cognitive processes underlying age-related alterations in tests assumed to reflect frontal lobe functions were investigated with a card sorting test and an alternate semantic fluency task. The tests were administered to 133 healthy women belonging to 3 age groups (range=50-92 years) classed according to 2 education levels. The results revealed a negative association between total word fluency and perseveration in the sorting test. Aging similarly affected performance in both education groups in some components of the tasks (atypical word fluency and sensitivity to distraction). However, aging did not affect performance to the same extent in each education group in other components (particularly those reflecting switching abilities and strategies). This quasi-experimental approach provides useful tools to identify specific processing mechanisms underlying executive functions in normal aging.

The functional neuroanatomy of working memory: contributions of human brain lesion studies

Studies of patients with focal brain lesions remain critical components of research programs attempting to understand human brain function. Whereas functional imaging typically reveals activity in distributed brain regions that are involved in a task, lesion studies can define which of these brain regions are necessary for a cognitive process. Further, lesion studies are less critical regarding the selection of baseline conditions needed in functional brain imaging research. Lesion studies suggest a functional subdivision of the visuospatial sketchpad of working memory with a ventral stream reaching from occipital to temporal cortex supporting object recognition and a dorsal stream connecting the occipital with parietal cortex enabling spatial operations. The phonological loop can be divided into a phonological short-term store in inferior parietal cortex and an articulatory subvocal rehearsal process relying on brain areas necessary for speech production, i.e. Broca's area, the supplementary motor association area and possibly the cerebellum. More uncertainty exists regarding the role of the prefrontal cortex in working memory. Whereas single cell studies in non-human primates and functional imaging studies in humans have suggested an extension of the ventral and dorsal path into different subregions of the prefrontal cortex, lesion studies together with recent single-cell and imaging studies point to a non-mnemonic role of the prefrontal cortex, including attentional control of sensory processing, integration of information from different domains, stimulus selection and monitoring of information held in memory. Our own data argue against a modulatory view of the prefrontal cortex and suggest that processes supporting working memory are distributed along ventral and dorsal lateral prefrontal cortex.

Qualitative features of semantic fluency performance in mesial and lateral frontal patients

Semantic verbal fluency is widely used in clinical and experimental studies. This task is highly sensitive to the presence of brain pathology and is frequently impaired after frontal lesions. Besides the total number of words generated, a qualitative analysis of their sequence can add valuable information about the impaired cognitive components. Thirty-four frontal patients and a group of matched controls were examined. Besides the number of words and subcategories retrieved by each group, we analysed two distinct aspects of the word sequence: the search strategy through a semantically organised store and the ability to switch from one subcategory to another. We checked whether the pattern of impairment changed according to the lesion site within the frontal lobe. Overall, patients produced fewer words than controls. However, only lateral frontal patients presented a reduced semantic relatedness between contiguously produced words and a specifically increased proportion of switches to different subcategories. The performance of lateral frontal patients was in line with the hypothesis of a search strategy impairment and cannot be attributed to a switching deficit. The performance of mesial frontal patients could be ascribed to a general deficit of activation.

Verbal fluency in institutionalized patients with schizophrenia: age-related performance decline

Several studies have reported a relatively stable level of cognitive deficits among patients with schizophrenia regardless of age, while others have suggested continued deterioration with age. We compared the performance of 42 institutionalized patients with schizophrenia and 42 age- and education-matched healthy controls on a semantic and phonemic verbal fluency test. Each group was divided into young participants (<65 years old) and elderly participants (> or =65 years old). We found a fluency condition x diagnostic group x age group interaction on total words produced, a fluency condition x diagnostic group interaction on the number of cluster-related words, and a fluency condition x age group interaction on the number of switches. Patients with schizophrenia generally used similar strategies (i.e., semantic or phonemic cluster-related words and switches) as healthy individuals when generating words, but to a lesser degree. We found a disproportionate decline in the elderly schizophrenic patients relative to that of healthy controls only on the phonemic, relative to the semantic test. This decline in performance appears related to the effects of aging rather than severity or chronicity of illness, duration of institutionalization, or a progressive degenerative process associated with the disorder.

Age-related impairment in executive functioning: updating, inhibition, shifting, and access

Miyake, Friedman, Emerson, Witzki, Howerter and Wager (2000) have argued that the central executive is fractionated consisting of at least three separable component processes: updating, shifting, and inhibition. The Wisconsin Card Sort Test, random letter generation, Brooks spatial sequences, reading and computation span, word fluency, and a measure of dual task performance were administered to 95 individuals aged between 20 and 81, average age 41.89. The executive measures were factor analyzed, using the oblique rotation method, yielding four factors. The factor structure obtained was broadly consistent with Miyake et al's. However, an additional factor, the only one not to show a significant performance decline with age, was also obtained and was believed to reflect the efficiency of access to long-term memory.

Apolipoprotein E and category fluency: evidence for reduced semantic access in healthy normal controls at risk for developing Alzheimer's disease

Two groups of non-demented individuals, who differed on genetic risk for Alzheimer's disease (AD) based on their apolipoprotein E (APOE) genotype, were tested on a category fluency task. Twenty varepsilon4 carriers and twenty varepsilon4 non-carriers were tape recorded while saying animal names for ten minutes. Five measures were examined: total names generated; total clusters; mean cluster size; mean within-cluster retrieval time; and mean between-cluster retrieval time. Groups were matched on age and education and scored as normal on a battery of psychometric tests. The varepsilon4 carriers generated significantly fewer names and clusters, and took significantly longer to access clusters, when compared to the varepsilon4 non-carriers. No group differences were found for cluster size or within-cluster retrieval times. We previously reported [Rosen, V. M., Bergeson, J. L., Putnam, K., Harwell, A., Sunderland, T. (2002). Working memory and apolipoprotein E: What's the connection? Neuropsychologia 40, 2226-2233] that the varepsilon4 carriers in the present study scored significantly lower than the varepsilon4 non-carriers on a measure of working memory/attentional capacity [Operation Span Task, see Turner, M. L., Engle, R. W. (1989). Is working memory capacity task dependent? Journal of Memory and Language 28, 127-154]. In the present study, a significant negative relationship found between span performance and between-cluster retrieval times suggested that reduced attentional capacity may have negatively impacted semantic access for the varepsilon4 carriers. Finally, we found significant relationships between a Trail Making Test [Reitan, R. M. (1992). Trail Making Test, manual for administration and scoring. Tucson, AZ: Reitan Neuropsychology Laboratory] "switch" measure (Form B-Form A) and three of the five fluency measures. The findings suggested that the varepsilon4 carrier's reduced attentional capacity may have interfered with their covertly shifting attention among subcategories in the fluency task, resulting in fewer names and clusters generated and longer times to access clusters.

Category fluency test: effects of age, gender and education on total scores, clustering and switching in Brazilian Portuguese-speaking subjects

Verbal fluency tests are used as a measure of executive functions and language, and can also be used to evaluate semantic memory. We analyzed the influence of education, gender and age on scores in a verbal fluency test using the animal category, and on number of categories, clustering and switching. We examined 257 healthy participants (152 females and 105 males) with a mean age of 49.42 years (SD = 15.75) and having a mean educational level of 5.58 (SD = 4.25) years. We asked them to name as many animals as they could. Analysis of variance was performed to determine the effect of demographic variables. No significant effect of gender was observed for any of the measures. However, age seemed to influence the number of category changes, as expected for a sensitive frontal measure, after being controlled for the effect of education. Educational level had a statistically significant effect on all measures, except for clustering. Subject performance (mean number of animals named) according to schooling was: illiterates, 12.1; 1 to 4 years, 12.3; 5 to 8 years, 14.0; 9 to 11 years, 16.7, and more than 11 years, 17.8. We observed a decrease in performance in these five educational groups over time (more items recalled during the first 15 s, followed by a progressive reduction until the fourth interval). We conclude that education had the greatest effect on the category fluency test in this Brazilian sample. Therefore, we must take care in evaluating performance in lower educational subjects.

The dynamic time course of memory recovery in transient global amnesia

AIMS

To investigate the dynamic time course of transient global amnesia (TGA)--that is, the process of recovery and the interindividual variability--by testing four patients during the day of TGA itself (on three occasions) and at follow up (on two occasions).

METHODS

A specially designed protocol focusing on semantic (both conceptual and autobiographical knowledge) and episodic (both anterograde and retrograde components) memory.

RESULTS

Every patient showed marked impairment of both anterograde and retrograde episodic memory during the acute phase, with a relative preservation of personal and conceptual semantic knowledge. During the following phase, the authors observed similarities and differences among the patients' patterns of recovery. In general, retrograde amnesia recovered before the anterograde amnesia and anterograde episodic memory was recovered gradually in every case. In contrast, shrinkage of retrograde amnesia was more heterogeneous. In two of the patients, this shrinkage followed a chronological gradient and the most remote events were recovered first. In the two other patients, it depended more on the strength of the trace, and there was no temporal gradient. For the latter, an executive deficit could account for difficulties in accessing both conceptual knowledge and autobiographical memories.

CONCLUSIONS

This profile of recovery suggests a "neocortical to medial temporal" process in every case, and the possibility of an additional frontal dysfunction in some cases. Hence, the acute phase seems to be characterised by a common episodic impairment. This variability between subjects appears in the recovery phase with two different patterns of impairment.

A meta-analytic review of verbal fluency performance following focal cortical lesions

A meta-analysis of 31 studies with 1,791 participants was conducted to investigate the sensitivity of tests of verbal fluency to the presence of focal cortical lesions. Relative to healthy controls, participants with focal frontal injuries had large and comparable deficits on phonemic (r = .52) and semantic (r = .54) fluency. For frontal but not nonfrontal patients, phonemic fluency deficits qualified as differential deficits when compared with IQ and psychomotor speed; phonemic fluency was also more strongly and more specifically related to the presence of frontal lesions than the Wisconsin Card Sorting Test scores. In contrast, temporal damage was associated with a lesser deficit on phonemic fluency (r = .44) but a larger deficit on semantic fluency (r = .61).

What is measured by verbal fluency tests in schizophrenia?

INTRODUCTION

Schizophrenia patients perform below the norm on verbal fluency tests. The causes for this are unknown, but defective memory, executive functioning and psychomotor speed may play a role.

METHOD

We examined 50 patients with schizophrenia and related disorders, and 25 healthy controls with a cognitive test battery containing tests for verbal memory, executive functioning and psychomotor speed, and a categorical fluency test.

RESULTS

Patients obtained significantly lower test results than the controls on most cognitive measures including the verbal fluency test. During the fluency test, they formed as many clusters, and switched as often between clusters as the controls did, but they generated fewer words per cluster. Interestingly, in the control group, fluency performance was predicted by memory and executive functioning, but not by psychomotor speed. In patients, verbal fluency was predicted by psychomotor speed, but not by memory or executive functioning.

DISCUSSION

We conclude that psychomotor speed could be a crucial factor in cognition, and its influence on cognitive test performance should be considered in schizophrenia research. Furthermore, these data illustrate the importance of qualitative analysis of cognitive impairments in schizophrenia patients, as traditional cognitive tests often only provide quantitative information.

Verbal fluency output in children aged 7-16 as a function of the production criterion: qualitative analysis of clustering, switching processes, and semantic network exploitation

Developmental changes in children's verbal fluency were explored in this study. One hundred and forty children aged from 7 to 16 completed four verbal fluency tasks, each with a different the production criterion (letter, sound, semantic, and free). The age differences were analyzed both in terms of number of words produced, and clustering, switching, and semantic network exploration. Analysis of the number of words produced showed a larger difference between the 7-8- and the 9-10-year-olds in semantic than in letter fluency, but this difference gradually disappeared with increasing age for semantic fluency while remaining constant for letter fluency. In letter fluency production, age modified both the number of switches and clusters formed whereas in semantic fluency tasks, only cluster size changed with age. Concerning the semantic network exploration indicators derived from the supermarket fluency task, the number of categories sampled increased from 11 to 12 years, but efficient semantic exploitation occurred only after the age of 13-14 years. These results are discussed in terms of the development of strategic retrieval components and categorical knowledge.

Manipulation of frontal brain asymmetry by cognitive tasks

The purpose of the present study was to evaluate whether verbal fluency tasks may specifically induce relatively greater left than right hemispheric activation in the dorsolateral prefrontal cortex. The effectiveness of the manipulation was evaluated by EEG, which was recorded during performance of the verbal fluency task and during two control conditions, i.e., a baseline condition without cognitive demands, and a mental arithmetic task, respectively. The results demonstrate that the desired effect can only be achieved in individuals with good performance on the verbal fluency task. Good and poor performers do not only differ in lateral asymmetry, but also in the most affected region within the prefrontal cortex. Whereas good performers show relatively increased activation in the cortical region and hemisphere putatively most specialized for this kind of task (i.e., the left dorsolateral frontal cortex), poor performers show a marked shift of frontopolar asymmetry to the right.

The verbal fluency task in the Greek population: normative data, and clustering and switching strategies

We assessed 300 healthy adults in Greece on measures of semantic and phonemic verbal fluency in order to develop norms for the Greek population. We also evaluated the strategies that the participants used spontaneously in order to maximize word production, namely clustering and switching techniques. Our tasks comprised three semantic and three phonemic categories. Consistent with previous investigations of English-speaking samples, we found a contribution of demographic variables to word fluency. Specifically, level of education contributed to total word production, number of switches, and number of repetitive responses on both semantic and phonemic tasks, and the average cluster size only on the phonemic task. Age contributed to total word production and cluster size on the semantic task, and to number of switches on both semantic and phonemic tasks. Sex contributed only to total word production on the semantic task. In our sample, clustering and switching strategies were related to total word production on both tasks, suggesting that these strategies were used effectively. We present tables of normative data stratified by age and level of education. We have also included detailed guidelines for scoring clusters relevant to the Greek population.

The Effects of Alzheimer's Disease on Item Output in Verbal Fluency Tasks

We collected category fluency data from several moderate-to-large samples of participants at three different sites: the New York University Aging and Dementia Center, the Oregon Health Services Aging and Dementia Research Center, and the Einstein Aging Study at the Albert Einstein College of Medicine. These data were analyzed by calculating the average relative frequency (e.g., typicality) of the category members generated by each participant. Alzheimer's disease (AD) patients recalled fewer atypical members of common taxonomic categories than did the elderly control group. In addition, the probability of producing an item declined at a greater rate for AD patients than for the elderly control group over the duration of the task. According to sequential sampling models, this latter result implies that the rate at which AD patients search memory must be slower than the search rate of the elderly controls.

Cognitive and motor functioning in a patient with selective infarction of the left basal ganglia: evidence for decreased non-routine response selection and performance

Focal damage to the basal ganglia is relatively rare, and little is known about the cognitive effects of damage to specific basal ganglia structures. A 28-year-old, highly educated male (patient RI) sustained a unilateral left ischemic infarction involving primarily the putamen and secondarily the head of the caudate and the anterior internal capsule. Two detailed neuropsychological assessments, at 3 and 16 months post-infarction, revealed that a majority of cognitive abilities were spared. RI's general intelligence, simple attention, concept formation, cognitive flexibility, and explicit memory were unaffected. Select cognitive abilities were affected, and these appeared to be related to direct involvement of the putamen and/or to indirect disruption of circuits between the basal ganglia and frontal lobes. Consistent with involvement of the left putamen, RI showed micrographia with his right hand. Interestingly, his micrographia was context-dependent, appearing only when verbal expression was involved (e.g., present when writing spontaneously, but not when copying sentences or when drawing). Evidence of disruption to frontal systems included variably decreased sustained attention, mildly decreased ability to generate words and to generate ideas, and significantly impaired abstraction ability in both verbal and visual modalities. Although there are several possible interpretations for these findings, this pattern of cognitive and motor functioning is consistent with neuroimaging research suggesting that the frontal/subcortical circuit between the putamen and frontal motor areas plays a role in non-routine response selection and performance.

Executive skills in Klinefelter's syndrome

Executive skills are those involved in concept formation, problem solving, switching tasks, inhibiting inappropriate responses, initiating rapid and fluent responses, planning and sustained attention. Different patterns of disorder amongst these skills have been found in several developmental abnormalities including autism, attention deficit hyperactivity disorder (ADHD) and Turner's syndrome (TS). This study explored, for the first time, executive skills in children with Klinefelter's syndrome (KS), a sex chromosome abnormality in which there is one or more additional X-chromosomes. Intelligence in KS is normal but there is academic underachievement. A battery of executive tasks was administered, in a series of case studies, to three 10-year-old boys with KS and to controls matched for age, sex and intelligence. The results demonstrate that children with KS have impairments in executive skills. However, the pattern of impairment is task-specific. There is evidence from multiple tasks of impairment in inhibitory skills, for each case of KS. In contrast, concept formation, problem solving, task switching and speeded responding are normal. These results support theories that argue for distinct sub-components of executive skills within development that may develop relatively independently. The results have relevance for modelling both child and adult executive systems. They also confirm that an additional X-chromosome has highly selective effects upon the consequent cognitive phenotype seen in development.

Relation of “Sense Of Self” to Executive Function Performance in Parkinson's Disease

BACKGROUND

Recent reports have linked impairment of various aspects of the sense of self to frontal brain dysfunction. Independent evidence suggests that patients with Parkinson's disease exhibit impairment on cognitive tasks that depend on the frontal lobes.

OBJECTIVE

To test the hypothesis (1) that the sense of self would be impaired in some persons with Parkinson's disease and (2) that this impairment would be linked to frontal dysfunction.

METHODS

Sentence completion tests of identity development ("self-test") and measures of frontal and temporal lobe functioning were administered to 20 people with Parkinson's disease and to 10 age-matched healthy controls.

RESULTS

While self-test responses significantly correlated with performance scores on tests of executive function (for Parkinson's disease patients only) but not temporal lobe function (as measured by "clustering" rates on a fluency task), we found no significant differences in mean self-test scores between persons with Parkinson's disease and age-matched controls. Analysis of the 160 self-test responses revealed a shift toward conformist responses in Hoehn-Yahr stage III as compared with stage II Parkinson's disease patients.

CONCLUSIONS

While the sense of self changes as a function of disease stage, the core experience of self in Parkinson's disease is intact but may depend, in part, on frontal lobe function.

Frontal lobe dysfunctions in Korsakoff's syndrome and chronic alcoholism: continuity or discontinuity?

The effect of long-term heavy alcohol consumption on brain functions is still under debate. The authors investigated a sample of 17 Korsakoff amnesics, 23 alcoholics without Korsakoff's syndrome, and 21 controls with peripheral nerve diseases, matched for intelligence and education. Executive functions were examined for word fluency, the modified Wisconsin Card Sorting Test, an alternate response task, and an "n-back" working memory task. Korsakoff amnesics, but not alcoholics, showed a marked memory impairment. They also scored lower in each of the executive tasks-the alcoholics only in the alternate response task. This task also correlated with the years of the alcohol dependency. First, the authors conclude that Korsakoff's syndrome is associated not only with a memory impairment but also with a global executive deficit. Second, the decline in the ability to alternate between different responses argues for a restricted neurotoxic effect of alcohol on some frontal lobe areas.

Deficit of verb generation in nondemented patients with Parkinson's disease

Clinical and neuroimaging studies have shown that verb processing suggests a preferential participation of a prefrontal network, which is dysfunctional in Parkinson's disease (PD). To assess a verb processing deficit in PD, we compared noun- and verb-generation tasks for 34 nondemented PD patients (according to the Dementia Rating Scale) with 34 matched normal subjects, using two intracategory tasks (noun/noun and verb/verb generation) and two intercategory tasks (noun/verb and verb/noun generation). PD patients were significantly impaired in the two tasks involving verb production, i.e., verb/verb and noun/verb generation, whereas their performance was similar to those of controls in the two tasks requiring noun production. For the two impaired tasks, we assessed 1) the influence of lexical competition that corresponds to the presence of several candidate words for a given stimulus; 2) the influence of slight cognitive dysfunction; and 3) the influence of motor deficit. Significant correlations were found between DRS scores and performance on the noun/verb task, and no significant correlations were found between lexical competition or motor deficit and performance. The specific deficit for verb production in PD patients is discussed in relation to deficits affecting either action or grammatical representations.

Qualitative analysis of verbal fluency in depression

The aim of this study was to analyze qualitative aspects of verbal fluency in depression. Phonemic and semantic output was scored for word clustering and switching between clusters in depressed patients and normal control subjects. Depressed patients (n=25) and normal control subjects (n=19) were administered both phonemic and semantic fluency tasks. All patients were also evaluated with executive card sorting tests. Patients with depression produced fewer words on the semantic fluency task than controls and showed normal performance on the phonemic fluency tasks. The deficit on semantic fluency of depressed patients was related to a reduced number of switches with normal cluster sizes. The number of switches in depression was associated with a reduced ability to shift mental set on card sorting tests, suggesting that verbal fluency impairment reflects general executive problems in depression.

The role of prefrontal cortex in working-memory capacity, executive attention, and general fluid intelligence: an individual-differences perspective

We provide an "executive-attention" framework for organizing the cognitive neuroscience research on the constructs of working-memory capacity (WMC), general fluid intelligence, and prefrontal cortex (PFC) function. Rather than provide a novel theory of PFC function, we synthesize a wealth of single-cell, brain-imaging, and neuropsychological research through the lens of our theory of normal individual differences in WMC and attention control (Engle, Kane, & Tuholski, 1999; Engle, Tuholski, Laughlin, & Conway, 1999). Our critical review confirms the prevalent view that dorsolateral PFC circuitry is critical to executive-attention functions. Moreover, although the dorsolateral PFC is but one critical structure in a network of anterior and posterior "attention control" areas, it does have a unique executive-attention role in actively maintaining access to stimulus representations and goals in interference-rich contexts. Our review suggests the utility of an executive-attention framework for guiding future research on both PFC function and cognitive control.

Declines in switching underlie verbal fluency changes after unilateral pallidal surgery in Parkinson's disease

Declines in verbal fluency are consistently reported in patients with Parkinson's disease (PD) after pallidal surgery. In the present study, the clustering and switching components of semantic or category fluency (oral naming of items obtainable in supermarkets) were examined at baseline and four months after unilateral deep brain stimulation or pallidotomy in 45 patients with PD (30 left, 15 right pallidal surgery). Post-operative declines were observed for supermarket fluency total score and switching, but not for average cluster size. These findings support the proposal that semantic fluency decrements after pallidal surgery reflect a disruption of frontal-basal ganglia circuits mediating efficient shifting between semantic categories, or perhaps efficient access to categories, rather than a degradation of semantic stores.

Syllogistic reasoning and cognitive ageing

Gilinsky and Judd (1994) demonstrated that age-related impairment in syllogistic reasoning was in part due to reduced working-memory capacity. A total of 30 older (average age 66 years) and 34 younger persons (average age 24 years) were tested on syllogisms of various types as well as on other measures. Syllogistic reasoning was significantly correlated with education, processing speed, word span, and word fluency. Correlations with visuo-spatial processing and random letter generation were just short of significance. Syllogistic reasoning performance declined with age, although the deficit was no longer statistically significant following control for age-related differences in information-processing speed. On the other hand the inclusion of word fluency as an additional covariate boosted the apparent age effect, returning it to statistical significance. Thus it is possible that cognitive processes outside of working memory might underpin at least part of the apparent age deficit. This possibility is evaluated in the light of neuropsychological evidence implicating the prefrontal cortex in both the processing of syllogisms and more generally in cognitive ageing.

Verbal fluency in Huntington's disease: a longitudinal analysis of phonemic and semantic clustering and switching

Two underlying components of verbal fluency tasks have been identified as clustering (the ability to generate successive words within a sub-category) and switching (the ability to shift from one sub-category to another). Selective impairment of switching ability occurs in patients with frontostriatal pathology, whilst clustering ability is compromised with temporal lobe dysfunction. Letter fluency tasks have been shown to be especially sensitive to frontostriatal deficits, whereas, category fluency tasks tend to be compromised by temporal lobe pathology. This study examined two types of verbal fluency task (letter fluency and category fluency) using two levels of analysis (phonemic and semantic) for clustering and switching measures. The performance of 21 frontostriatally compromised Huntington's disease (HD) patients was followed over an average of 3.5 annual follow-up visits. HD patients showed a significant reduction of correctly generated words over time, together with a significant increase in word repetitions. Phonemic switching decreased significantly over time for both letter and category fluency. Semantic switching, however, remained stable over time for both verbal fluency tasks. Clustering (both semantic and phonemic) likewise remained stable and did not vary longitudinally for either letter or category fluency. Hence, phonemic switching alone drove verbal fluency performance and this selective impairment can be explained by the progressive involvement of frontostriatal circuitry in the natural progression of HD.

Oral fluency and narrative production in children with Turner's syndrome

Despite good verbal skills, children with Turner's syndrome (TS) have been found to perform poorly on oral fluency tasks. Explanations for this impairment were explored in a study of 9-12-year-old children with TS. The children with TS were found, as expected, to have impaired levels of retrieval on initial letter fluency tasks, in comparison to their peers. Children with TS were also found to have receptive vocabularies which were significantly better than controls, indicating that the weak performance on oral fluency cannot be attributed to lower vocabulary levels. Naming skills were normal for children with TS, indicating that oral fluency scores cannot be attributed to generalised problems with lexical access. Analysis of the content of fluency performance indicated clusters of words within sub-categories which were of normal size but there were fewer switches between clusters than for controls and fewer returns to previously successful clusters. Additionally, a significantly larger proportion of the words generated were of low frequency (e.g. Assyrian, antediluvian) and the children with TS did not thereby show a normal frequency effect in word retrieval. One explanation is that these reflect abnormal action of executive language retrieval processes. Within narrative production, picture description was normal. However, in relation to narrative tasks, hypothesised to place greater executive demands, there was impairment which was significantly greater for narratives of yesterday than narratives of organising a party. This impairment within the narrative generation tasks could be attributable to a selective impairment within executive retrieval skills, or could represent an impairment in episodic memory or the executive processes involved in its retrieval.

Adult clinical neuropsychology: lessons from studies of the frontal lobes

Clinical neuropsychologists have adopted numerous (and sometimes conflicting) approaches to the assessment of brain-behavior relationships. We review the historical development of these approaches and we advocate an approach to clinical neuropsychology that is informed by recent findings from cognitive neuroscience. Clinical assessment of executive and emotional processes associated with the frontal lobes of the human brain has yet to incorporate the numerous experimental neuroscience findings on this topic. We review both standard and newer techniques for assessment of frontal lobe functions, including control operations involved in language, memory, attention, emotions, self-regulation, and social functioning. Clinical and experimental research has converged to indicate the fractionation of frontal subprocesses and the initial mapping of these subprocesses to discrete frontal regions. One anatomical distinction consistent in the literature is that between dorsal and ventral functions, which can be considered cognitive and affective, respectively. The frontal lobes, in particular the frontal poles, are involved in uniquely human capacities, including self-awareness and mental time travel.

On the dissociation between clustering and switching in verbal fluency: comment on Troyer, Moscovitch, Winocur, Alexander and Stuss

Troyer, Moscovitch, Winocur, Alexander and Stuss (Neuropsychologia 36 (1998) 499) used a procedure originally introduced by Troyer, Moscovitch and Winocur (Neuropsychology 11 (1997) 138) for distinguishing two different components of verbal fluency-clustering and switching-in frontal and temporal-lobe patients. Application of this procedure yielded results that suggested a frontal-lobe switching deficit, but intact 'clustering'. I demonstrate here that the proposed procedure may lead to incorrect conclusions because it does not allow an unambiguous dissociation between a general reduction in processing speed and a selective switching deficit. Some implications of this critique for inferences about the neurocognitive components involved in verbal fluency tasks are discussed.