Total output and switching in category fluency successfully discriminates Alzheimer's disease from Mild Cognitive Impairment, but not from frontotemporal dementia

Designing an effective semantic fluency test for early MCI diagnosis with machine learning

Semantic fluency tests are one of the key tests used in batteries for the early detection of Mild Cognitive Impairment (MCI) as the impairment in speech and semantic memory are among the first symptoms, attracting the attention of a large number of studies. Several new semantic categories and variables capable of providing complementary information of clinical interest have been proposed to increase their effectiveness. However, this also extends the time required to complete all tests and get the overall diagnosis. Therefore, there is a need to reduce the number of tests in the batteries and thus the time spent on them while maintaining or increasing their effectiveness. This study used machine learning methods to determine the smallest and most efficient combination of semantic categories and variables to achieve this goal. We utilized a database containing 423 assessments from 141 subjects, with each subject having undergone three assessments spaced approximately one year apart. Subjects were categorized into three diagnostic groups: Healthy (if diagnosed as healthy in all three assessments), stable MCI (consistently diagnosed as MCI), and heterogeneous MCI (when exhibiting alternations between healthy and MCI diagnoses across assessments). We obtained that the most efficient combination to distinguish between these categories of semantic fluency tests included the animals and clothes semantic categories with the variables corrects, switching, clustering, and total clusters. This combination is ideal for scenarios that require a balance between time efficiency and diagnosis capability, such as population-based screenings.

Bidirectional associations of high-level cognitive domains with hand motor function and gait speed in high-functioning older adults: A 7-year study

BACKGROUND

Whether age-related decline in the musculoskeletal system may contribute to a decline in cognitive performance or vice versa is unclear. Understanding the direction of their associations and the extent to which upper and lower extremities similarly predict subtle changes in high-level cognitive performance will help elucidate their mechanisms, especially that of the hand dexterity.

METHODS

We evaluated the bidirectional associations of motor performance and high-level cognitive domains in 165 highly cognitively and physically healthy older adults. Motor performance tests consisted of handgrip strength, hand dexterity, assessed with the Purdue Pegboard Test (PPT), and usual and maximum gait speeds. High-level cognitive measures included executive function and information processing speed. The Trail Making Test (TMT)B and the letter and category fluency tests (LFT and CFT) evaluated executive function, while the TMTA and Digit Symbol assessed processing speed. Measurements were taken at baseline and at 2-, 5- and 7-year follow-up.

RESULTS

Generalized linear mixed-effect models showed that baseline hand dexterity and its trajectory predicted changes in TMTB, CFT, TMTA, and Digit Symbol over time, and vice versa. Baseline maximum gait speed was associated with LFT over time and vice versa. No associations were found for handgrip and usual gait speed.

CONCLUSION

The positive bidirectional association observed both in hand dexterity and maximum gait speed with executive function performance and that of hand dexterity with processing speed over time highlights a reciprocal relationship where each factor affects the other and both factors are dependent on each other, suggesting commonality in their neural basis.

Meta-Analysis of Animal Fluency Performance in Amnestic Mild Cognitive Impairment and Cognitively Unimpaired Older Adults

Animal fluency is a commonly used neuropsychological measure that is used in the diagnosis of amnestic mild cognitive impairment (aMCI) and Alzheimer disease. Although most individuals with aMCI have clinically normal scores on this test, several studies have shown that aMCI individuals' performance is significantly lower than that of cognitively unimpaired (CU) individuals. The aim of this meta-analysis was to characterize the effect size of animal fluency performance differences between aMCI and CU individuals. Literature search with search terms used were: "animal fluency and mild cognitive impairment," "semantic fluency and mild cognitive impairment," "category fluency and mild cognitive impairment." Both the standardized mean difference and the raw mean difference were derived from random effects analyses. Demographically adjusted z-scores for animal fluency performance for the aMCI groups were obtained to determine normative performance. Nineteen studies were included in the analysis. The standardized mean difference for animal fluency performance between CU and aMCI was 0.89 (95% confidence interval: [0.73; 1.04], P <0.001), I2 =70.3% [52.7%; 81.4%], which reflects a large effect size with moderate heterogeneity. The raw mean difference was -4.08 [-4.75; -3.38], P <0.001. The mean animal fluency z-score for aMCI groups was in the Low Average range (z=-0.77). This study found a substantial difference in animal fluency performance between aMCI and CU individuals. The aMCI groups' normative performance did not fall into the impaired range, indicating that there are important subclinical differences in animal fluency performance that may inform the design of cognitive end points for Alzheimer's disease prevention trials.

Learned Irrelevance, Perseveration, and Cognitive Aging: A Cross-Sectional Study of Cognitively Unimpaired Older Adults

The effect of natural aging on physiologic mechanisms that regulate attentional set-shifting represents an area of high interest in the study of cognitive function. In visual discrimination learning, reward contingency changes in categorization tasks impact individual performance, which is constrained by attention-shifting costs. Perseveration (PE) and learned irrelevance (LI) are viewed as two different mechanisms that shape responses to stimuli, which are predicated on the shift in stimulus form. To date, only studies examining patients with Parkinson’s disease have provided some insight into the relationship between individual age and performance in PE and LI tasks. We enrolled 60 healthy individuals (mean [SD] age, 63.0 [12.6]) without a history of dementia, a cerebrovascular incident, or a neurodegenerative disease. No association was observed between crystallized intelligence or verbal fluency scores and reaction time in both PE (r = 0.074, p = 0.603; r = −0.124, p = 0.346) and LI (r = −0.076, p = 0.562; r = −0.081, p = 0.536) task conditions, respectively. In contrast, a statistically significant linear relationship was observed between age and reaction time (RT) for PE (r = 0.259, p = 0.046) but not for LI (r = 0.226, p = 0.083). No significant linear relationship was observed for changing RTs in PE and LI (r = 0.209, p = 0.110). The present study is the first report that provides a descriptive overview of age-related differences in PE and LI in a sample of cognitively unimpaired middle- to older-aged adults.

Verbal fluency tests assess global cognitive status but have limited diagnostic differentiation: evidence from a large-scale examination of six neurodegenerative diseases

Verbal fluency is widely used as a clinical test, but its utility in differentiating between neurodegenerative dementias and progressive aphasias, and from healthy controls, remains unclear. We assessed whether various measures of fluency performance could differentiate between Alzheimer's disease, behavioural variant of frontotemporal dementia, non-fluent and semantic variants of primary progressive aphasia, progressive supranuclear palsy, corticobasal syndrome and healthy controls. Category and letter fluency tasks were administered to 33 controls and 139 patients at their baseline clinical visit. We assessed group differences for total number of words produced, psycholinguistic word properties and associations between production order and exemplar psycholinguistic properties. Receiver operating characteristic curves determined which measure could best discriminate patient groups and controls. The total word count distinguished controls from all patient groups, but neither this measure nor the word properties differentiated the patient groups. Receiver operating characteristic curves revealed that, when comparing controls to patients, the strongest discriminators were total word count followed by word frequency. Word frequency was the strongest discriminator for semantic variant of primary progressive aphasia versus other groups. Fluency word counts were associated with global severity as measured by Addenbrooke's Cognitive Examination Revised. Verbal fluency is an efficient test for assessing global brain-cognitive health but has limited utility in differentiating between cognitively and anatomically disparate patient groups. This outcome is consistent with the fact that verbal fluency requires many different aspects of higher cognition and language.

A simple counting of verbal fluency errors discriminates between normal cognition, mild cognitive impairment and Alzheimer's disease

For this observational cross-sectional study, different modalities of verbal fluency tasks (VFTs) were compared between 143 participants: 35 cognitively healthy controls (CHCs), 71 mild cognitive impairment (MCI) and 37 mild Alzheimer's disease (AD) patients. Binomial logistic regression models were defined to identify VFT variables associated with MCI and AD, with respect to CHC. The results showed that the best errors/repetitions variable associated with MCI and AD was the phonemic task, and with every error the odds of being in the MCI group increased 9.9 times and 12.2 times in AD group, accompanied by high accuracy values (MCI: AUC = 0.824, sensitivity = 0.676, specificity = 0.943; AD: AUC = 0.883, sensitivity = 0.784, specificity = 0.943). The results suggest that, in addition to solely register raw scores, a simple counting of errors and repetitions during VFT can offer valuable clues in detecting MCI and AD, especially in the phonemic task.

Functional Neural Correlates of Semantic Fluency Task Performance in Mild Cognitive Impairment and Alzheimer's Disease: An FDG-PET Study

BACKGROUND

Total score (TS) of semantic verbal fluency test (SVFT) is generally used to interpret results, but it is ambiguous as to specific neural functions it reflects. Different SVFT strategy scores reflecting qualitative aspects are proposed to identify specific cognitive functions to overcome limitations of using the TS.

OBJECTIVE

Functional neural correlates of the TS as well as the other strategy scores in subjects with mild cognitive impairment (MCI) and Alzheimer's disease (AD) dementia using Fluorine-18-Fluorodeoxyglucose positron emission tomography (FDG-PET).

METHODS

Correlations between various SVFT scores (i.e., TS, mean cluster size, switching (SW), hard switching, cluster switching (CSW)) and cerebral glucose metabolism were explored using voxelwise whole-brain approach. Subgroup analyses were also performed based on the diagnosis and investigated the effects of disease severity on the associations.

RESULTS

Significant positive correlation between TS and cerebral glucose metabolism was found in prefrontal, parietal, cingulate, temporal cortex, and subcortical regions. Significantly increased glucose metabolism associated with the SW were found in similar but smaller regions, mainly in the fronto-parieto-temporal regions. CSW was only correlated with the caudate. In the subgroup analysis conducted to assess different contribution of clinical severity, differential associations between the strategy scores and regional glucose metabolism were found.

CONCLUSION

SW and CSW may reflect specific language and executive functions better than the TS. The SVFT is influenced by brain dysfunction due to the progression of AD, as demonstrated by the SW with larger involvement of temporal lobe for the AD, and CSW with significant association only for the MCI.

Brain Dynamics Underlying Cognitive Flexibility Across the Lifespan

The neural mechanisms contributing to flexible cognition and behavior and how they change with development and aging are incompletely understood. The current study explored intrinsic brain dynamics across the lifespan using resting-state fMRI data (n = 601, 6-85 years) and examined the interactions between age and brain dynamics among three neurocognitive networks (midcingulo-insular network, M-CIN; medial frontoparietal network, M-FPN; and lateral frontoparietal network, L-FPN) in relation to behavioral measures of cognitive flexibility. Hierarchical multiple regression analysis revealed brain dynamics among a brain state characterized by co-activation of the L-FPN and M-FPN, and brain state transitions, moderated the relationship between quadratic effects of age and cognitive flexibility as measured by scores on the Delis-Kaplan Executive Function System (D-KEFS) test. Furthermore, simple slope analyses of significant interactions revealed children and older adults were more likely to exhibit brain dynamic patterns associated with poorer cognitive flexibility compared with younger adults. Our findings link changes in cognitive flexibility observed with age with the underlying brain dynamics supporting these changes. Preventative and intervention measures should prioritize targeting these networks with cognitive flexibility training to promote optimal outcomes across the lifespan.

Striking loss of second language in bilingual patients with semantic dementia

BACKGROUND

Studies of bilingual or multilingual patients with neurodegenerative diseases that disrupt language like the primary progressive aphasias (PPA) may contribute valuable information on language organization in the bilingual brain and on the factors affecting language decline. There is limited literature on bilingual PPA and in particular on semantic dementia, a type of PPA with selective loss of semantic memory. We studied the nature and severity of naming and comprehension deficits across languages in bilingual patients with semantic dementia (SD).

METHODS

Sixteen bilingual patients with SD and 34 bilingual age-matched controls were administered the modified Boston Naming Test and components of Cambridge Semantic Battery. The patients' performance on picture naming and word comprehension was compared across languages and with controls. The most proficient language on self-rating was labelled as L1 and less proficient as L2.

RESULTS

We observed striking loss of second language (L2) in SD for both receptive and expressive language, even in patients who were premorbidly fluent in their L2. Naming and comprehension in every patient's L2 were impaired relative to both their own first-language (L1) scores and controls' L2 scores. Furthermore, item-specific correct responses in each patient's L2 were a subset of their successes in L1.

DISCUSSION

A striking contrast in performance between two languages in bilingual patients with SD indicates that a bilingual's L2 or less proficient language is more vulnerable to neurodegeneration. Our findings also support a common semantic network in the brain for the different languages of bilinguals.

Quanti-qualitative components of the semantic verbal fluency test in cognitively healthy controls, mild cognitive impairment, and dementia subtypes

This study is aimed to evaluating the underlying cognitive strategies used during Semantic Verbal Fluency (SVF) performance and comparing the differences between cognitively healthy controls (CHC), amnestic and amnestic-multiple domain mild cognitive impairment (a-MCI and a-md-MCI), Alzheimer's disease (AD), Lewy body dementia (LBD), and behavioral variant frontotemporal dementia (bvFTD). The cross-sectional study comprised 236 participants involving 78 CHC individuals, 33 a-MCI and 48 a-md-MCI, 39 AD, 22 LBD, and 16 bvFTD patients. Scores differed significantly when comparing CHC with dementia groups, showing medium to large variances. The best components in distinguishing between CHC and the dementia groups were the SVF-Total score and SVF-Cluster Size variables. CHC showed different performance in the SVF-Cluster Size variable compared with a-md-MCI, AD, and bvFTD; whereas, in the SVF-Mean Cluster Size, CHC differed from MCI's, AD, and LBD. The switching component displayed smaller capacity to differentiate between the clinical groups. The effect size was large comparing AD with bvFTD (1.267) and medium comparing AD with LBD (0.689) using the SVF-Cluster Size variable, but small using the other variables for the comparisons between dementia groups. Quanti-qualitative examination of the SVF may provide a valuable clue in distinguishing CHC from MCI and different dementia subtypes.