Executive functioning moderates the decline of retrieval fluency in time

Mechanisms of Verbal Fluency Impairment in Stroke: Insights From "Strategic Indices" Derived From a Study of 337 Patients

Verbal fluency provides a unique index of the functional architecture of control functions because it reflects the interactions between executive processes and lower-level language processes. However, an evaluation of the number of correct words alone does not enable one to determine precisely which processes are impaired. This study investigates post-stroke fluency impairments, focusing on previously unexplored indices and their neuroanatomical correlates using voxel-based lesion symptom mapping (VLSM). In total, 337 patients and 851 controls performed letter and semantic fluency tests. Analyses included overall performance (correct responses) and strategic indices (errors, time course, frequency, switches, and cluster size). Stroke patients produced fewer correct responses, more rule-breaking errors, fewer words after 15″, fewer infrequent words, fewer switches, and smaller clusters in letter fluency. Switching was strongly associated with letter fluency, while clustering was more related to semantic fluency. VLSM identified left-hemisphere structures, particularly frontal tracts (e.g., anterior thalamic and frontostriatal tracts), associated with switching, and a smaller set of left-hemisphere structures linked to clustering. Conceptually, the findings suggest stroke-related fluency disorders primarily arise from impairments in executive strategic search, as indicated by switching impairments, with weaker impairment on lexicosemantic abilities. The rarity of rule-breaking and perseverative errors indicates that inhibition and working memory deficits do not significantly contribute to poor fluency. The patients' production of infrequent words and fluency worsened over time, although the precise contributions of the three core processes to these additional changes require further investigation. Our results highlight the importance of detailed fluency evaluations in stroke patients for optimized rehabilitation.

Investigating the cognitive architecture of verbal fluency: evidence from an interference design on 487 controls

Introduction

Numerous studies have explored the linguistic and executive processes underlying verbal fluency using association designs, which provide limited evidence. To assess the validity of our model, we aimed to refine the cognitive architecture of verbal fluency using an interference design.

Methods

A total of 487 healthy participants performed letter and semantic fluency tests under the single condition and dual conditions while concurrently performing a secondary task that interferes with speed, semantics, phonology, or flexibility. We examined the effect of such interference on fluency indices including correct responses, clustering, switching, and time course.

Results

(1) All secondary tasks decreased fluency (p < 0.0001, all), (2) including a simple concurrent task that solely engages the attentional activation system (i.e., speed interference) and (3) a complex concurrent task that affects the ability to alternate (i.e., flexibility interference). (4) Linguistic secondary tasks (which engage phonological and semantic processes, in addition to attention) led to a greater decrease in fluency than speed interference (p < 0.0001), (5) with a more pronounced decrease in semantic fluency induced by semantic interference (p < 0.0001), and (6) the highest decrease in all types of fluency induced by phonological interference (p < 0.0001). In terms of derived indices, (7) speed interference decreased switching without affecting clustering (p < 0.0001) and (8) phonological interference mainly affected the first time interval, whereas speed and flexibility interference primarily affected the last time interval (p < 0.0001, all).

Discussion

These results, based on an interference design, indicate that letter and semantic fluency involve output lexico-phonological and semantic processes with which the strategic search process interacts, as well as an attentional component necessary to accelerate overall processing. These results also highlight interactions with other executive processes, such as those involved in stimulus dimension alternation, which require further analysis. They support our model and provide information concerning derived indices. The commonly claimed associations of executive function with switching and of semantic ability with clustering are only partially supported by our results. Finally, word production appears to be modulated by different cognitive processes over time, with a prominence of the phonological output lexicon in early production and more demanding processing (i.e., executive functioning) in late production.

Breathing signatures of semantic and phonemic verbal fluency and their impact on test performance in a sample of young Norwegian adults

Verbal fluency (VF) represents an important aspect of intelligence, in which oral word generation is demanded following semantic or phonemic cues. Two reliable phenomena of VF execution have been reported: A decay in performance across 1-minute trial and a discrepancy score between the semantic and phonemic VF tests (VFTs). Although, these characteristics have been explained from various cognitive standpoints, the fundamental role of speech breathing has not yet been considered. Therefore, the present study aims to evaluate the role of respiratory function for word generation in VFTs in healthy individuals. Thirty healthy young adults performed VFTs during definite periods of 1 minute while wearing a pneumotachograph mask. Duration, peak and volume of airflow were acquired during inspirations and expirations. Also, respiratory rate and acoustic data of verbal responses were registered, and accuracy scores were calculated. Each 1-minute trial was divided into four intervals of 15-seconds where parameters were calculated. Repeated measures ANOVAs and repeated measures correlations were used in the statistical analyses. Data revealed that respiratory function was significantly coupled to VF performance mostly during inhalations. Small but constant increments of inhale airflow occurred in phonemic VFT as well as higher peak airflow in both tasks, being higher for semantic VFT. High respiratory rate characterized performance of both VFTs across intervals. Airflow adjustments corresponded to better VF accuracy, while increments in respiratory rate did not. The present study shows a complex interplay of breathing needs during VF performance that varies along the performance period and that notably connects to inspirations.

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.

Assessment of Automatic and Controlled Retrieval Using Verbal Fluency Tasks

Category and letter verbal fluency assessment is widely used in basic and clinical research. Yet, the nature of the processes measured by such means remains a matter of debate. To delineate automatic (free-associative) versus controlled (dissociative) retrieval processes involved in verbal fluency tasks, we carried out a psychometric study combining a novel lexical-semantic retrieval paradigm and structural equation modeling. We show that category fluency primarily engages a free-associative retrieval, whereas letter fluency exerts executive suppression of habitual semantic associates. Importantly, the models demonstrated that this dissociation is parametric rather than absolute, exhibiting a degree of unity as well as diversity among the retrieval measures. These findings and further exploratory analyses validate that category and letter fluency tasks reflect partially distinct forms of memory search and retrieval control, warranting different application in basic research and clinical assessment. Finally, we conclude that the novel associative-dissociative paradigm provides straightforward and useful behavioral measures for the assessment and differentiation of automatic versus controlled retrieval ability.

Neuroendocrine response to a psychosocial stress test is not related to schizotypy but cortisol elevation predicts inflexibility of semantic memory retrieval

An altered stress response can contribute to the transition from preclinical psychotic symptoms to the clinical manifestation of schizophrenia and other psychotic disorders. The present study was aimed at testing the hypotheses that (i) the autonomic and neuroendocrine responses under psychosocial stress are dysregulated in individuals with high psychosis proneness (schizotypy); (ii) the magnitude of post-stress autonomic activation and cortisol release predicts alterations in semantic memory retrieval. The study was performed in 73 healthy individuals of both sexes with either high or low schizotypal traits preselected out of 609 individuals using the Schizotypal Personality Questionnaire. A psychosocial stress procedure based on public speech was used as a stress model. We found that individuals with high schizotypy engaged in less adaptive emotional stress-coping strategies than low schizotypy individuals. Yet, the neuroendocrine, immune, and sympathetic activation in response to the stress test was not different between the groups. Irrespective of the exposure to the stressor, individuals with high schizotypy were less fluent when retrieving associations from semantic memory. In addition, we demonstrated that acute psychosocial stress reduced the flexibility of semantic memory retrieval. The post-stress mental inflexibility was reliably predicted by the concomitant elevation of cortisol concentrations in saliva. The present study thus brings novel evidence indicating that the acute psychosocial challenge impairs retrieval flexibility in the semantic domain, which may be due to neuroendocrine activation.

Response modularity moderates how executive control aids fluent semantic memory retrieval

ABSTRACTEmerging work in semantic cognition has begun to elucidate the interaction between the structure of semantic memory and processes mediating goal-directed memory retrieval. Despite having essential implications for basic and applied research, these objectives remain neglected in both the assessment and interpretation of semantic verbal fluency (SVF) tasks. To test the association between semantic structure and the controlled processes underlying verbal fluency, we assessed how the degree of partitioning (modularity) of SVF responses into semantic clusters moderates the relationship of retrieval fluency with working memory and interference control capacities. We found that working memory capacity predicted retrieval fluency in individuals whose SVF responses were arranged in fine-grained semantic clusters (high modularity), whereas interference control was more predictive of retrieval fluency for individuals who delivered responses of low modularity. Our data support the presumed role of working memory and interference control in SVF and provide novel evidence that relative demands on these capacities are predicted by the organisation of semantic knowledge.

Differential effects of executive load on automatic versus controlled semantic memory retrieval

Growing evidence indicates that a domain-general executive control supports semantic memory retrieval, yet the nature of this interaction remains elusive. To shed light on such control mechanisms, we conducted two dual-task experiments loading distinct executive capacities (working memory maintenance, monitoring, and switching), while participants carried out automatic (free-associative) and controlled (dissociative) word retrieval tasks. We found that these forms of executive load interfered with retrieval fluency in both tasks, but these negative effects were more pronounced for the dissociative performance. Together, these findings indicate that the domain-general executive control supports accessing contextually relevant knowledge as well as the inhibition of automatically activated but task-inappropriate retrieval candidates, putatively via an adaptive gating of semantic activation and interference control. Moreover, the processing costs related to retrieval inhibition and switching were negatively correlated, suggesting a trade-off between the ability to constrain semantic activation (i.e., inhibition) and the ability to initiate flexible transitions between semantic sets (i.e., switching), which may thus represent two complementary control functions governing semantic memory retrieval.