Spatio-temporal cortical dynamics of phonemic and semantic fluency

Segregated circuits for phonemic and semantic fluency: A novel patient-tailored disconnection study

Phonemic and semantic fluency are neuropsychological tests widely used to assess patients' language and executive abilities and are highly sensitive tests in detecting language deficits in glioma patients. However, the networks that are involved in these tasks could be distinct and suggesting either a frontal (phonemic) or temporal (semantic) involvement. 42 right-handed patients (26 male, mean age = 52.5 years, SD=±13.3) were included in this retrospective study. Patients underwent awake (54.8%) or asleep (45.2%) surgery for low-grade (16.7%) or high-grade-glioma (83.3%) in the frontal (64.3%) or temporal lobe (35.7%) of the left (50%) or right (50%) hemisphere. Pre-operative tractography was reconstructed for each patient, with segmentation of the inferior fronto-occipital fasciculus (IFOF), arcuate fasciculus (AF), uncinate fasciculus (UF), inferior longitudinal fasciculus (ILF), third branch of the superior longitudinal fasciculus (SLF-III), frontal aslant tract (FAT), and cortico-spinal tract (CST). Post-operative percentage of damage and disconnection of each tract, based on the patients' surgical cavities, were correlated with verbal fluencies scores at one week and one month after surgery. Analyses of differences between fluency scores at these timepoints (before surgery, one week and one month after surgery) were performed; lesion-symptom mapping was used to identify the correlation between cortical areas and post-operative scores. Immediately after surgery, a transient impairment of verbal fluency was observed, that improved within a month. Left hemisphere lesions were related to a worse verbal fluency performance, being a damage to the left superior frontal or temporal gyri associated with phonemic or semantic fluency deficit, respectively. At a subcortical level, disconnection analyses revealed that fluency scores were associated to the involvement of the left FAT and the left frontal part of the IFOF for phonemic fluency, and the association was still present one month after surgery. For semantic fluency, the correlation between post-surgery performance emerged for the left AF, UF, ILF and the temporal part of the IFOF, but disappeared at the follow-up. This approach based on the patients' pre-operative tractography, allowed to trace for the first time a dissociation between white matter pathways integrity and verbal fluency after surgery for glioma resection. Our results confirm the involvement of a frontal anterior pathway for phonemic fluency and a ventral temporal pathway for semantic fluency. Finally, our longitudinal results suggest that the frontal executive pathway requires a longer interval to recover compared to the semantic one.

Positive emotion induction improves cardiovascular coping with a cognitive task

Feeling positive emotions seems to favour an adaptive cardiovascular response (greater heart rate variability, HRV), associated with improved cognitive performance. This study aims to test whether the induction of a positive emotional state produce such cardiovascular response and therefore, enhance coping and performance in Tower of Hanoi (ToH). Forty-two Participants were randomly distributed into two groups (Experimental and Control). Experimental group was subjected to the evocation of a memory of success, while control group was subjected to an attentional task before performing ToH. Heart Rate Variability (HRV), activity of the zygomatic major muscle (ZEMG) and emotions were measured. Emotional induction increased ZEMG activity, feelings of emotional valence and HRV, but the performance in ToH was not different from control. Experiencing positive emotions seems to favour an adaptive psychophysiological response when faced with a complex cognitive task. These results are discussed in relation to clinical practice and health.

Abnormal Cortical Activation Patterns Among Chinese-Speaking Schizophrenia Patients During Category and Letter Verbal Fluency Tasks Revealed by Multi-Channel Functional Near-Infrared Spectroscopy

Background: Functional near-infrared spectroscopy (fNIRS) has many advantages over other neuroimaging modalities for routine measurement of task-dependent cortical activation, but most fNIRS studies of schizophrenia have used letter fluency tasks (LFTs). Further, performances on category fluency tasks (CFTs) and LFTs may be distinct in Chinese patients due to the unique semantic features of Chinese written characters. To identify unique disease biomarkers measurable by fNIRS in Chinese schizophrenia patients, this study compared cortical oxygenated hemoglobin changes ([oxy-Hb]) during a Chinese LFT and CFT between patients and healthy controls. Methods: Inpatients of the Second Affiliated Hospital of Xinxiang Medical University were recruited from Match 2020 to July 2021. The Positive and Negative Symptom Scale (PANSS) was used to evaluate psychiatric symptoms. Dynamic changes in [oxy-Hb], an indicator of neural activity, were measured during CFT and LFT performance by 52-channel fNIRS. Results: Forty-seven schizophrenia inpatients and 29 healthy controls completed all tests. Schizophrenia patients showed significant cortical activation at 15 channels covering the left hemisphere and 17 channels over the right hemisphere during the CFT. During the LFT, activity was significantly increased at only six channels, all over the left hemisphere (FDR P < 0.05). In healthy controls, significant [oxy-Hb] increases were found at 24 channels over the left hemisphere and 19 channels over the right hemisphere during CFT. While during the LFT, the significant increases were found at 7 channels all over the left hemisphere (FDR P < 0.05). When years of education was included as a covariate, the schizophrenia group demonstrated no significant hypoactivation relative to healthy controls at any channel after FDR correction (FDR P < 0.05) during CFT while demonstrated significant hypoactivation at channel 11 during LFT (FDR P < 0.05). There were no significant associations between PANSS scores and [oxy-Hb] changes after FDR correction (FDR P < 0.05). Conclusions: Left lateralization during CFT was reduced among schizophrenia patients and may be related to the semantic deficit. The Chinese-CFT could be a more sensitive indicator of frontal-temporal dysfunction in schizophrenia.

A Vector Space Model for Neural Network Functions: Inspirations From Similarities Between the Theory of Connectivity and the Logarithmic Time Course of Word Production

The present report examines the coinciding results of two study groups each presenting a power-of-two function to describe network structures underlying perceptual processes in one case and word production during verbal fluency tasks in the other. The former is theorized as neural cliques organized according to the function N = 2 ⁱ - 1, whereas the latter assumes word conglomerations thinkable as tuples following the function N = 2 ⁱ . Both theories assume the innate optimization of energy efficiency to cause the specific connectivity structure. The vast resemblance between both formulae motivated the development of a common formulation. This was obtained by using a vector space model, in which the configuration of neural cliques or connected words is represented by a N-dimensional state vector. A further analysis of the model showed that the entire time course of word production could be derived using basically one single minimal transformation-matrix. This again seems in line with the principle of maximum energy efficiency.

Electrocorticography reveals spatiotemporal neuronal activation patterns of verbal fluency in patients with epilepsy

Verbal fluency is commonly used to evaluate cognitive dysfunction in a variety of neuropsychiatric diseases, yet the neurobiology underlying performance of this task is incompletely understood. Electrocorticography (ECoG) provides a unique opportunity to investigate temporal activation patterns during cognitive tasks with high spatial and temporal precision. We used ECoG to study high gamma activity (HGA) patterns in patients undergoing presurgical evaluation for intractable epilepsy as they completed an overt, free-recall verbal fluency task. We examined regions demonstrating changes in HGA during specific timeframes relative to speech onset. Early pre-speech high gamma activity was present in left frontal regions during letter fluency and in bifrontal regions during category fluency. During timeframes typically associated with word planning, a distributed network was engaged including left inferior frontal, orbitofrontal and posterior temporal regions. Peri-Rolandic activation was observed during speech onset, and there was post-speech activation in the bilateral posterior superior temporal regions. Based on these observations in the context of prior studies, we propose a model of neocortical activity patterns underlying verbal fluency.

The relationship between voxel-based metrics of resting state functional connectivity and cognitive performance in cognitively healthy elderly adults

In previous studies, resting-state functional connectivity (FC) metrics of specific brain regions or networks based on prior hypotheses have been correlated with cognitive performance. Without constraining our analyses to specific regions or networks, we employed whole-brain voxel-based weighted degree (WD), a measure of local FC strength, to be correlated with three commonly used neuropsychological assessments of language, executive function and memory retrieval in both positive and negative directions in 67 cognitively healthy elderly adults. We also divided voxel-based WD into short-ranged and long-ranged WDs to evaluate the influence of FC distance on the WD-cognition relationship, and performed three validation tests. Our results showed that for language and executive function tests, positive WD correlates were located in the frontal and temporal cortices, and negative WD correlates in the precuneus and occipital cortices; for memory retrieval, positive WD correlates were located in the inferior temporal cortices, and negative WD correlates in the anterior cingulate cortices and supplementary motor areas. An FC-distance-dependent effect was also observed, with the short-ranged WD correlates of language and executive function tests located in the medial brain regions and the long-ranged WD correlates in the lateral regions. Our findings suggest that inter-individual differences in FC at rest are predictive of cognitive ability in the elderly adults. Moreover, the distinct patterns of positive and negative WD correlates of cognitive performance recapitulate the dichotomy between task-activated and task-deactivated neural systems, implying that a competition between distinct neural systems on functional network topology may have cognitive relevance.

Semantic verbal fluency impairment is detectable in patients with subjective cognitive decline

Patients with subjective cognitive decline (SCD) are at higher risk for conversion to dementia due to Alzheimer's disease (AD). Semantic verbal fluency (SVF) seems to be impaired in the early stages of AD. The goal of the present study was to identify the discriminative potential of verbal fluency (VF) in patients with SCD to show if very early signs of cognitive decline may be detected in SCD. We examined 93 normal controls (NC) and 61 participants with SCD. Each participant was administered a comprehensive neuropsychological battery. All participants underwent tests of VF: phonemic verbal fluency (PVF), letters K and P and SVF (animals and vegetables categories). In addition to the total score, two 30-second intervals, and clustering and switching indices in SVF were evaluated. SCD generated fewer words in the total score and 30- to 60-second interval in vegetables category and they performed more switches in animals category. There was no significant difference between the SCD and the NC groups in all other VF measures. Quantitative measures of SVF (a decreased number of vegetables) as well as qualitative measures were detected in SCD group and could be considered as an early neuropsychological marker of subtle cognitive impairment.

Structural connectivity subserving verbal fluency revealed by lesion-behavior mapping in stroke patients

Tests of verbal fluency have been widely used to assess the cognitive functioning of persons, and are typically classified into two categories (semantic and phonological fluency). While widely-distributed divergent and convergent brain regions have been found to be involved in semantic and phonological fluency, the anatomical connectivity underlying the fluency is not well understood. The present study aims to construct a comprehensive white-matter network associated with semantic and phonological fluency by investigating the relationship between the integrity of 22 major tracts in the whole brain and semantic fluency (measured by 3 cues) and phonological fluency (measured by 2 cues) in a group of 51 stroke patients. We found five left-lateralized tracts including the anterior thalamic radiation (ATR), inferior fronto-occipital fasciculus (IFOF), uncinate fasciculus (UF), superior longitudinal fasciculus (SLF) and frontal aslant tract (FAT) were significantly correlated with the scores of both semantic and phonological fluencies. These effects persisted even when we ruled out the influence of potential confounding factors (e.g., total lesion volume). Moreover, the damage to the first three tracts caused additional impairments in the semantic compared to the phonological fluency. These findings reveal the white-matter neuroanatomical connectivity underlying semantic and phonological fluency, and deepen the understanding of the neural network of verbal fluency.

Distinct functional connectivity of the hippocampus during semantic and phonemic fluency

Verbal fluency tasks are typically used in neuropsychological practice for assessment of language function in a variety of neurological disorders. Recently, it has been shown that the hippocampus, a region thought to be exclusive to the domain of memory, is also involved in tests of semantic fluency. The present study further explores hippocampal contribution to verbal fluency using functional Magnetic Resonance Imaging (fMRI) and examining mean activity and inter-regional functional connectivity with known task-related brain regions. Given the clear lateralization of brain areas involved in language, lateralization of hippocampal involvement in semantic and phonemic word fluency was also investigated. Different hippocampal recruitment during semantic and phonemic fluency was found: greater change in activity was seen during semantic fluency, as compared with phonemic fluency. This pattern was obtained in the right and the left hippocampus, with no lateralization effects. Functional connectivity analyses corroborate the notion of selective contribution of the hippocampus to semantic fluency. During the semantic fluency task, connectivity levels between the hippocampi and components of the semantic network did not differ from connectivity levels within the semantic network. In contrast, during the phonemic fluency task, the hippocampi were less correlated with components of the phonemic network, as compared to the within phonemic network connectivity. Importantly, hippocampal connectivity with the semantic network was task-dependent and restricted to periods of semantic fluency performance. Altogether, results suggest that the right and the left hippocampus are integral components of the brain network that selectively supports verbal semantic fluency, but not phonemic fluency.

Language-specific cortical activation patterns for verbal fluency tasks in Japanese as assessed by multichannel functional near-infrared spectroscopy

In Japan, verbal fluency tasks are commonly utilized as a standard paradigm for neuropsychological testing of cognitive and linguistic abilities. The Japanese "letter fluency task" is a mora/letter fluency task based on the phonological and orthographical characteristics of the Japanese language. Whether there are similar activation patterns across languages or a Japanese-specific mora/letter fluency pattern is not certain. We investigated the neural correlates of overt mora/letter and category fluency tasks in healthy Japanese. The category fluency task activated the bilateral fronto-temporal language-related regions with left-superior lateralization, while the mora/letter fluency task led to wider activation including the inferior parietal regions (left and right supramarginal gyrus). Specific bilateral supramarginal activation during the mora/letter fluency task in Japanese was distinct from that of similar letter fluency tasks in syllable-alphabet-based languages: this might be due to the requirement of additional phonological processing and working memory, or due to increased cognitive load in general.

Neuroanatomical correlates of cognitive performance in late life

BACKGROUND/AIM

While a number of studies examined the neuroanatomical correlates of cognitive function in older adults, the results have been inconsistent. Examination of a large epidemiologically acquired sample with high-resolution magnetic resonance imaging has the potential to enhance the evidence in this field.

METHODS

The participants were 326 non-demented elderly adults undergoing a battery of neuropsychological tests and brain magnetic resonance imaging scans. Regression analyses were performed to examine the correlation between voxel-based grey matter (GM) volume and four cognitive domain scores.

RESULTS

Positive correlations were observed between specific GM volumes and cognitive domains, i.e. bilateral temporal lobes and hippocampi with language; bilateral temporal, parietal, and occipital lobes with processing speed; and bilateral frontal, temporal, parietal, and occipital lobes with executive function. The positive correlation between verbal memory performance and GM volume in the bilateral medial temporal lobes was not significant after correction for age.

CONCLUSION

Our findings suggest that the location of GM correlates of cognitive tests is largely consistent with the conventional understanding of the neuroanatomical basis of cognition. However, the lack of hemispheric predominance in these GM correlates, and the extensively positive correlation between GM volume and cognitive performance, perhaps reflects the characteristics of the ageing brain.

Emotion and executive functioning: the effect of normal mood states on fluency tasks

Induced positive affect (PA) can improve verbal fluency performance, and induced negative affect (NA) can increase design fluency performance (Bartolic, Basso, Schefft, Glauser, & Titanic-Schefft, 1999). Building on this, the current study investigated associations between everyday mood states and executive functions. Participants (N = 74, mean age = 51.19 years) completed verbal and design fluency tasks and a self-report affect task. PA was associated with better verbal fluency performance, although NA was not associated with design fluency. Variations in everyday PA may be associated with cognitive performance, whereas greater shifts in NA might be needed to establish associations with executive functioning.

Structural correlates of semantic and phonemic fluency ability in first and second languages

Category and letter fluency tasks are commonly used clinically to investigate the semantic and phonological processes central to speech production, but the neural correlates of these processes are difficult to establish with functional neuroimaging because of the relatively unconstrained nature of the tasks. This study investigated whether differential performance on semantic (category) and phonemic (letter) fluency in neurologically normal participants was reflected in regional gray matter density. The participants were 59 highly proficient speakers of 2 languages. Our findings corroborate the importance of the left inferior temporal cortex in semantic relative to phonemic fluency and show this effect to be the same in a first language (L1) and second language (L2). Additionally, we show that the pre-supplementary motor area (pre-SMA) and head of caudate bilaterally are associated with phonemic more than semantic fluency, and this effect is stronger for L2 than L1 in the caudate nuclei. To further validate these structural results, we reanalyzed previously reported functional data and found that pre-SMA and left caudate activation was higher for phonemic than semantic fluency. On the basis of our findings, we also predict that lesions to the pre-SMA and caudate nuclei may have a greater impact on phonemic than semantic fluency, particularly in L2 speakers.

Atypical functional lateralization of language in autism spectrum disorders

Impaired language is a prominent behavioral marker of autism spectrum disorders (ASD), but its neurobiological underpinnings are incompletely understood. We studied letter and category fluency in 14 high functioning ASD individuals and 14 age-matched controls. Each fluency condition was compared to self-paced repetition of the word "nothing." Responses were recorded to monitor performance. In letter fluency, the ASD group had significantly greater activation than controls in the right frontal and right superior temporal lobes. Between-group differences were not observed in left prefrontal cortex. By examining functional asymmetry in frontal cortex, we found that the ASD group had significantly reduced lateralization of activation patterns in letter fluency compared to the controls. In category fluency, no between-group differences in lateralization were found, in light of greater bilateral activation in controls. These findings indicate reduced hemispheric differentiation for certain verbal fluency tasks in ASD, consistent with some previous evidence of atypical functional and structural asymmetries in autism. Abnormal functional organization may contribute to the language impairment seen in ASD.

Cerebral cortex and the clinical expression of Huntington's disease: complexity and heterogeneity

The clinical phenotype of Huntington's disease (HD) is far more complex and variable than depictions of it as a progressive movement disorder dominated by neostriatal pathology represent. The availability of novel neuro-imaging methods has enabled us to evaluate cerebral cortical changes in HD, which we have found to occur early and to be topographically selective. What is less clear, however, is how these changes influence the clinical expression of the disease. In this study, we used a high-resolution surface based analysis of in vivo MRI data to measure cortical thickness in 33 individuals with HD, spanning the spectrum of disease and 22 age- and sex-matched controls. We found close relationships between specific functional and cognitive measures and topologically specific cortical regions. We also found that distinct motor phenotypes were associated with discrete patterns of cortical thinning. The selective topographical associations of cortical thinning with clinical features of HD suggest that we are not simply correlating global worsening with global cortical degeneration. Our results indicate that cortical involvement contributes to important symptoms, including those that have been ascribed primarily to the striatum, and that topologically selective changes in the cortex might explain much of the clinical heterogeneity found in HD. Additionally, a significant association between regional cortical thinning and total functional capacity, currently the leading primary outcome measure used in neuroprotection trials for HD, establishes cortical MRI morphometry as a potential biomarker of disease progression.

Language related reorganization in adult brain with slow growing glioma: fMRI prospective case-study

One possible mechanism for language plasticity in cases of lesions in left dominant hemisphere is the recruitment of homologous region in the unaffected non-dominant hemisphere. The potential of the right hemisphere to carry out such plasticity is expressed by the functional outcome of patients with lesions in the left hemisphere acquired at childhood prior to language acquisition. Whether lesions in the dominant hemisphere acquired in adulthood can result in functional recovery of language by means of recruitment of the non-dominant hemisphere is undetermined. We describe a 28-year-old, right-handed male diagnosed with a left temporo-frontal glioma. It was decided to manage him expectantly due to the low level of suspicion of malignancy and the close proximity of the lesion to critical language function centers. Language functional MRI (fMRI) tests were performed twice within the ensuing 2 years before surgical intervention. Regional brain activation was measured within the temporal and frontal lobes. Laterality index (LI) was calculated based on the corresponding number of activated voxels. The main finding is that over time, prior to resection of the enlarged tumor, the inferior frontal gyrus (IFG) changed from being strongly left lateralized in the first fMRI exam to being bilateral in the second fMRI exam, mainly due to larger activation in the right hemisphere. By that time, although the patient was not aphasic, his language performance was significantly below average. These findings suggest that a slow growing tumor in an adult language-related area might result in a functional reorganization by recruiting the right hemisphere. However, the contribution of such reorganization to the preservation of language performance remains equivocal.

Differential impairment in semantic, phonemic, and action fluency performance in Friedreich's ataxia: possible evidence of prefrontal dysfunction

This study examined phonemic (letters), semantic (animals) and action verbal fluency cues in twenty-four patients with FRDA, and twenty matched healthy control subjects. The Action Fluency Test (AFT) is a newly-developed verbal fluency cue that consists in asking the subject to rapidly generate verbs. Given the high presence of dysarthria and cognitive slowness in FRDA patients, control tasks were administered in order to dissociate motor/articulatory impairment and cognitive slowness from verbal fluency deficit. Results showed that patients and control subjects performed similarly on the semantic fluency task. In contrast, patients performed significantly poorer on phonemic and action fluency tests. Correlational analyses showed that the deficits cannot be attributed to dysarthria or cognitive slowness. Although executive processes are necessary for initiating and monitoring all verbal fluency tasks, phonemic and action fluency may place a greater burden on strategic processes, given that they require a more unusual type of lexicon search. Thus, the deficits found occur in tasks that require greater executive/prefrontal control. This impairment might be the result of an affectation of cerebellum-prefrontal cortex connections, although the possibility of a primary prefrontal dysfunction remains to be investigated.

Estradiol and tryptophan depletion interact to modulate cognition in menopausal women

Despite an abundance of data in animals, there is little research in humans regarding how estrogen and serotonin (5-HT) may interact to influence cognition. Through the use of estrogen treatment (ET) and tryptophan depletion (TRP-D) in a within-subject design involving healthy menopausal women, we have manipulated both estrogen and 5-HT in order to evaluate their individual and joint effects. Although neither manipulation influenced visuospatial learning, a significant interaction suggested that estrogen exerted a protective effect on verbal memory, such that TRP-D impaired performance to a greater extent before the administration of ET. In consonance with this finding, ET was associated with a small, but positive mood effect on the day following active TRP-D. In addition, ET significantly improved letter-cued verbal fluency with and without TRP-D. Finally, time since last menstrual period was significantly associated with verbal memory scores, such that longer length of hypogonadism resulted in decreased verbal memory performance. These data support the interaction of estrogen and 5-HT in nonreproductive behavior in humans as well as highlight the role of ovarian steroids in cognition.

Functional neuroimaging with MEG: normative language profiles

The reliability of language-specific brain activation profiles was assessed using Magnetoencephalography (MEG) in five experiments involving ninety-seven normal volunteers of both genders ranging in age from seven to eighty-four years. MEG data were analyzed with a fully automated method to eliminate subjective judgments in the process of deriving the activation profiles. Across all experiments, profiles were characterized by significant bilateral activity centered in the superior temporal gyrus, and in activity lateralized to the left middle temporal gyrus. These features were invariant across age, gender, variation in task characteristics, and mode of stimulus presentation. The absolute amount of activation, however, did decline with age in the auditory tasks. Moreover, contrary to the commonly held belief that left hemisphere dominance for language is greater in men than in women, our data revealed an opposite albeit a not consistently significant trend.

The relationship of regional frontal hypometabolism to executive function: a resting fluorodeoxyglucose PET study of patients with epilepsy and healthy controls

Executive dysfunction is common in patients with frontal lobe damage and may depend on the location of pathology within the frontal lobes. However, it is unclear how specific brain regions contribute to different aspects of executive functioning. Eighteen patients with frontal lobe epilepsy, 10 patients with juvenile myoclonic epilepsy, and 14 controls completed a series of tests that measure a broad range of executive functions. Resting fluorodeoxyglucose positron emission tomography scans were collected and regional cerebral rates of glucose uptake values were regressed on test scores. Results revealed that frontal lobe metabolic values were strong predictors of executive functioning in patients with epilepsy, but not in healthy controls. However, nonfrontal regions also contributed unique variance on several measures, suggesting that (1) a network of frontal and nonfrontal regions subserve many executive functions and (2) resting hypometabolism can be a useful predictor of executive dysfunction in patients with epilepsy.