Neural processing of overt word generation in healthy individuals: the effect of age and word knowledge

Electrical stimulation of the cerebellum facilitates automatic but not controlled word retrieval

Recent research has indicated that the cerebellum is engaged in language functions, yet the role of the cerebellum in lexical-semantic memory is poorly understood. In a double-blind randomized controlled experiment, we therefore targeted the cerebellum by transcranial direct current stimulation (tDCS) to assess and compare the contribution of the cerebellar processing to automatic and controlled retrieval of words in healthy adults (n = 136). Anodal cerebellar tDCS facilitated retrieval of semantically related words in free-associative chains, which was not due to a non-specific acceleration of processing speed. The stimulation had no influence on controlled word retrieval that employed inhibition or switching. The effect of cathodal tDCS was opposite to the anodal stimulation, but statistically non-significant. Our data show that the cerebellum is engaged extracting associative information from the system of semantic representations, established and strengthened/automated by learning, and indicates a domain-general role of this structure in automation of behavior, cognition and language.

Effects of age, gender, and education on task performance and prefrontal cortex processing during emotional and non-emotional verbal fluency tests

The emotional semantic fluency test (SFT) is an emerging verbal fluency test that requires controlled access to emotional lexical information. Currently, how demographic variables influence neurocognitive processing during this test remains elusive. The present study compared the effects of age, gender, and education on task performance and prefrontal cortex (PFC) processing during the non-emotional and emotional SFTs. One-hundred and thirty-three Cantonese-speaking adults aged 18-79 performed the non-emotional and emotional SFTs while their PFC activation was measured using functional near-infrared spectroscopy. Results showed that more education predicted better non-emotional SFT performance, whereas younger age, being female, and more education predicted better emotional SFT performance. Only age significantly affected PFC activation during the SFTs, and the effect was comparable between the two SFTs. Thus, compared with its non-emotional analog, the emotional SFT is influenced by overlapping yet distinct demographic variables. There is a similar age-related reorganization of PFC function across SFT performances.

Resting State Network Segregation Modulates Age-Related Differences in Language Production

Older adults typically exhibit decline in language production. However, how the brain supports or fails to support these processes is unclear. Moreover, there are competing hypotheses about the nature of age-related neural changes and whether age-related increases in neural activity reflect compensation or a decline in neural efficiency. In the current study, we investigated the neural bases of language production focusing on resting state functional connectivity. We hypothesized that language production performance, functional connectivity, and their relationship would differ as a function of age. Consistent with prior work, older age was associated with worse language production performance. Functional connectivity analyses showed that network segregation within the left hemisphere language network was maintained across adulthood. However, increased age was associated with lower whole brain network segregation. Moreover, network segregation was related to language production ability. In both network analyses, there were significant interactions with age-higher network segregation was associated with better language production abilities for younger and middle-aged adults, but not for older adults. Interestingly, there was a stronger relationship between language production and the whole brain network segregation than between production and the language network. These results highlight the utility of network segregation measures as an index of brain function, with higher network segregation associated with better language production ability. Moreover, these results are consistent with stability in the left hemisphere language network across adulthood and suggest that dedifferentiation among brain networks, outside of the language network, is a hallmark of aging and may contribute to age-related language production difficulties.

Task difficulty modulates age-related differences in functional connectivity during word production

Older adults typically report increased difficulty with language production, while its neural bases are less clear. The current study investigated the neural bases of age-related differences in language production at the word level and the modulating effect of task difficulty, focusing on task-based functional connectivity. Using an English phonological Go/No-Go picture naming task, task difficulty was manipulated by varying the proportion of naming trials (Go trials) and inhibition trials (No-Go trials) across runs. Behaviorally, compared to younger adults, older adults performed worse, and showed larger effects of task difficulty. Neurally, older adults had lower within language network connectivity compared to younger adults. Moreover, older adults' language network became less segregated as task difficulty increased. These results are consistent with the Compensation-Related Utilization of Neural Circuits Hypothesis, suggesting that the brain becomes less specified and efficient with increased task difficulty, and that these effects are stronger among older adults (i.e., more dedifferentiated).

Semantic fluency reveals reduced functional connectivity between subcategorical co-hyponyms in recent-onset inpatients with first-episode psychosis

Data on clustering and switching during semantic fluency (SF) in patients with first-episode psychosis (PwFEP) are scant. We aimed to investigate (1) clustering and switching on SF in PwFEP using more detailed clustering analyses and (2) the possibility of disproportionate clustering deficits across different SF tasks in PwFEP and healthy subjects (HS), with the latter being suggested by the current literature on patients with schizophrenia. We recruited 22 Croatian-speaking PwFEP with schizophrenia features or symptoms and 22 HS matched in age, sex distribution, and handedness. All patients were medicated and had a mean illness duration of 1 month. The categories animals, trees, vegetables, fruits, and musical instruments were administered for SF. PwFEP produced significantly fewer correct words in the aggregate score, as well as across all categories. The switching rate was significantly higher in PwFEP, but no post hoc comparisons were significant. PwFEP also produced significantly smaller clusters, yet the post hoc comparisons for the tree and fruit task were not significant. A higher switching rate and smaller clusters indicate less efficient functional connectivity within subcategories of the given categories, but not necessarily between the subcategories. Although both less likely to produce a cluster once a switch has been uttered and less likely to produce clusters larger than two words compared to HS, the latter deficit was more pronounced. Our results further suggest that PwFEP might show normal clustering performance on some SF tasks. We discuss the results in the context of the hypothesis of semantic hyperactivation in psychoses.

Neural Resources Supporting Language Production vs. Comprehension in Chronic Post-stroke Aphasia: A Meta-Analysis Using Activation Likelihood Estimates

In post-stroke aphasia, language tasks recruit a combination of residual regions within the canonical language network, as well as regions outside of it in the left and right hemispheres. However, there is a lack of consensus as to how the neural resources engaged by language production and comprehension following a left hemisphere stroke differ from one another and from controls. The present meta-analysis used activation likelihood estimates to aggregate across 44 published fMRI and PET studies to characterize the functional reorganization patterns for expressive and receptive language processes in persons with chronic post-stroke aphasia (PWA). Our results in part replicate previous meta-analyses: we find that PWA activate residual regions within the left lateralized language network, regardless of task. Our results extend this work to show differential recruitment of the left and right hemispheres during language production and comprehension in PWA. First, we find that PWA engage left perilesional regions during language comprehension, and that the extent of this activation is likely driven by stimulus type and domain-general cognitive resources needed for task completion. In contrast to comprehension, language production was associated with activation of the right frontal and temporal cortices. Further analyses linked right hemisphere regions involved in motor speech planning for language production with successful naming in PWA, while unsuccessful naming was associated with the engagement of the right inferior frontal gyrus, a region often implicated in domain-general cognitive processes. While the within-group findings indicate that the engagement of the right hemisphere during language tasks in post-stroke aphasia differs for expressive vs. receptive tasks, the overall lack of major between-group differences between PWA and controls implies that PWA rely on similar cognitive-linguistic resources for language as controls. However, more studies are needed that report coordinates for PWA and controls completing the same tasks in order for future meta-analyses to characterize how aphasia affects the neural resources engaged during language, particularly for specific tasks and as a function of behavioral performance.

Age-Dependent Contribution of Domain-General Networks to Semantic Cognition

Aging is characterized by a decline of cognitive control. In semantic cognition, this leads to the paradox that older adults usually show poorer task performance than young adults despite their greater semantic knowledge. So far, the underlying neural changes of these behavioral differences are poorly understood. In the current neuroimaging study, we investigated the interaction of domain-specific and domain-general networks during verbal semantic fluency in young and older adults. Across age groups, task processing was characterized by a strong positive integration within the multiple-demand as well as between the multiple-demand and the default mode network during semantic fluency. However, the behavioral relevance of strengthened connectivity differed between groups: While within-network functional connectivity in both networks predicted greater efficiency in semantic fluency in young adults, it was associated with slower performance in older adults. Moreover, only young adults profited from connectivity between networks for their semantic memory performance. Our results suggest that the functional coupling of usually anticorrelated networks is critical for successful task processing, independent of age, when access to semantic memory is required. Furthermore, our findings lend novel support to the notion of reduced efficiency in the aging brain due to neural dedifferentiation in semantic cognition.

The intensity and connectivity of spontaneous brain activity in a language network relate to aging and language

Neuroimaging studies often either look at functional activation in response to an explicit task, or functional connectivity (i.e., interregional correlations) during resting-state. Few studies have looked at the intensity of brain activity or its relationship with age, behavior, and language. The current study investigated both intensity (i.e., the Amplitude of Low-Frequency Fluctuations, ALFF) and the functional connectivity of spontaneous brain activity during rest and their relationship with age and language. A life-span sample of individuals (N = 152) completed a battery of neuropsychological tests to assess basic cognitive functions and resting-state functional MRI data to assess spontaneous brain activity. Focusing on an extend language network, the mean ALFF and total degree were calculated for this network. We found that increased age was associated with more intense activity (i.e., higher ALFF) but lower within-network connectivity. Additionally, these increases in activity within the language network during resting-state were related to worse language ability, particularly in younger adults, supporting a dedifferentiation account of cognition. Our results support the utility of using resting-state data as an indicator of cognition and support the role of ALFF as a potential biomarker in characterizing the relationships between resting-state brain activity, age, and cognition.

Patient Competency Rating Scale-Brazilian Revised Version (PCRS-R-BR): Normative and Psychometric Data in 154 Healthy Individuals

Background Patient Competency Rating Scale (PCRS-R-BR) is a clinical tool to evaluate the degree of competence in cognitive skills perceived by patients with brain injuries. However, no studies have investigated the influence of sociodemographic variables on self-report and self-awareness of healthy individuals.Aim This study aimed to (1) present normative data from the PCRS-R-BR in a healthy adult Brazilian sample; and (2) investigate psychometric properties of the scaleMethod One hundred and fifty-four adults that were divided in three age groups and two education groups and their informants completed the PCRS-R-BR.Results Score on the PCRS-R-BR Patient's Form differed as a function of age with younger adults reporting less competency than older individuals. An education effect was found on Attention/Working memory Factor on the Informant's PCRS-R-BR with informants of higher education adults reporting better competency than lower education individuals. A gender effect was observed on the Informant's Form. The Informant's Form scores of informants of women were higher than the scores provided by the informants of men. PCRS-R-BR showed adequate consistency coefficients and six factors.Conclusion PCRS-R-BR scores showed acceptable validity evidence and provides information regarding how age and gender effects may influence ratings in a Brazilian sample.

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.

Chasing language through the brain: Successive parallel networks

OBJECTIVE

To describe the spatio-temporal dynamics and interactions during linguistic and memory tasks.

METHODS

Event-related electrocorticographic (ECoG) spectral patterns obtained during cognitive tasks from 26 epilepsy patients (aged: 9-60 y) were analyzed in order to examine the spatio-temporal patterns of activation of cortical language areas. ECoGs (1024 Hz/channel) were recorded from 1567 subdural electrodes and 510 depth electrodes chronically implanted over or within the frontal, parietal, occipital and/or temporal lobes as part of their surgical work-up for intractable seizures. Six language/memory tasks were performed, which required responding verbally to auditory or visual word stimuli. Detailed analysis of electrode locations allowed combining results across patients.

RESULTS

Transient increases in induced ECoG gamma power (70-100 Hz) were observed in response to hearing words (central superior temporal gyrus), reading text and naming pictures (occipital and fusiform cortex) and speaking (pre-central, post-central and sub-central cortex).

CONCLUSIONS

Between these activations there was widespread spatial divergence followed by convergence of gamma activity that reliably identified cortical areas associated with task-specific processes.

SIGNIFICANCE

The combined dataset supports the concept of functionally-specific locally parallel language networks that are widely distributed, partially interacting in succession to serve the cognitive and behavioral demands of the tasks.

The Role of Moderating Variables on BOLD fMRI Response During Semantic Verbal Fluency and Finger Tapping in Active and Educated Healthy Seniors

Semantic verbal fluency is among the most employed tasks in cognitive aging research and substantial work is devoted to understanding the underlying mechanisms behind age-related differences at the neural and behavioral levels. The present investigation aimed to evaluate the role of moderating variables, such as age, sex, MMSE, and proxies of cognitive reserve (CR) on the hemodynamic response evoked by semantic verbal fluency in healthy young and healthy older adults. So far, no study has been conducted to this end. To elucidate the exclusive effect of the mentioned variables on brain activation during semantic fluency, finger tapping was included as a control task. Results showed that disregarding adjustments for age, older adults displayed important parietal activations during semantic fluency as well as during finger-tapping. Specifically, the anterior intra-parietal sulcus (IPS) and left inferior parietal lobule (IPL) were areas activated in both tasks in the older group. Younger adults, only displayed parietal activations related to age and sex when these demographics were employed as predictors. Concerning proxies of CR in semantic fluency, the only vocabulary was an important moderator in both age groups. Higher vocabulary scores were associated with lesser activation in occipital areas. Education did not show significant correlations with brain activity during semantic fluency in any of the groups. However, both CR proxies were significantly correlated to brain activations of older adults during finger tapping. Specifically, vocabulary was associated with frontal regions, while education correlated with parietal lobe and cingulate gyrus. Finally, the effects of MMSE were mostly observed on brain activation of older adults in both tasks. These findings demonstrate that the effects of moderating variables on shaping brain activation are intricate and not exclusive of complex verbal tasks. Thus, before adjusting for “nuisance variables,” their importance needs to be established. This is especially true for samples including older adults for whom a motor task may be a demanding operation due to normal age-related processes of dedifferentiation.

Association Between White Matter Microstructure and Verbal Fluency in Patients With Multiple Sclerosis

Verbal fluency refers to the ability to generate words quickly and efficiently according to predefined phonological or semantic criteria. Deficits in verbal fluency limit patients' ability to communicate effectively and to function well in social setups. Multiple sclerosis (MS) patients suffer from various cognitive impairments, and some of them experience language deficits as well. The goal of this study is to examine the contribution of the dorsal and ventral language pathways to verbal fluency in MS patients. All patients (N = 33) underwent diffusion MRI (dMRI) and fluency measurements. Diffusion parameters were calculated along dorsal and ventral language-related pathways and their right-hemispheric homologs, identified individually in each patient. Significant correlations were found between fluency measures and mean fractional anisotropy (FA) in several pathways, including the left fronto-temporal arcuate fasciculus (AFft), bilateral inferior fronto-occipital fasciculus (IFOF), and bilateral frontal aslant tract. Along-tract correlations revealed a more selective pattern of associations: letter-based fluency was associated with FA in a segment of the left AFft (dorsal pathway), while category-based fluency was associated with FA in a segment of the right IFOF (ventral pathway). The observed pattern of associations, mapping letter-based fluency to the dorsal stream and category-based fluency to the ventral stream, fits well within the dual stream framework of language processing. Further studies will be necessary to assess whether these associations generalize to the typical adult population or whether they are tied to the clinical state.

More expertise for a better perspective: Task and strategy-driven adaptive neurofunctional reorganization for word production in high-performing older adults

The suggestion that neurofunctional reorganization may contribute to preserved language abilities is still emerging in aging studies. Some of these abilities, such as verbal fluency (VF), are not unitary but instead rely on different strategic processes that are differentially changed with age. Younger (n = 13) and older adults (n = 13) carried out an overt self-paced semantic and orthographic VF tasks within mixed fMRI design. Our results suggest that patterns of brain activation sustaining equivalent performances could be underpinned by different strategies facing brain changes during healthy aging. These main findings suggest that temporally mediated semantic clustering and frontally mediated orthographic switching were driven by evolutive neurofunctional resources in high-performing older adults. These age-related activation changes can appear to be compatible with the idea that unique neural patterns expressing distinctive cognitive strategies are necessary to support older adults' performance on VF tasks.

Functional topography of the human cerebellum

Accumulating evidence points to a critical role for the human cerebellum in both motor and nonmotor behaviors. A core tenet of this new understanding of cerebellar function is the existence of functional subregions within the cerebellum that differentially support motor, cognitive, and affective behaviors. This cerebellar functional topography - based on converging evidence from neuroanatomic, neuroimaging, and clinical studies - is evident in both adult and pediatric populations. The sensorimotor homunculi in the anterior lobe and lobule VIII established in early tract tracing and electrophysiologic studies are evident in both task-based and resting-state human functional imaging studies. In patients, damage to the anterior cerebellum, extending into medial lobule VI, is associated with the cerebellar motor syndrome. The cerebellar posterior lobe, including vermal and hemispheric regions of lobules VI and VII, is reciprocally interconnected with cerebral association and paralimbic cortices. Resting-state and task-based neuroimaging studies show functional activation patterns in these regions during higher-level cognitive tasks, and lesions of the posterior cerebellum lead to the cerebellar cognitive affective/Schmahmann syndrome with its characteristic intellectual and emotional impairments. The existence of cerebellar connectional and functional topography provides the critical anatomic substrate for a cerebellar role in both motor and nonmotor functions. It also establishes a framework for interpreting cerebellar activation patterns, cognitive and behavioral outcomes following cerebellar damage, and the cerebellar structural and functional differences reported in a range of neurodevelopmental and neuropsychiatric disorders.

The Effects of Home-Based Cognitive Training on Verbal Working Memory and Language Comprehension in Older Adulthood

Effective language understanding is crucial to maintaining cognitive abilities and learning new information through adulthood. However, age-related declines in working memory (WM) have a robust negative influence on multiple aspects of language comprehension and use, potentially limiting communicative competence. In the current study (N = 41), we examined the effects of a novel home-based computerized cognitive training program targeting verbal WM on changes in verbal WM and language comprehension in healthy older adults relative to an active component-control group. Participants in the WM training group showed non-linear improvements in performance on trained verbal WM tasks. Relative to the active control group, WM training participants also showed improvements on untrained verbal WM tasks and selective improvements across untrained dimensions of language, including sentence memory, verbal fluency, and comprehension of syntactically ambiguous sentences. Though the current study is preliminary in nature, it does provide initial promising evidence that WM training may influence components of language comprehension in adulthood and suggests that home-based training of WM may be a viable option for probing the scope and limits of cognitive plasticity in older adults.

Distinct Neuropsychological Correlates in Positive and Negative Formal Thought Disorder Syndromes: The Thought and Language Disorder Scale in Endogenous Psychoses

The correlation of formal thought disorder (FTD) symptoms and subsyndromes with neuropsychological dimensions is as yet unclear. Evidence for a dysexecutive syndrome and semantic access impairments has been discussed in positive FTD, albeit focusing mostly on patients with schizophrenia. We investigated the correlation of the full range of positive and negative as well as subjective and objective FTD with neuropsychological domains in different patient groups. Patients with ICD-10 schizophrenia (n = 51), depression (n = 51), and bipolar mania (n = 18), as well as healthy subjects (n = 60), were interviewed with the Rating Scale for the Assessment of Objective and Subjective Formal Thought and Language Disorder (TALD) and assessed using a multidimensional neuropsychological test battery (executive function, semantic and lexical verbal fluency, attention, working memory, and abstract thinking). Partial correlation analysis, controlling for age and word knowledge, revealed significant results for the objective positive FTD dimension and executive dysfunctions. Objective negative FTD was associated with deficits in lexico-semantic retrieval, as well as attention and working memory dysfunctions. The results suggest that different neuropsychological substrates correlate with the multidimensional and phenomenologically different FTD syndromes. FTD is a complex, multidimensional syndrome with a variety of neuropsychological impairments, which should be accounted for in future studies investigating the pathogenesis of FTD.

Age-related differences in resolving semantic and phonological competition during receptive language tasks

Receptive language (e.g., reading) is largely preserved in the aging brain, and semantic processes in particular may continue to develop throughout the lifespan. We investigated the neural underpinnings of phonological and semantic retrieval in older and younger adults during receptive language tasks (rhyme and semantic similarity judgments). In particular, we were interested in the role of competition on language retrieval and varied the similarities between a cue, target, and distractor that were hypothesized to affect the mental process of competition. Behaviorally, all participants responded faster and more accurately during the rhyme task compared to the semantic task. Moreover, older adults demonstrated higher response accuracy than younger adults during the semantic task. Although there were no overall age-related differences in the neuroimaging results, an Age×Task interaction was found in left inferior frontal gyrus (IFG), with older adults producing greater activation than younger adults during the semantic condition. These results suggest that at lower levels of task difficulty, older and younger adults engaged similar neural networks that benefited behavioral performance. As task difficulty increased during the semantic task, older adults relied more heavily on largely left hemisphere language regions, as well as regions involved in perception and internal monitoring. Our results are consistent with the stability of language comprehension across the adult lifespan and illustrate how the preservation of semantic representations with aging may influence performance under conditions of increased task difficulty.

The neural language systems that support healthy aging: Integrating function, structure, and behavior

Although healthy aging is generally characterized by declines in both brain structure and function, there is variability in the extent to which these changes result in observable cognitive decline. Specific to language, age-related differences in language production are observed more frequently than in language comprehension, although both are associated with increased right prefrontal cortex activation in older adults. The current paper explores these differences in the language system, integrating them with theories of behavioral and neural cognitive aging. Overall, data indicate that frontal reorganization of the dorsal language stream in older adults benefits task performance during comprehension, but not always during production. We interpret these results in the CRUNCH framework (compensation-related utilization of neural circuits hypothesis), which suggests that differences in task and process difficulty may underlie older adults' ability to successfully adapt. That is, older adults may be able to neurally adapt to less difficult tasks (i.e., comprehension), but fail to do so successfully as difficulty increases (i.e., production). We hypothesize greater age-related differences in aspects of language that rely more heavily on the dorsal language stream (e.g., syntax and production) and that recruit general cognitive resources that rely on frontal regions (e.g., executive function, working memory, inhibition). Moreover, there should be a relative sparing of tasks that rely predominantly on ventral stream regions. These results are both consistent with patterns of age-related structural decline and retention and with varying levels of difficulty across comprehension and production. This neurocognitive framework for understanding age-related differences in the language system centers on the interaction between prefrontal cortex activation, structural integrity, and task difficulty.

Neuroanatomical correlates of verbal fluency in early Alzheimer's disease and normal aging

Verbal fluency (VF) impairments occur early in Alzheimer's disease (AD) and to a lesser extent also in normal aging. However, the neural underpinnings of these impairments are not fully understood. The present study evaluated whether VF impairments in early AD and normal aging rely upon common or different neuroanatomical correlates. We examined the association between VF performance and brain structure in 18 mild AD patients and 24 healthy elderly. Linear regressions were performed between accuracy and time intervals in VF scores and structural measurements of cerebral gray matter (GM) and white matter (WM) using MRI. Results showed that semantic VF correlated exclusively with GM in cerebellum, left temporal fusiform cortex, and WM in uncinate fasciculus, inferior fronto-occipital fasciculus and corpus callosum. Phonemic VF showed unique associations between intervals and WM in left-hemisphere tracts. The association between GM in hippocampus, subcortical structures and semantic accuracy differentiated patients from controls. Results showed that VF impairments are primarily associated with same structural brain changes in AD as in healthy elderly but at exaggerated levels. However, specific VF deficiencies and their underlying neural correlates exist and these clearly differentiate the initial stages of AD.

Older but still fluent? Insights from the intrinsically active baseline configuration of the aging brain using a data driven graph-theoretical approach

A major part of our knowledge about the functioning of the aging brain comes from task-induced activation paradigms. However, the aging brain's intrinsic functional organization may be already a limiting factor for the outcome of an actual behavior. In order to get a better understanding of how this functional baseline configuration of the aging brain may affect cognitive performance, we analyzed task-free fMRI data of older 186 participants (mean age=70.4, 97 female) and their performance data in verbal fluency: First, we conducted an intrinsic connectivity contrast analysis (ICC) for the purpose of evaluating the brain regions whose degree of connectedness was significantly correlated with fluency performance. Secondly, using connectivity analyses we investigated how the clusters from the ICC functionally related to the other major resting-state networks. Apart from the importance of intact fronto-parietal long-range connections, the preserved capacity of the DMN for a finely attuned interaction with the executive-control network and the language network seems to be crucial for successful verbal fluency performance in older people. We provide further evidence that the right frontal regions might be more prominently affected by age-related decline.

Neural differences between monolinguals and early bilinguals in their native language during comprehension

Research has shown that semantic processing of sentences engages more activity in the bilingual compared to the monolingual brain and, more specifically, in the inferior frontal gyrus. The present study aims to extend those results and examines whether semantic and also grammatical sentence processing involve different cerebral structures when testing in the native language. In this regard, highly proficient Spanish/Catalan bilinguals and Spanish monolinguals made grammatical and semantic judgments in Spanish while being scanned. Results showed that both types of judgments recruited more cerebral activity for bilinguals in language-related areas including the superior and middle temporal gyri. Such neural differences co-occurred with similar performance at the behavioral level. Taken together, these data suggest that early bilingualism shapes the brain and cognitive processes in sentence comprehension even in their native language; on the other hand, they indicate that brain over activation in bilinguals is not constrained to a specific area.

Do bilinguals show neural differences with monolinguals when processing their native language?

The present research used fMRI to measure brain activity in passive listening and picture-naming tasks with a group of early high proficient Spanish-Catalan bilinguals, in which Spanish was dominant, and a group of Spanish monolinguals. Both tasks were conducted in Spanish and the effect of cognateness was studied. The behavioural results showed slow naming responses in bilinguals. The fMRI results revealed that bilinguals and monolinguals differed only during the picture naming task. Unlike previous results, obtained mainly with L2, monolinguals displayed more activity in receptive language areas and less activity in the posterior cingulate cortex and right STG in the picture-naming task than bilinguals. As far as we know, this is the first study to investigate the neural basis of L1 processing in bilinguals and monolinguals by performing the task in the same language and in a monolingual context. The results indicate more efficient use of language networks in monolinguals because bilinguals utilised a more distributed network, which may imply subtle processing disadvantages.

Age related-changes in the neural basis of self-generation in verbal paired associate learning

Verbal information is better retained when it is self-generated rather than when it is received passively. The application of self-generation procedures has been found to improve memory in healthy elderly and in individuals with impaired cognition. Overall, the available studies support the notion that active participation in verbal encoding engages memory mechanisms that supplement those used during passive observation. Thus, the objective of this study was to investigate the age-related changes in the neural mechanisms involved in the encoding of paired-associates using a self-generation method that has been shown to improve memory performance across the lifespan. Subjects were 113 healthy right-handed adults (Edinburgh Handedness Inventory >50; 67 females) ages 18–76, native speakers of English with no history of neurological or psychiatric disorders. Subjects underwent fMRI at 3 T while performing didactic learning (“read”) or self-generation learning (“generate”) of 30 word pairs per condition. After fMRI, recognition memory for the second word in each pair was evaluated outside of the scanner. On the post-fMRI testing more “generate” words were correctly recognized than “read” words (p < 0.001) with older adults recognizing the “generated” words less accurately (p < 0.05). Independent component analysis of fMRI data identified task-related brain networks. Several components were positively correlated with the task reflecting multiple cognitive processes involved in self-generated encoding; other components correlated negatively with the task, including components of the default-mode network. Overall, memory performance on generated words decreased with age, but the benefit from self-generation remained consistently significant across ages. Independent component analysis of the neuroimaging data revealed an extensive set of components engaged in self-generation learning compared with didactic learning, and identified areas that were associated with age-related changes independent of performance.

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Verbal information is better retained when self-generated vs. received passively.

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Application of self-generation is associated with better retention across ages.

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Generated words were retained better than read words.

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Several components of network for word generation were identified.

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Age-associated changes within the network are discussed.

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.

Marginal neurofunctional changes in high-performing older adults in a verbal fluency task

The maintenance of a high level of performance in aging has often been associated with changes in cerebral activations patterns for various cognitive components. However, relatively few studies have investigated this phenomenon in light of lexical speech production abilities, which have not been systematically found to benefit from neurofunctional reorganization during verbal fluency tasks. In this study, functional magnetic resonance imaging was used to assess overt self-paced semantic and orthographic verbal fluency tasks performed by healthy younger and older adults within a mixed block/event-related fMRI design. Behavioral results indicated similarly high levels of performance between tasks and age groups, while whole brain analysis revealed significant task-related differences in patterns of brain activity, but no significant effect of age or task-by-age interaction across the speech conditions. Only local activity differences were found between age groups. These marginal neurofunctional changes in high-performing older adults are discussed in terms of task demands.

Increased neural activity during overt and continuous semantic verbal fluency in major depression: mainly a failure to deactivate

Major depression is associated with impairments in semantic verbal fluency (VF). However, the neural correlates underlying dysfunctional cognitive processing in depressed subjects during the production of semantic category members still remain unclear. In the current study, an overt and continuous semantic VF paradigm was used to examine these mechanisms in a representative sample of 33 patients diagnosed with a current episode of unipolar depression and 33 statistically matched healthy controls. Subjects articulated words in response to semantic category cues while brain activity was measured with functional magnetic resonance imaging (fMRI). Compared to controls, patients showed poorer task performance. On the neural level, a group by condition interaction analysis, corrected for task performance, revealed a reduced task-related deactivation in patients in the right parahippocampal gyrus, the right fusiform gyrus, and the right supplementary motor area. An additional and an increased task-related activation in patients were observed in the right precentral gyrus and the left cerebellum, respectively. These results indicate that a failure to suppress potentially interfering activity from inferior temporal regions involved in default-mode network functions and visual imagery, accompanied by an enhanced recruitment of areas implicated in speech initiation and higher-order language processes, may underlie dysfunctional cognitive processing during semantic VF in depression. The finding that patients with depression demonstrated both decreased performance and aberrant brain activation during the current semantic VF task demonstrates that this paradigm is a sensitive tool for assessing brain dysfunctions in clinical populations.

A genome-wide supported psychiatric risk variant in NCAN influences brain function and cognitive performance in healthy subjects

The A allele of the single nucleotide polymorphism (SNP) rs1064395 in the NCAN gene has recently been identified as a susceptibility factor for bipolar disorder and schizophrenia. NCAN encodes neurocan, a brain-specific chondroitin sulfate proteoglycan that is thought to influence neuronal adhesion and migration. Several lines of research suggest an impact of NCAN on neurocognitive functioning. In the present study, we investigated the effects of rs1064395 genotype on neural processing and cognitive performance in healthy subjects. Brain activity was measured with functional magnetic resonance imaging (fMRI) during an overt semantic verbal fluency task in 110 healthy subjects who were genotyped for the NCAN SNP rs1064395. Participants additionally underwent comprehensive neuropsychological testing. Whole brain analyses revealed that NCAN risk status, defined as AA or AG genotype, was associated with a lack of task-related deactivation in a large left lateral temporal cluster extending from the middle temporal gyrus to the temporal pole. Regarding neuropsychological measures, risk allele carriers demonstrated poorer immediate and delayed verbal memory performance when compared to subjects with GG genotype. Better verbal memory performance was significantly associated with greater deactivation of the left temporal cluster during the fMRI task in subjects with GG genotype. The current data demonstrate that common genetic variation in NCAN influences both neural processing and cognitive performance in healthy subjects. Our study provides new evidence for a specific genetic influence on human brain function.

Age-related changes in functional network connectivity associated with high levels of verbal fluency performance

The relative preservation of receptive language abilities in older adults has been associated with adaptive changes in cerebral activation patterns, which have been suggested to be task-load dependent. However, the effects of aging and task demands on the functional integration of neural networks contributing to speech production abilities remain largely unexplored. In the present functional neuroimaging study, data-driven spatial independent component analysis and hierarchical measures of integration were used to explore age-related changes in functional connectivity among cortical areas contributing to semantic, orthographic, and automated word fluency tasks in healthy young and older adults, as well as to assess the effect of age and task demands on the functional integration of a verbal fluency network. The results showed that the functional integration of speech production networks decreases with age, while at the same time this has a marginal effect on behavioral outcomes in high-performing older adults. Moreover, a significant task demand/age interaction was found in functional connectivity within the anterior and posterior subnetworks of the verbal fluency network. These results suggest that local changes in functional integration among cortical areas supporting lexical speech production are modulated by age and task demands.

Genetic variation in CACNA1C affects neural processing in major depression

Genetic studies found the A allele of the single nucleotide polymorphism rs1006737 in the CACNA1C gene, which encodes for the alpha 1C subunit of the voltage-dependent, L-type calcium ion channel Cav1.2, to be overrepresented in patients with major depressive disorder (MDD). Altered prefrontal brain functioning and impaired semantic verbal fluency (SVF) are robust findings in these patients. A recent functional magnetic resonance imaging (fMRI) study found the A allele to be associated with poorer performance and increased left inferior frontal gyrus (IFG) activation during SVF tasks in healthy subjects. In the present study, we investigated the effects of rs1006737 on neural processing during SVF in MDD. In response to semantic category cues, 40 patients with MDD and 40 matched controls overtly generated words while brain activity was measured with fMRI. As revealed by whole brain analyses, genotype significantly affected brain activity in patients. Compared to patients with GG genotype, patients with A allele demonstrated increased task-related activation in the left middle/inferior frontal gyrus and the bilateral cerebellum. Patients with A allele also showed enhanced functional coupling between left middle/inferior and right superior/middle frontal gyri. No differential effects of genotype on SVF performance or brain activation were found between diagnostic groups. The current data provide further evidence for an impact of rs1006737 on the left IFG and demonstrate that genetic variation in CACNA1C modulates neural responses in patients with MDD. The observed functional alterations in prefrontal and cerebellar areas might represent a mechanism by which rs1006737 influences susceptibility to MDD.

Correspondence of executive function related functional and anatomical alterations in aging brain

Neurocognitive aging studies have focused on age-related changes in neural activity or neural structure but few studies have focused on relationships between the two. The present study quantitatively reviewed 24 studies of age-related changes in fMRI activation across a broad spectrum of executive function tasks using activation likelihood estimation (ALE) and 22 separate studies of age-related changes in gray matter using voxel-based morphometry (VBM). Conjunction analyses between functional and structural alteration maps were constructed. Overlaps were only observed in the conjunction of dorsolateral prefrontal cortex (DLPFC) gray matter reduction and functional hyperactivation but not hypoactivation. It was not evident that the conjunctions between gray matter and activation were related to task performance. Theoretical implications of these results are discussed.