Enhancement of phonemic verbal fluency in multilingual young adults by transcranial random noise stimulation.

Several studies have analyzed the effects of transcranial direct current stimulation on verbal fluency tasks in non-clinical populations. Nevertheless, the reported effects on verbal fluency are inconsistent. In addition, the effect of other techniques such as transcranial random noise stimulation (tRNS) on verbal fluency enhancement has yet to be studied in healthy multilingual populations. This study aims to explore the effects of tRNS on verbal fluency in healthy multilingual individuals. Fifty healthy multilingual (Spanish, English and Basque) adults were randomly assigned to a tRNS or sham group. Electrodes were placed on the left dorsolateral prefrontal cortex and left inferior frontal gyrus. All participants performed phonemic and semantic verbal fluency tasks before, during (online assessment) and immediately after (offline assessment) stimulation in three different languages. The results showed significantly better performance by participants who received tRNS in the phonemic verbal fluency tasks in Spanish (in the online and offline assessment) and English (in the offline assessment). No differences between conditions were found in Basque nor semantic verbal fluency. These findings suggests that tRNS on the left prefrontal cortex could help improve phonemic, yet not semantic, fluency in healthy multilingual adults.

Neuropsychological deficits in patients with persistent COVID-19 symptoms: a systematic review and meta-analysis.

Long-term persistent symptoms of COVID-19 affect 30-80% of patients who have recovered from the disease and may continue for a long time after the disease has been overcome. The duration of these symptoms over time might have consequences that affect different aspects of health, such as cognitive abilities. The main objective of this systematic review and meta-analysis was to objectify the persistent COVID-19 cognitive deficits after acute phase of infection and to summarize the existing evidence. Additionally, we aimed to provide a comprehensive overview to further understand and address the consequences of this disease. Our protocol was registered in PROSPERO (CRD42021260286). Systematic research was conducted in the Web of Science, MEDLINE, PubMed, PsycINFO, Scopus, and Google Scholar databases from January 2020 to September 2021. Twenty-five studies were included, six of which were analyzed for the meta-analysis, and consisted of 175 patients who had recovered from COVID-19 and 275 healthy individuals. Analyses of cognitive performance of post-COVID-19 patients and healthy volunteers were compared using a random-effects model. The results showed an overall medium-high effect size (g = -.68, p = .02) with a 95% CI (-1.05 to -.31), with a significantly moderate level of heterogeneity among studies (Z = 3.58, p < .001; I2 = 63%). The results showed that individuals who had recovered from COVID-19 showed significant cognitive deficits compared to controls. Future studies should carefully assess the long-term progression of cognitive impairments in patients with persistent COVID-19 symptoms, as well as the effectiveness of rehabilitation interventions. Nevertheless, there is an urgent need to know the profile to speed up development of prevention plans as well as specific interventions. Since more information is being obtained and more studies are being conducted on the subject, the need to examine this symptomatology multidisciplinary to achieve greater scientific evidence of its incidence and prevalence has become increasingly clear.

Effects of transcranial electrical stimulation techniques on foreign vocabulary learning.

Although the use of transcranial electrical stimulation (tES) techniques on healthy population has been linked to facilitating language learning, studies on their effects on foreign language learning processes are scarce and results remain unclear. The objective of this study was to analyze whether tES enhances foreign language learning processes. Sixty-four healthy native Spanish-speaking participants were randomly assigned to four groups (transcranial direct current, transcranial random noise, tDCS-tRNS stimulation, or sham). They completed two intervention sessions with a two-week gap in between. During the first session the participants received stimulation (1.5 mA) while learning new English words and then performed recall and recognition tasks. Learning was assessed at follow-up, two weeks later. No differences in learning between groups were observed in the first session (F(1,61)= .86; p = .36). At follow-up, significantly higher learning accuracy was observed after tRNS compared to sham (p = .037). These results suggest that tRNS could be helpful in improving the processes involved in foreign language vocabulary learning.

Comparing transcranial direct current stimulation and transcranial random noise stimulation over left dorsolateral prefrontal cortex and left inferior frontal gyrus: Effects on divergent and convergent thinking.

The essential role of creativity has been highlighted in several human knowledge areas. Regarding the neural underpinnings of creativity, there is evidence about the role of left dorsolateral prefrontal cortex (DLPFC) and left inferior frontal gyrus (IFG) on divergent thinking (DT) and convergent thinking (CT). Transcranial stimulation studies suggest that the left DLPFC is associated with both DT and CT, whereas left IFG is more related to DT. However, none of the previous studies have targeted both hubs simultaneously and compared transcranial direct current stimulation (tDCS) and random noise stimulation (tRNS). Additionally, given the relationship between cognitive flexibility and creativity, we included it in order to check if the improvement in creativity may be mediated by cognitive flexibility. In this double-blind, between-subjects study, 66 healthy participants were randomly assigned to one of three groups (N = 22) that received a transcranial direct current stimulation (tDCS), transcranial random noise stimulation (tRNS), or sham for 20 min. The tDCS group received 1.5 mA with the anode over the left DLPFC and cathode over the left IFG. Locations in tRNS group were the same and they received 1.5 mA of high frequency tRNS (100-500 Hz). Divergent thinking was assessed before (baseline) and during stimulation with unusual uses (UU) and picture completion (PC) subtests from Torrance Creative thinking Test, whereas convergent thinking was evaluated with the remote association test (RAT). Stroop test was included to assess cognitive flexibility. ANCOVA results of performance under stimulation (controlling for baseline performance) showed that there were significant differences in PC (F = 3.35, p = 0.042, n p 2 = 0.10) but not in UU (F = 0.61, p = 0.546) and RAT (F = 2.65, p = 0.079) scores. Post-hoc analyses showed that tRNS group had significantly higher scores compared to sham (p = 0.004) in PC. More specifically, tRNS showed higher performance in fluency (p = 0.012) and originality (p = 0.021) dimensions of PC compared to sham. Regarding cognitive flexibility, we did not find any significant effect of any of the stimulation groups (F = 0.34, p = 0.711). Therefore, no further mediation analyses were performed. Finally, the group that received tDCS reported more adverse effects than sham group (F = 3.46, p = 0.035). Altogether, these results suggest that tRNS may have some advantages over tDCS in DT.

Effects of transcranial electrical stimulation techniques on second and foreign language learning enhancement in healthy adults: A systematic review and meta-analysis.

BACKGROUND: Transcranial electrical stimulation (tES) techniques have been used to enhance different cognitive domains such as language in healthy adults. While several reviews and meta-analysis have been conducted on the effects of tES on different language skills (picture naming, verbal fluency, word reading), there has been little research conducted to date on the effects of tES on the processes involved in foreign language learning. OBJECTIVE: A meta-analysis was performed to quantify the effects of tES on foreign language learning processes (non-words, artificial grammar, and foreign languages), focusing on accuracy, response times and 1-week follow-up effects, if reported by the studies. RESULTS: Eleven studies that had sham condition were reviewed. Nine of them were analyzed, including five using within-participant design, and four that employed between-participant design. The final analysis encompassed nine studies with 279 healthy participants. The analysis showed moderate enhancing effects of tES on overall language learning (g = 0.50, 95 % CI [0.29, 0.71], p = .0001). However, results were not significant on follow up data (g = 0.54, 95 % CI [-0.12, 1.20], p = .07), and on response times (g = 0.50, 95 % CI [-0.1, 1.18], p = .10). The effects were significantly moderated by years of education. CONCLUSIONS: The results suggest that tES seems to enhance the mechanisms involved in foreign language learning; however, more research is needed to understand the impact scope of these techniques on language learning processes.

Effectiveness of Cognitive Rehabilitation in Parkinson's Disease: A Systematic Review and Meta-Analysis.

Cognitive deficits influence the quality of life of Parkinson's disease (PD) patients. In order to reduce the impact of cognitive impairment in PD, cognitive rehabilitation programs have been developed. This study presents a systematic review and meta-analysis regarding the effectiveness of cognitive rehabilitation in non-demented PD patients. Twelve articles were selected according to PRISMA guidelines. The systematic review showed that attention, working memory, verbal memory, executive functions and processing speed were the most frequently improved domains. Meta-analysis results showed moderate effects on global cognitive status (g = 0.55) and working memory (g = 0.50); small significant effects on verbal memory (g = 0.41), overall cognitive functions (g = 0.39) and executive functions (g = 0.30); small non-significant effects on attention (g = 0.36), visual memory (g = 0.29), verbal fluency (g = 0.27) and processing speed (g = 0.24); and no effect on visuospatial and visuoconstructive abilities (g = 0.17). Depressive symptoms showed small effect (g = 0.24) and quality of life showed no effect (g = -0.07). A meta-regression was performed to examine moderating variables of overall cognitive function effects, although moderators did not explain the heterogeneity of the improvement after cognitive rehabilitation. The findings suggest that cognitive rehabilitation may be beneficial in improving cognition in non-demented PD patients, although further studies are needed to obtain more robust effects.

In search for common patterns in aphasia: The case of Spanish wh-dependencies.

BACKGROUND: Research on comprehension of wh-dependencies in Broca's aphasia has resulted in discrepant findings, suggesting that structurally different languages may involve different comprehension patterns. AIMS: In the present study, we investigated whether Spanish speakers with Broca's aphasia rely on a language-specific cue that might facilitate comprehension of object wh-dependencies - the preposition a. Since the preposition a in Spanish indicates animate objects, reliance on this cue would facilitate comprehension of more demanding object wh-dependencies, cancelling out processing differences between structures with subject and object extractions. METHODS: We studied comprehension of subject vs. object quién ("who") and qué ("which") direct and embedded questions, and relative clauses introduced by que in seven speakers with aphasia (SWA): six with Broca's and one with mixed aphasia. Control data were obtained from ten neurologically intact elderly Spanish speakers. RESULTS: Mann-Whitney test revealed that compared to healthy controls, SWA had preserved comprehension of both subject and object who direct questions, object which direct questions, and object relative clauses. However, they exhibited considerably worse comprehension of subject which direct questions, all embedded questions regardless of the extraction site (subject, object) or type of wh-word (who, which), and subject relative clauses. Individual comprehension profiles obtained in a modified t-test and revised standardized difference test, while containing some variability, largely support lack of subject-object asymmetry and objects-better patterns. Furthermore, in direct questions, comprehension of who questions was better than the comprehension of which questions, while the opposite was found in embedded questions. CONCLUSIONS: The lack of significant subject-object asymmetry in most conditions, together with better comprehension of object than subject extractions in direct questions, indicates that Spanish SWA rely on the preposition a in the comprehension of object wh-dependencies. However, this strategy fails in more complex conditions (embedded questions), because the processing costs outweigh the facilitating effects of this cue, unless additional cues to the object are present (object relatives). The present findings have implications for the accounts of wh-dependencies in Broca's aphasia involving Discourse-linking, the Intervener hypothesis, and the Competition model.