Semantic and letter category naming in Alzheimer's patients: A predictable difference

Neuropsychological impairment in post-COVID condition individuals with and without cognitive complaints

One of the most prevalent symptoms of post-COVID condition is cognitive impairment, which results in a significant degree of disability and low quality of life. In studies with large sample sizes, attention, memory, and executive function were reported as long-term cognitive symptoms. This study aims to describe cognitive dysfunction in large post-COVID condition individuals, compare objective neuropsychological performance in those post-COVID condition individuals with and without cognitive complaints, and identify short cognitive exams that can differentiate individuals with post-COVID symptoms from controls. To address these aims, the Nautilus project was started in June 2021. During the first year, we collected 428 participants' data, including 319 post-COVID and 109 healthy controls (18-65 years old) from those who underwent a comprehensive neuropsychological battery for cognitive assessment. Scores on tests assessing global cognition, learning and long-term memory, processing speed, language and executive functions were significantly worse in the post-COVID condition group than in healthy controls. Montreal Cognitive Assessment, digit symbol test, and phonetic verbal fluency were significant in the binomial logistic regression model and could effectively distinguish patients from controls with good overall sensitivity and accuracy. Neuropsychological test results did not differ between those with and without cognitive complaints. Our research suggests that patients with post-COVID conditions experience significant cognitive impairment and that routine tests like the Montreal Cognitive Assessment, digit symbol, and phonetic verbal fluency test might identify cognitive impairment. Thus, the administration of these tests would be helpful for all patients with post-COVID-19 symptoms, regardless of whether cognitive complaints are present or absent.

STUDY REGISTRATION

www.ClinicalTrials.gov, identifiers NCT05307549 and NCT05307575.

Contribution of Memory Tests to Early Identification of Conversion from Amnestic Mild Cognitive Impairment to Dementia

Background:

Memory tests using controlled encoding and cued recall paradigm (CECR) have been shown to identify prodromal Alzheimer’s disease (AD), but information about the effectiveness of CECR compared to other memory tests in predicting clinical progression is missing.

Objective:

The aim was to examine the predictive ability of a memory test based on the CECR paradigm in comparison to other memory/non-memory tests for conversion to dementia in patients with amnestic mild cognitive impairment (aMCI).

Methods:

270 aMCI patients from the clinical-based Czech Brain Aging Study underwent a comprehensive neuropsychological assessment including the Enhanced Cued Recall test (ECR), a memory test with CECR, two verbal memory tests without controlled encoding: the Auditory Verbal Learning Test (AVLT) and Logical memory test (LM), a visuospatial memory test: the Rey-Osterrieth Complex Figure test, and cognitive testing based on the Uniform Data Set battery. The patients were followed prospectively. Conversion to dementia as a function of cognitive performance was examined using Cox proportional hazard models.

Results:

144 (53%) patients converted to dementia. Most converters (89%) developed dementia due to AD or mixed (AD and vascular) dementia. Comparing the four memory tests, the delayed recall scores on AVLT and LM best predicted conversion to dementia. Adjusted hazard ratios (HR) of immediate recall scores on ECR, AVLT, and LM were similar to the HR of categorical verbal fluency.

Conclusion:

Using the CECR memory paradigm in assessment of aMCI patients has no superiority over verbal and non-verbal memory tests without cued recall in predicting conversion to dementia.

White matter pathways underlying Chinese semantic and phonological fluency in mild cognitive impairment

Neuroimaging evidence has suggested that Chinese-language processing differs from that of its alphabetic-language counterparts. However, the underlying white matter pathway correlations between semantic and phonological fluency in Chinese-language processing remain unknown. Thus, we investigated the differences between two verbal fluency tests on 50 participants with amnestic mild cognitive impairment (aMCI) and 36 healthy controls (HC) with respect to five groups (ventral and dorsal stream fibers, frontal-striatal fibers, hippocampal-related fibers, and the corpus callosum) of white matter microstructural integrity. Diffusion spectrum imaging was used. The results revealed a progressive reduction in advantage in semantic fluency relative to phonological fluency from HC to single-domain aMCI to multidomain aMCI. Common and dissociative white matter correlations between tests of the two types of fluency were identified. Both types of fluency relied on the corpus callosum and ventral stream fibers, semantic fluency relied on the hippocampal-related fibers, and phonological fluency relied on the dorsal stream and frontal-striatal fibers. The involvement of bilateral tracts of interest as well as the association with the corpus callosum indicate the uniqueness of Chinese-language fluency processing. Dynamic associations were noted between white matter tract involvement and performance on the two fluency tests in four time blocks. Overall, our findings suggest the clinical utility of verbal fluency tests in geriatric populations, and they elucidate both task-specific and language-specific brain-behavior associations.

Episodic and Semantic Memory Components of Verbal Paired-Associate Learning

One argument for distinguishing between hard (i.e., low-associate) and easy (i.e., high-associate) paired-associate learning is that hard associates provide a selective measure of episodic memory, whereas easy associates reflect both episodic and semantic memory. This study examined correlations between hard and easy verbal paired associates and episodic and semantic memory in a mixed clinical sample. When age and education were controlled, hard paired associates correlated as much with category fluency (i.e., semantic memory) as they did with immediate recall or retention (i.e., episodic memory). Correlations with hard and easy associates differed more on retention than on immediate recall. Letter fluency was essentially unrelated to either easy or hard associates. The study concludes that hard paired associate learning should not be presumed to selectively measure episodic memory.

Patterns of word-list generation in mild cognitive impairment and Alzheimer's disease

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

Semantic Verbal Fluency in Alzheimer's Disease: Approaches beyond the Traditional Scoring System

This study aimed to expand extant Alzheimer's disease (AD) research on cluster size and switching strategies in semantic verbal fluency (SVF). First, it addressed a significant shortcoming in research, that is, the use of a single semantic category (i.e., Animal). Second, it examined subjects of lower education levels, as research to date has primarily focussed on tertiary education. Subjects were 26 mild to moderate AD patients and 26 healthy elderly, 65 years old and over, with less than 12 years of schooling. The study examined the cluster size and switching variables, together with the number of subcategories, in two semantic categories (i.e., Animal and Supermarket). Furthermore, it investigated the error patterns (i.e., repetitions and categorical errors) across three semantic categories (i.e., Animal, Supermarket and Furniture). The findings provide preliminary support for category-specific effects on qualitative aspects of SVF highlighting the need to incorporate multiple semantic categories to research and clinical practice.

Verbal fluency patterns in amnestic mild cognitive impairment are characteristic of Alzheimer's type dementia

Amnestic mild cognitive impairment (aMCI) represents a high-risk factor for Alzheimer's disease (AD) and is characterized by a selective decline in episodic memory. Although by definition aMCI is not associated with impaired verbal fluency performance, we examined relative differences between fluency tasks because AD is characterized by poorer semantic than phonemic fluency. Phonemic and semantic fluency trials were administered to 46 healthy controls, 33 patients with aMCI, and 33 patients with AD. Results revealed a progressive advantage (controls > aMCI > AD) in semantic, relative to phonemic fluency. Difference scores between tasks distinguished each group from the others with medium to large effect sizes (d) ranging from 0.49 to 1.07. Semantic fluency relies more on semantic associations between category exemplars than does phonemic fluency. This aMCI fluency pattern reflects degradation of semantic networks demonstrating that initial neuropathology may extend beyond known early changes in hippocampal regions.

Category size effects in semantic and letter fluency in Alzheimer's patients

Many studies have found that patients with Alzheimer's disease (AD) perform significantly worse than normal controls on verbal fluency tasks. Moreover, some studies have found that AD patients' deficits compared to controls are more severe for semantic fluency (e.g., vegetables) than for letter fluency (e.g. words that begin with F). These studies, however, have not taken category size into account. A comparison of AD patients and age-matched controls on three semantic and three letter categories revealed that both the size and type of a category significantly predicted AD patients' deficits on verbal fluency tasks. These results suggest that the verbal fluency of AD patients will be most attenuated on large semantic categories.

Letter and category fluency in community-dwelling Canadian seniors: a comparison of normal participants to those with dementia of the Alzheimer or vascular type

Measures of letter (FAS) and category (Animal Naming) fluency were completed by community-dwelling, cognitively normal seniors (n = 635), and by individuals diagnosed with dementia of the Alzheimer type (DAT) (n = 155), or with vascular dementia (n = 39). Among normal seniors, category, but not letter fluency, declined with age, females performed better than males on letter but not on category fluency, and performance increased with education on both tasks. Among participants with DAT, letter fluency was influenced by level of education, whereas category fluency was education-, age-, and gender-invariant. Both measures differentiated normal seniors from those with dementia. Category fluency was more impaired than letter fluency at both mild and moderate stages of dementia, but neither task differentiated DAT from vascular dementia.

Word-list generation deficits in dementia

To evaluate the specificity of the semantic fluency deficit in Alzheimer's disease (AD), we compared the performances of patients with AD, Huntington's disease (HD), vascular dementia (VD), and healthy control subjects on tasks of category (i.e., semantic) and first-letter (i.e., phonemic/lexical) word list generation. As compared to age-appropriate controls, all three patient groups demonstrated relatively more impaired semantic than phonemic fluency. Dementia severity did not affect this relationship. Thus, the greater vulnerability of semantically guided fluency is not specific to AD but occurs in other dementias as well. Deficits in both the organization of semantic memory and retrieval from long-term storage appear to contribute to the relatively poorer performance on semantic than phonemic fluency tasks observed in patients with AD, VD, and HD.

Conversational repair by individuals with dementia of the Alzheimer's type

Conversational repair was examined in videotaped samples of spontaneous mealtime talk of 6 normal elderly adults, 5 subjects with early stage dementia of the Alzheimer's type (EDAT) and 5 subjects with middle stage DAT (MDAT) with a family member who acted as a conversational partner. The overall percentage of utterances involved in communication breakdown and repair and the specific proportions of utterances related to conversation problems, signals identifying problems, and repairs, were evaluated. Using the normal dyads as a control group, results showed the differential effects of DAT onset and progression on the conversational repair behavior of both subjects with DAT and their conversational partner. The percentage of conversation involved in repair was significantly higher for MDAT versus control and EDAT dyads. Despite the increase of conversational troubles with DAT onset and progression, the difficulties were repaired successfully the majority of the time. Subjects with EDAT produced more requests for repair than did their conversational partners. However, conversational partners of EDAT subjects used more elaboration repairs than did EDAT subjects. The opposite pattern was observed in the MDAT group where subjects with MDAT created and repaired more conversational problems than did their conversational partner. MDAT subjects produced more discourse trouble sources than did EDAT subjects. It was also observed that MDAT subjects and conversational partners frequently used nonspecific terms to signal misunderstandings. The findings have important implications for developing family caregiver communication enhancement strategies that are specific to the clinical stage of DAT.

Increased regional cerebral glucose metabolism and semantic memory performance in Alzheimer's disease: a pilot double blind transdermal nicotine positron emission tomography study

Nicotinic receptor dysfunction and impaired semantic memory occur early in Alzheimer's disease patients (AD). Previous research implied that nicotine's ability to enhance alertness, arousal, and cognition in a number of nonclinical populations was a function of its ability to stimulate CNS nicotinic cholinergic receptors. In this study it was hypothesized that transdermal administration of nicotine would increase both regional cerebral glucose metabolism (rCMRglc) and semantic memory (as assessed by verbal fluency). Two mild AD and two elderly controls underwent positron emission tomography scanning during a double blind nicotinic agonist verbal fluency challenge procedure. rCMRglc increases occurred in both AD patients, but not controls. In the two AD patients, verbal fluency scores increased by an average of 17%. One elderly control's verbal fluency increased, and the other decreased. These findings suggest that nicotine's effect on metabolism and verbal fluency is due to its ability to stimulate the cholinergic system.

Generative naming in Parkinson disease patients

The generative naming ability (verbal fluency) of 88 idiopathic Parkinson disease (PD) patients was evaluated and compared to that of 21 Alzheimer disease (AD) patients and 43 normal age- and education-matched normal control subjects. The PD patients were classified according to whether they scored within the normal range on the Mini-Mental State Examination (MMSE), a score of 27 or higher, or in the abnormal range, a score of 26 or lower. Semantic and letter generative naming tasks were administered to assess verbal fluency. Results of the study provide evidence that letter category naming is inherently more difficult than semantic category naming; that age significantly affects generative naming; that PD patients with normal MMSE scores were significantly inferior to normal control subjects in generative naming even after the effects of age and mental status are controlled; that PD patients with non-normal MMSE scores performed like AD patients after controlling for the effects of age and mental status; and, that ideational perseveration is the most common type of error response for all subject groups.