Contribution of specific cognitive processes to executive functioning in an aging population

Validity of the NIH toolbox cognitive battery in a healthy oldest-old 85+ sample

OBJECTIVE

To evaluate the construct validity of the NIH Toolbox Cognitive Battery (NIH TB-CB) in the healthy oldest-old (85+ years old).

METHOD

Our sample from the McKnight Brain Aging Registry consists of 179 individuals, 85 to 99 years of age, screened for memory, neurological, and psychiatric disorders. Using previous research methods on a sample of 85 + y/o adults, we conducted confirmatory factor analyses on models of NIH TB-CB and same domain standard neuropsychological measures. We hypothesized the five-factor model (Reading, Vocabulary, Memory, Working Memory, and Executive/Speed) would have the best fit, consistent with younger populations. We assessed confirmatory and discriminant validity. We also evaluated demographic and computer use predictors of NIH TB-CB composite scores.

RESULTS

Findings suggest the six-factor model (Vocabulary, Reading, Memory, Working Memory, Executive, and Speed) had a better fit than alternative models. NIH TB-CB tests had good convergent and discriminant validity, though tests in the executive functioning domain had high inter-correlations with other cognitive domains. Computer use was strongly associated with higher NIH TB-CB overall and fluid cognition composite scores.

CONCLUSION

The NIH TB-CB is a valid assessment for the oldest-old samples, with relatively weak validity in the domain of executive functioning. Computer use's impact on composite scores could be due to the executive demands of learning to use a tablet. Strong relationships of executive function with other cognitive domains could be due to cognitive dedifferentiation. Overall, the NIH TB-CB could be useful for testing cognition in the oldest-old and the impact of aging on cognition in older populations.

Neurocognitive Constructs Underlying Executive Control in Statistically-Determined Mild Cognitive Impairment

BACKGROUND

The model of executive attention proposes that temporal organization, i.e., the time necessary to bring novel tasks to fruition is an important construct that modulates executive control. Subordinate to temporal organization are the constructs of working memory, preparatory set, and inhibitory control.

OBJECTIVE

The current research operationally-defined the constructs underlying the theory of executive attention using intra-component latencies (i.e., reaction times) from a 5-span backward digit test from patients with suspected mild cognitive impairment (MCI).

METHODS

An iPad-version of the Backward Digit Span Test (BDT) was administered to memory clinic patients. Patients with (n = 22) and without (n = 36) MCI were classified. Outcome variables included intra-component latencies for all correct 5-span serial order responses.

RESULTS

Average total time did not differ. A significant 2-group by 5-serial order latency interaction revealed the existence of distinct time epochs. Non-MCI patients produced slower latencies on initial (position 2-working memory/preparatory set) and latter (position 4-inhibitory control) correct serial order responses. By contrast, patients with MCI produced a slower latency for middle serial order responses (i.e., position 3-preparatory set). No group differences were obtained for incorrect 5-span test trials.

CONCLUSION

The analysis of 5-span BDT serial order latencies found distinct epochs regarding how time was allocated in the context of successful test performance. Intra-component latencies obtained from tests assessing mental re-ordering may constitute useful neurocognitive biomarkers for emergent neurodegenerative illness.

A Latent Transition Analysis Model to Assess Change in Cognitive States over Three Occasions: Results from the Rush Memory and Aging Project

BACKGROUND

Conceptualizing cognitive aging as a step-sequential process is useful in identifying particular stages of cognitive function and impairment.

OBJECTIVE

We applied latent transition analysis (LTA) to determine 1) whether the underlying structure of cognitive profiles found at every measurement occasion are uniform across three waves of assessment, 2) whether class-instability is predictive of distal outcomes, and 3) whether class-reversions from impaired to non-impaired using latent modelling is lower than when using clinical criteria of mild cognitive impairment (MCI).

METHODS

A mover-stayer LTA model with dementia as a distal outcome was specified to model transitions of ten neuropsychological measures over three annual waves in the Rush Memory and Aging Project (n = 1,661). The predictive validity of the mover-stayer status for incident Alzheimer's disease (AD) was then assessed.

RESULTS

We identified a five-class model across the three time-points: Mixed-Domain Impairment, Memory-Specific Impairment, Frontal Impairment, Average, and Superior Cognition. None of the individuals in the Impairment classes reverted to the Average or Superior classes. Conventional MCI classification identified 26.4% and 14.1% at Times 1 and 2 as false-positive cases. "Movers" had 87% increased risk of developing dementia compared to those classified as "Stayers".

CONCLUSION

Our findings support the use of latent variable modelling that incorporates comprehensive neuropsychological assessment to identify and classify cognitive impairment.

Executive functions and intelligence from the CHC theory perspective: Investigating the correspondence between the WAIS-IV and the NAB Executive Functions Module

Substantial overlap between executive functions (EFs) and intelligence has been reported. Yet further research is required with respect to how the specific components of the two constructs are interrelated. The present study was aimed at exploring the relationship between EFs and intelligence by examining the latent structure of the Wechsler Adult Intelligence Scale (WAIS-IV) and the Executive Functions Module from the Neuropsychological Assessment Battery (NAB). The aim was also to test the correspondence of the two measures to the Cattell-Horn-Carroll (CHC) theory. 205 healthy participants, aged 18-89 years, were administered the NAB and WAIS-IV. Confirmatory factor analysis (CFA) was employed to explore the latent constructs underlying the two test batteries. Models based on the current WAIS-IV index structure showed worse model fit than models based on the CHC theory. In particular, factors representing broad CHC abilities comprehension knowledge (Gc), fluid reasoning (Gf), visual processing (Gv), processing speed (Gs), and working memory capacity (Gwm) proved model fit improvement. The best model fit, however, provided a five-factor model combining the Gf and Gwm abilities into one factor and additionally including a retrieval fluency (Gr) factor. The results demonstrate strong relationships between the WAIS-IV and the NAB Executive Functions Module and suggest substantial overlap between EFs and intelligence within the CHC framework. Nevertheless, according to the recent update of the CHC theory, the NAB fluency tasks may represent a distinct EF factor comprising Gr abilities independent from the WAIS-IV.

Age-related differences in the predictive ability of executive functions for intelligence

Abstract. The Executive Functions Module of the Neuropsychological Assessment Battery (NAB) and the Wechsler Adult Intelligence Scale – Fourth Edition (WAIS-IV) were used to investigate age-related differences in the predictability of intelligence with executive functions. The NAB subtests age and sex better predicted the WAIS-IV index scales and the Full Scale IQ in the older than in the younger age group, with total variance explained up to 75 % in 60- to 88-year-olds and up to 46 % in 18- to 59-year-olds. The NAB subtests Categories and Word Generation were most frequently included, whereas Letter Fluency was least frequently included in the best-fitting models of WAIS-IV prediction. Mazes predicted better in the younger age group, whereas Judgment predicted better in the older age group.

Assessing the Executive Function Deficits of Patients with Parkinson’s Disease

The aim of the study was to investigate the utility of the Tower of London-Drexel (TOLDX ) in assessing the executive deficits associated with Parkinson’s disease (PD). We sought to determine whether the TOLDX would differentiate between (a) patients with PD and healthy control participants (HCP), (b) demented and nondemented patients, and (c) depressed and nondepressed patients. A new TOLDX score, stimulus bound, was introduced to assess utilization behaviors. Furthermore, the convergent and divergent validity of the TOLDX was examined. The TOLDX total move, rule and time violation, and stimulus-bound scores of patients with PD significantly differed from the HCP. Demented and nondemented patients also differed significantly in their TODX performance, with the stimulus-bound score being the most significantly differentiating score. However, the depressed and nondepressed patients did not differ in their TOLDX performance. Support was found for the convergent and divergent validity of the TOLDX. The clinical and theoretical implications of the findings are discussed.

A culture-brain link: Negative age stereotypes predict Alzheimer's disease biomarkers

Although negative age stereotypes have been found to predict adverse outcomes among older individuals, it was unknown whether the influence of stereotypes extends to brain changes associated with Alzheimer's disease. To consider this possibility, we drew on dementia-free participants, in the Baltimore Longitudinal Study of Aging, whose age stereotypes were assessed decades before yearly magnetic resonance images and brain autopsies were performed. Those holding more-negative age stereotypes earlier in life had significantly steeper hippocampal-volume loss and significantly greater accumulation of neurofibrillary tangles and amyloid plaques, adjusting for relevant covariates. These findings suggest a new pathway to identifying mechanisms and potential interventions related to the pathology of Alzheimer's disease.

Neurocognitive Recovery After Hospital-Treated Deliberate Self-Poisoning With Central Nervous System Depressant Drugs: A Longitudinal Cohort Study

Hospital-treated deliberate self-poisoning (DSP) by central nervous system depressant drugs (CNS-D) has been associated with impairments in cognitive and psychomotor functions at the time of discharge. We aimed to replicate this finding and to compare recovery in the first month after discharge for CNS-D and CNS nondepressant drug ingestions. We also examined a series of multivariate explanatory models of recovery of neurocognitive outcomes over time. The CNS-D group was impaired at discharge compared with the CNS-nondepressant group in cognitive flexibility, cognitive efficiency, and working memory. There were no significant differences at discharge in visual attention, processing speed, visuomotor speed, or inhibition speed. Both groups improved in the latter measures over 1 month of follow-up. However, the CNS-D group's recovery was significantly slower for key neurocognitive domains underlying driving in complex traffic situations, namely, cognitive flexibility, cognitive efficiency, and working memory. Patients discharged after DSP with CNS-D drugs have impairments of some critical cognitive functions that may require up to 1 month to recover. Although more pre- than post-DSP variables were retained as explanatory models of neurocognitive performance overall, recovery over time could not be explained by any one of the measured covariates. Tests of cognitive flexibility could be used in clinical settings as a proxy measure for recovery of driving ability. Regulatory authorities should also consider the implications of these results for the period of nondriving advised after ingestion of CNS-D in overdose. Future research, with adequate sample size, should examine contributions of other variables to the pattern of recovery over time.

The implications of state-dependent tDCS effects in aging: Behavioural response is determined by baseline performance

Young adults typically display a processing advantage towards the left side of space ("pseudoneglect"), possibly as a result of right parietal dominance for spatial attention. This bias is ameliorated with age, with older adults displaying either no strongly lateralised bias, or a slight bias towards the right. This may represent an age-related reduction of right hemispheric dominance and/or increased left hemispheric involvement. Here, we applied anodal transcranial direct current stimulation (atDCS) to the right posterior parietal cortex (PPC; R-atDCS), the left PPC (L-atDCS) and a Sham protocol in young and older adults during a titrated lateralised visual detection task. We aimed to facilitate visual detection sensitivity in the contralateral visual field with both R-atDCS and L-atDCS relative to Sham. We found no differences in the effects of stimulation between young and older adults. Instead the effects of atDCS were state-dependent (i.e. related to task performance at baseline). Relative to Sham, poor task performers were impaired in both visual fields by anodal stimulation of the left posterior parietal cortex (PPC). Conversely, good performers maintained sensitivity in both visual fields in response to R-atDCS, although this effect was small. We highlight the importance of considering baseline task ability when designing tDCS experiments, particularly in older adults.

Test Your Memory (TYM) as a screening instrument in clinical practice - the Polish validation study

OBJECTIVES

The Test Your Memory (TYM) test is a short, self-administered screening cognitive instrument designed for the detection of Alzheimer's disease (AD). The study was aimed to examine the Polish version of TYM as a screening instrument in Polish clinical practice.

METHOD

In this study 199 patients were assessed whereas 131 patients with AD and mild cognitive impairments (MCI) and 94 healthy control subjects took part in the final analysis. The sensitivity and specificity of the TYM test were evaluated among the AD group and healthy control group. The TYM test was compared to other neuropsychological tests, such as Mini-Mental State Examination (MMSE), Clock Drawing Test (CDT), DemTect and Verbal Fluency Test (FAS).

RESULTS

The average TYM score in healthy control group: 45.4, 40.9 in the MCI patients and 23.4 in AD patients. The Polish version of the TYM test showed good correlation with other neuropsychological instruments among AD patients. Participants aged ≥75 and those with primary education performed significantly worse in TYM. The TYM achieved the best differentiation between AD and the healthy control group for ≤39 cut-off with a sensitivity and specificity of 91% and 90%, respectively.

CONCLUSION

The Polish version of the TYM test is a useful instrument and may be seen as an alternative to the MMSE screening test in clinical practice in patients with dementia. However, the normative data suggested that the age and the level of education of the respondents should be considered as important factors affecting the interpretation of the final score.

Differential trajectories of age-related changes in components of executive and memory processes

Several studies have demonstrated age-related declines in general executive function and memory. In this study, we examined cross-sectional and longitudinal age effects in more specific cognitive processes that constitute executive function and memory. We postulated that, whereas some components of executive and memory functions would show age differences and longitudinal declines, other specific abilities would be maintained or even improve with repeated testing. In a sample of individuals ≥55 years old from the Baltimore Longitudinal Study of Aging, we found longitudinal declines in inhibition, manipulation, semantic retrieval, phonological retrieval, switching, and long-term memory over a maximum of 14 years follow-up. In contrast, abstraction, capacity, chunking, discrimination, and short-term memory were maintained or even improved longitudinally, probably due in part to repeated testing. Moreover, whereas several different abilities were correlated across participants' cross-sectional performance, longitudinal changes in performance showed more heterogeneous trajectories. Finally, compared with cross-sectional performance, longitudinal trajectories showed better distinction between participants with and those without later cognitive impairment. These results show that longitudinal cognitive aging of executive and memory functions is not a uniform process but a heterogeneous one and suggest that certain executive and memory functions remain stable despite age-related declines in other component processes.

Memory shaped by age stereotypes over time

OBJECTIVES

Previous studies showed that negative self-stereotypes detrimentally affect the cognitive performance of marginalized group members; however, these findings were confined to short-term experiments. In the present study, we considered whether stereotypes predicted memory over time, which had not been previously examined. We also considered whether self-relevance increased the influence of stereotypes on memory over time.

METHOD

Multiple waves of memory performance were analyzed using individual growth models. The sample consisted of 395 participants in the Baltimore Longitudinal Study of Aging.

RESULTS

Those with more negative age stereotypes demonstrated significantly worse memory performance over 38 years than those with less negative age stereotypes, after adjusting for relevant covariates. The decline in memory performance for those aged 60 and above was 30.2% greater for the more negative age stereotype group than for the less negative age stereotype group. Also, the impact of age stereotypes on memory was significantly greater among those for whom the age stereotypes were self-relevant.

DISCUSSION

This study shows that the adverse influence of negative self-stereotypes on cognitive performance is not limited to a short-term laboratory effect. Rather, the findings demonstrate, for the first time, that stereotypes also predict memory performance over an extended period in the community.

Personality traits prospectively predict verbal fluency in a lifespan sample

In a community-dwelling sample (N = 4,790; age range 14-94), we examined whether personality traits prospectively predicted performance on a verbal fluency task. Open, extraverted, and emotionally stable participants had better verbal fluency. At the facet level, dispositionally happy and self-disciplined participants retrieved more words; those prone to anxiety and depression and those who were deliberative retrieved fewer words. Education moderated the association between conscientiousness and fluency such that participants with lower education performed better on the fluency task if they were also conscientious. Age was not a moderator at the domain level, indicating that the personality-fluency associations were consistent across the life span. A disposition toward emotional vulnerability and being less open, less happy, and undisciplined may be detrimental to cognitive performance.

A canonical correlation analysis of intelligence and executive functioning

Executive functioning is one of the most researched and debated topics in neuropsychology. Although neuropsychologists routinely consider executive functioning and intelligence in their assessment process, more information is needed regarding the relationship between these constructs. This study reports the results of a canonical correlation study between the most widely used measure of adult intelligence, the Wechsler Adult Intelligence Scale, 3rd edition (WAIS-III; Wechsler, 1997), and the Delis-Kaplan Executive Function System (D-KEFS; Delis, Kaplan, & Kramer, 2001). The results suggest that, despite considerable shared variability, the measures of executive functioning maintain unique variance that is not encapsulated in the construct of global intelligence.

Effects of age, gender, education and race on two tests of language ability in community-based older adults

BACKGROUND

Neuropsychological tests, including tests of language ability, are frequently used to differentiate normal from pathological cognitive aging. However, language can be particularly difficult to assess in a standardized manner in cross-cultural studies and in patients from different educational and cultural backgrounds. This study examined the effects of age, gender, education and race on performance of two language tests: the animal fluency task (AFT) and the Indiana University Token Test (IUTT). We report population-based normative data on these tests from two combined ethnically divergent, cognitively normal, representative population samples of older adults.

METHODS

Participants aged > or =65 years from the Monongahela-Youghiogheny Healthy Aging Team (MYHAT) and from the Indianapolis Study of Health and Aging (ISHA) were selected based on (1) a Clinical Dementia Rating (CDR) score of 0; (2) non-missing baseline language test data; and (3) race self-reported as African-American or white. The combined sample (n = 1885) was 28.1% African-American. Multivariate ordinal logistic regression was used to model the effects of demographic characteristics on test scores.

RESULTS

On both language tests, better performance was significantly associated with higher education, younger age, and white race. On the IUTT, better performance was also associated with female gender. We found no significant interactions between age and sex, and between race and education.

CONCLUSIONS

Age and education are more potent variables than are race and gender influencing performance on these language tests. Demographically stratified normative tables for these measures can be used to guide test interpretation and aid clinical diagnosis of impaired cognition.

Oxidative stress and executive function in children receiving chemotherapy for acute lymphoblastic leukemia

BACKGROUND

Neurocognitive sequelae following treatment for pediatric acute lymphoblastic leukemia (ALL) has been reported in a significant proportion of survivors, including those treated only with chemotherapy. Early identification of children "at risk" for neurocognitive problems is not yet reliable. Biomarkers of oxidative stress (e.g., oxidated phosphatidylcholine) in cerebral spinal fluid (CSF) have been correlated with intensity of methotrexate (MTX) treatment, suggesting an association with acute central nervous system toxicity.

PROCEDURE

This study examined the association between oxidized CSF phospholipids and executive functions throughout chemotherapy. Measures of oxidative stress and executive functions were examined in 88 children newly diagnosed with ALL. The children were followed over 3 years with neurocognitive testing and parent ratings of executive functions.

RESULTS

Results demonstrated an association between increased oxidative stress following induction and consolidation and decreased executive function 2 years later. Younger age at diagnosis was associated with both an increase in oxidative stress and in executive dysfunction; younger age was associated with poorer ability to organize materials in one's environment (r(48) = 0.28, P < 0.05) and with greater oxidated phosphatidylcholine in CSF at the end of chemotherapy (r(48) = -0.27, P < 0.05). As such, younger age appears to be the most prominent moderator of neurocognitive decline.

CONCLUSIONS

These results link functional changes to CSF biomarkers and underscore the importance of monitoring cognitive development in young children treated for ALL. Children with less advanced central nervous system development may be particularly vulnerable to the effects of chemotherapy.

Selectivity of executive function deficits in mild cognitive impairment

Impairment in executive cognition (EC) is now recognized as relatively common among older persons with mild cognitive impairment (MCI) and may be predictive of the development of dementia. However, both MCI and executive functioning are broad and heterogeneous constructs. The present study sought to determine whether impairments in specific domains of EC are associated with specific subtypes of MCI. MCI patients (n = 124) were divided into 4 subgroups (amnestic vs. nonamnestic, and single- vs. multiple-domain) on the basis of their performance of widely used neuropsychological screening tests. These patients and 68 normal older persons were administered 18 clinical and experimental tests of executive function. Principal components analysis suggested 2 highly reliable EC components, planning/problem solving and working memory, and a less reliable 3rd component, judgment. Planning/problem solving and working memory, but not judgment, were impaired among the MCI patients. This was true even among those with "pure amnestic" MCI, the least impaired group overall. Multiple-domain MCI patients had more severe impairments in planning/problem solving and working memory than single-domain patients, leading to the supposition that they, not pure amnestic MCIs, are at highest risk of imminent dementia.

Developmental changes in attention tests norms: implications for the structure of attention

Assessment of attention is a key issue in the study of neuropsychological development. In this study we collected Hebrew norms for four frequently used attention tests (Trail Making, Digit-Symbol, Digit Span, and Digit Cancellation), analyzed the developmental sensitivity of each test and traced changes in attention across ages. The tests were administered to 809 boys and girls ranging in age from 8 to 17, divided into 10 age cohorts. The results indicate that, although all tests showed age effects, Digit-Symbol and Digit Cancellation tests were most developmentally sensitive. Another interesting finding was that younger age groups (8-11) are more dissociable by attention tests than older age groups (12-17), indicating that changes in attention are more pronounced in the early years and stabilize in later years.

Normative data for healthy elderly on the phonemic verbal fluency task - FAS

Phonemic verbal fluency tests assess the production of words beginning with specific letters. Of these letters, the most frequently used are F, A and S. It is a sensitive test for assessing frontal lobe functions.

Objective

To provide normative data for the elderly Brazilian population on the FAS test and to investigate the effects of age and schooling on test performance.

Methods

The individuals were divided into three age groups (60-69, 70-79 and =80 years), and into four groups according to education (1-3, 4-7, 8-11 and 12 years). All subjects were assessed by the Mini Mental State Examination and the FAS. Data were analyzed with Student's t test, ANOVA, simple linear regression and Spearman's correlation.

Results

We evaluated 345 cognitively healthy volunteers, 66.66% being female, aged 60 to 93 years, with an educational level ranging from one to 24 years. The average (number of items) ±SD for the whole sample was 28.28±11.53. No significant effect of gender was observed (p=0.5). Performance on the MMSE and education exerted a direct influence on FAS scores (p<0.001), with education being the most significant factor. A positive correlation was found between FAS and the MMSE (r=0.404; p<0.001).

Conclusion

The performance of Brazilian elderly on the phonemic verbal fluency tests-FAS is significantly influenced by education, where individuals with higher educational level present better performance than those with fewer years of schooling. Age and gender did not prove significant with the FAS.

The frontal hypothesis of cognitive aging: factor structure and age effects on four frontal tests among healthy individuals

With 101 healthy aging adult participants, the authors investigated whether executive functions are a unitary concept. The authors established the factor structure of the Wisconsin Card Sorting Test (WCST; E. A. Berg, 1948), the Stroop color and word test (C. J. Golden, 1978), verbal fluency using the Controlled Oral Word Association Test (COWAT; Benton, 1967), and the Digits Backwards subtest of the Wechsler Adult Intelligence Scale-Revised (WAIS-R; D. Wechsler, 1981). The authors also evaluated the extent to which age and other demographic variables predicted common underlying properties of these frontal tests. Results revealed an age-related decline in executive abilities differentially reflected by the selected tasks. These data suggest caution using the COWAT to evaluate executive abilities in older people. The authors interpret findings to support the unitary view of executive abilities and the executive decline proposed by the frontal hypothesis.

Brain activation during mental maze solving

BACKGROUND

So-called Porteus mazes are used to investigate prefrontal cortex (PFC) functioning in normal subjects and patients with different neuropsychiatric disorders. Here we present data confirming the involvement of the PFC for the first time by means of functional magnetic resonance imaging (fMRI). To minimize motor-related activation, mental mazes were used.

METHODS

Mazes as well as pseudo-mazes without any bifurcations were presented to 49 healthy participants during fMRI scans.

RESULTS

Both, mazes as well as pseudo-mazes, activated a large network from visual to parietal regions, reflecting the dorsal stream of visual information processing. Mazes but not pseudo-mazes also activated bilateral areas of the PFC indicating their special role in decision processes. In addition, although no motor response was required during maze performance, both tasks activated subcortical and cortical motor areas.

CONCLUSIONS

These tasks are suitable for investigating and specifying PFC functioning and its impairment in psychiatric disorders such as schizophrenia. In addition, mental mazes might be a suitable task for the investigation of patients with motor disturbances.

Alterations in working memory as a function of leukoaraiosis in dementia

Dementia research suggests executive dysfunction is best understood within the context of disease-specific neuropathology. Leukoaraiosis (LA) results in executive dysfunction yet little is known about its impact on specific aspects of working memory (WM). This study aimed to investigate the relationship between MRI LA severity and WM in dementia. A visual rating scale was used to assign patients with dementia into groups with minimal-mild LA (Low LA; n=34) and moderate-severe LA (High LA; n=32). A modified Digit Span Backward Task consisting of 3-, 4-, and 5-span trials measured specific components of WM. Short-term storage and rehearsal in WM were assessed by the total number of digits reported regardless of recall order (ANY-ORDER; e.g., 47981 recalled '18943', score=4). Mental manipulation in the form of disengagement and temporal re-ordering was assessed by the total number of digits recalled in correct position (SERIAL-ORDER; e.g., 47981 recalled '18943', score=3). There was no difference between LA groups on ANY-ORDER comparisons. The High LA group obtained lower SERIAL-ORDER scores than the Low LA group. Stepwise regression analyses were conducted that first entered MMSE scores then composite z-scores reflecting executive functioning, language and memory. ANY-ORDER performance variance was explained solely by dementia severity. SERIAL-ORDER performance variance was further explained by executive dysfunction. Results suggest that high degrees of LA do not interfere with immediate (digit) recall but do interfere with disengagement and temporal re-ordering. LA may disconnect the frontal lobes from subcortical and cortical structures that form the neuronal networks critical for these WM functions.

Structure of four executive functioning tests in healthy older adults

The authors examined the factor structure of 4 indicators of executive functioning derived from 2 new (i.e., Hayling and Brixton) and 2 traditional (i.e., Stroop and Color Trails) tests. Data were from a cross-sectional sample of 55- to 85-year-old healthy adults (N=427) from the Victoria Longitudinal Study. Confirmatory factor analysis (LISREL 8.52) tested both a 2-factor model of Inhibition (Hayling, Stroop) and Shifting (Brixton, Color Trails) and a single-factor model. The 2-factor model did not fit the data because the covariance matrix of the factors was not positive definite. The single-factor model fit the data well, chi(2)(2, N=427)=0.32, p=.85, root-mean-square error of approximation (RMSEA)=.00, comparative fit index (CFI)=1.00, goodness-of-fit index (GFI)=1.00. Moreover, the single-factor structure of executive functioning was invariant (configural and metric) across gender, and invariant (configural with limited metric) across age. Structural relations showed that poorer executive functioning performance was related to older age and lower fluid intelligence, chi(2)(11, N=418)=23.04, p=.02, RMSEA=.05, CFI=.97, GFI=.98.

Serum cholesterol and cognitive performance in the Framingham Heart Study

OBJECTIVE

The objective of this study was to examine the relationship between total cholesterol (TC) and cognitive performance within the context of the Framingham Heart Study, a large, community-based, prospective investigation of cardiovascular risk factors.

METHODS

Participants were 789 men and 1105 women from the Framingham Heart Study original cohort who were free of dementia and stroke and who received biennial TC determinations over a 16- to 18-year surveillance period. Cognitive tests were administered 4 to 6 years subsequent to the surveillance period and consisted of measures of learning, memory, attention/concentration, abstract reasoning, concept formation, and organizational abilities. Statistical models were adjusted for multiple demographic and biological covariates.

RESULTS

There was a significant positive linear association between TC and measures of verbal fluency, attention/concentration, abstract reasoning, and a composite score measuring multiple cognitive domains. Performance levels for three clinically defined groups were examined. Participants with "desirable" TC levels (<200 mg/dL) performed less well than participants with borderline-high TC levels (200-239 mg/dL) and participants with high TC levels (there exists 240 mg/dL).

CONCLUSIONS

Lower naturally occurring TC levels are associated with poorer performance on cognitive measures, which place high demands on abstract reasoning, attention/concentration, word fluency, and executive functioning.