Tracing the bilingual advantage in cognitive control: The role of flexibility in temporal preparation and category switching

Combined effects of transcranial direct current stimulation and aerobic exercise on inhibitory control function in healthy young adults: An event-related potential study

Transcranial direct current stimulation (tDCS) and aerobic exercise (AE) have been demonstrated to enhance inhibitory control function in healthy individuals separately. However, the potential benefits of combining these two interventions have yet to be fully explored. In this study, we aimed to use multiple event-related potential (ERP) components (P200, N200, and N450) to investigate the combined effects of tDCS and AE on the improvement of inhibitory control ability in healthy young adults. We evaluated the influence of this combined intervention on cognitive tasks involving inhibitory control function and basic information processing by performing the Stroop Word Color task. Our results showed that compared to the application of tDCS or AE alone, the combined intervention of tDCS and AE had a greater effect on improving inhibitory control function in healthy young adults. The amplitude of P200, N200, and N450 ERP components also changed more significantly during the Stroop Word Color task. We concluded that the mechanism of tDCS combined with AE in improving inhibitory control ability may involve synergistic effects on brain structures at different levels, such as regulating interactions at the reticular activating system level and activating corresponding brain regions at the medial frontal lobe and frontal lobe levels.

Synergistic effects of aerobic exercise and transcranial direct current stimulation on executive function and biomarkers in healthy young adults

OBJECTIVE

This research explored the combined effects of transcranial direct current stimulation (tDCS) and aerobic exercise (AE) on executive function and specific serum biomarkers in healthy adults.

METHODS

Sixty healthy young adults were randomly assigned into tDCS+AE, tDCS only, or AE only groups. Interventions were carried out for 20 days. Executive functions were evaluated using tasks such as the 2,3-back task, the spatial working memory task, the Stroop test, T test, and hexagonal obstacle jump task. Serum biomarkers, including brain-derived neurotrophic factor (BDNF), malondialdehyde (MDA), superoxide dismutase (SOD), glutamate, glutathione peroxidase 4 (GPX4) and iron ion, were analyzed pre- and post-intervention.

RESULTS

The tDCS+AE group showed superior enhancements in executive function, evidenced by improved accuracy rates in 2,3-back tasks, better performance in the staircase task, and reduced reaction times in the incongruent reaction time of the Stroop task compared to other groups. Importantly, we found substantial changes in serum biomarkers: increased levels of BDNF and SOD, and decreased levels of MDA and glutamate in the tDCS+AE group. These changes were significantly different when compared with the tDCS and AE only groups. Notably, these alterations in serum biomarkers were correlated with improvements in executive function tasks, thus offering a potential physiological basis for the cognitive improvements witnessed.

CONCLUSION

The combined tDCS and AE intervention effectively improved executive function in healthy young adults, with the improvements linked to changes in key serum biomarkers. The results emphasize the potential of combined tDCS and AE interventions in engaging multiple physiological pathways to enhance executive function.

Reconfiguration of response-set in task switching: Event-related potential evidence

In task switching, an interaction between task and response is often observed, with response repetition (RR) benefits in task-repeat trials and RR costs in task-switch trials. The theoretical accounts of the RR effect remain controversial, and neuroscience evidence is scarce. The present study utilized the event-related potentials (ERPs) method to explore the neural mechanism underlying the RR effect by adopting a cued task-switching paradigm. The ERP results revealed the interaction between task and response in the P3b time window, with a response switch positivity under task-repetition conditions and an RR positivity under task-switching conditions. In addition, there were RR positivity in the N2 irrespective of task transition and in the late component (LC, 550-600 ms) that only under the task repetition condition. On the individual level, the RR benefit positively correlated with the RR positivity in the LC, while the RR costs negatively correlated with RR positivity in the N2/P3 component. These results suggest that both response reconfiguration and episodic-retrieval make contributions to the RR effects, which were also discussed in terms of predictive model for a domain-general inference and learning of perceptual categories.

The effects of bilingualism on cognition and behaviour in individuals with attention deficits: A scoping review

Background

Weaknesses in executive function have persistently been found to be associated with Attention Deficit Hyperactivity Disorder (ADHD), while bilinguals have been argued to show advantages in executive functions. While there has been some research into how bilingualism affects cognitive skills and behaviour in individuals with attention deficits, the question is still very much open. The aim of this systematic review is to gather, synthesise and evaluate existing evidence on how bilingual language experience and attention deficits affect executive function performance and ADHD-related symptoms in children and adults.

Methods

Following PRISMA guidelines, a comprehensive literature search in relevant databases (PsycInfo, PubMed, Scopus, ERIC, Web of Science, EMBASE, MEDLINE, LLBA) was performed using search strings related to attention difficulties/ADHD and bilingualism. All quantitative studies were included that presented original empirical data on the combined effects of bilingualism and attention levels, regardless of age group and methodology. The screening procedure revealed nine relevant studies.

Results

Across the nine identified studies, a total of 2071 participants were tested. Of these, seven studies involved children and two adults. The studies varied considerably with respect to their design and methodology, the targeted executive function skills or behavioural symptoms, as well as their measure of bilingualism and attention levels. Most studies assessed aspects of executive function performance such as interference control, response inhibition, working memory or cognitive flexibility. Three studies looked at the effects of bilingualism on ADHD-related symptoms or ADHD diagnosis. Across the studies, no systematic advantage or disadvantage of bilingualism on cognitive performance or behaviour in people with attention deficits was observed.

Conclusion

The limited number of identified studies provide no consistent evidence that bilingualism alleviates or intensifies attention difficulties in adults or children with ADHD. Based on the current state of research, individuals with ADHD and their families should not be concerned that learning additional languages has a negative impact on functioning or cognitive performance.

Systematic review registration

https://doi.org/10.17605/OSF.IO/PK768.

The effects of a single aerobic exercise session on mood and neural emotional reactivity in depressed and healthy young adults: A late positive potential study

Depression has been characterized by lowered mood and unfavorable changes in neural emotional reactivity (altered brain responses to emotional stimuli). Physical exercise is a well-established strategy to improve the mood of healthy and depressed individuals. Increasing evidence suggests that exercise might also improve emotional reactivity in healthy adults by increasing or decreasing brain responses to positive or negative stimuli, respectively. It is unknown, however, if exercise could also benefit emotional reactivity in depressed individuals. We investigated the effects of a single aerobic exercise session on mood and emotional reactivity in 24 depressed and 24 matched healthy young adults. Self-reported mood and neural reactivity to emotional pictures (indexed by the EEG late positive potential, LPP) were assessed before and after two experimental protocols: exercise (36 min of moderate-intensity exercise at 75% of maximal heart rate) and seated rest condition (36 min). In the healthy control group, exercise improved self-reported mood and neural emotional reactivity (increasing LPP to positive pictures). In the depressed group, exercise improved self-reported mood; however, it did not affect neural emotional reactivity. Additional analyses performed on both groups revealed that exercise-induced changes in emotional reactivity are associated with the severity of depressive symptoms: the effectiveness of exercise in improving emotional reactivity decreases with the severity of depressive symptoms. Overall, the study further strengthens the claim of a beneficial role of exercise on mood and emotional reactivity. It also suggests that a single aerobic exercise session might have a limited influence on neural emotional reactivity in depressed individuals.

Words Versus Pictures: Bilingual Performance on Verbal and Pictorial Measures of Executive Functions

PURPOSE

This study examined bilinguals' performance on functional executive function map tasks such as the Zoo Map from the Behavioural Assessment of the Dysexecutive Syndrome and the extent to which working memory, set-shifting, and inhibition measures predicted bilinguals' performance on these tasks. Additionally, we explored the utility of pictorial map tasks as a measure of complex executive function in bilinguals. We hypothesized that bilinguals would perform better on the pictorial map tasks due to the reduced language processing demand.

METHOD

The analyses included 131 bilingual young adults who completed a comprehensive language history questionnaire, an English proficiency test, a battery of working memory and executive function tasks, and verbal and pictorial map tasks.

RESULTS

Contrary to predictions, bilinguals' performance on the verbal maps did not differ significantly from that on the pictorial maps. Two multiple regression models significantly predicted performance on the verbal and pictorial maps, accounting for 7%-25% of the variance in the map scores. Working memory and interference control were the most prominent predictors within these models.

CONCLUSIONS

In our study, bilinguals' performance on the verbal maps did not differ significantly from that on the pictorial maps. Additionally, English proficiency did not correlate with the participants' verbal map scores. These results suggest that executive function map tasks (e.g., the Zoo Map) are a useful clinical tool for assessing executive function in bilinguals. The findings of this study are discussed in light of the current literature on executive functions in bilinguals.

Do Bilinguals Outperform Monolinguals in Switching Tasks? Contrary Evidence for Nonlinguistic and Linguistic Switching Tasks

The benefits of bilingualism in executive functions are highly debated. Even so, in switching tasks, these effects seem robust, although smaller than initially thought (Gunnerud et al., 2020; Ware et al., 2020). By handling two languages throughout their lifespan, bilinguals appear to train their executive functions and show benefits in nonlinguistic switching tasks compared to monolinguals. Nevertheless, because bilinguals need to control for the interference of another language, they may show a disadvantage when dealing with task-switching paradigms requiring language control, particularly when those are performed in their less dominant language. The present work explored this issue by studying bilingualism's effects on task switching within the visual and language domains. On the one hand, our results show that bilinguals were overall faster and presented reduced switch costs compared to monolinguals when performing perceptual geometric judgments with no time for task preparation. On the other hand, no bilingual advantage was found when a new sample of comparable bilinguals and monolinguals completed a within-language switching task. Our results provide clear evidence favoring the bilingual advantage, yet only when the task imposes greater executive demands and does not involve language control.

The source of attention modulations in bilingual language contexts

Bilinguals who switch from a monolingual context to a bilingual context enhance their domain-general attentional system. But what drives the adaptation process and translates into the observed increased efficiency of the attentional system? To uncover the origin of the plasticity in a bilingual's language experience, we investigated whether switching between other types of categories also modulated domain-general attentional processes. We compared performance of Catalan-Spanish bilinguals across three experiments in which participants performed the Attentional Network Test in a mixed context and in two single contexts that were created by interleaving words with flankers. The contexts were related to switching (or not) between languages (Experiment-1) or between low-level perceptual color categories (Experiment-2) or between linguistic categories (Experiment-3). Both switching between languages and linguistic categories revealed increased target-P3 amplitudes in mixed contexts compared to single contexts. These findings can inform the Inhibitory Control model regarding the locus and domain-generality of attentional adaptations.

Something About the Way You Speak: A Meta-analysis on Children's Linguistic-based Social Preferences

There is growing interest in the role of linguistic cues (accents, dialects, language) in driving children's social preferences. This meta-analysis integrated 131 effect sizes involving 2,680 infants and children from 2 days old to 11 years. Overall, children prefer native-accent, native-dialect, and native-language speakers over non-native counterparts (d = 0.57). Meta-regression highlighted that bilinguals (d = 0.93) do not exhibit less native-speaker preference compared to monolinguals (d = 0.62). Children displayed stronger preferences based on accent (d = 1.04) than dialect (d = 0.44) and language (d = 0.39). Children's cultural background, exposure to non-native speech, age, and preference measure were not significant moderators. The data are discussed in light of several theoretical explanations for when and why children show linguistic-based social preferences.

Empirical investigation of the relationship between bilingualism and social flexibility

Recently, a relationship between bilingualism and enhanced social flexibility has been suggested. However, research on the subject is scarce and what little exists is limited by several conceptual and methodological concerns. In the current study, we attempted to (a) replicate the findings from a study by Ikizer and Ramírez-Esparza (Bilingualism: Language and Cognition 21:957–969, 2018) by using the scales that the authors developed, and (b) test the concept of social flexibility experimentally with a switch-task using socially relevant stimuli. In the first part, participants (n = 194) filled out the scales developed by Ikizer and Ramírez-Esparza. We could not find that bilingualism leads to enhanced social flexibility. We did, however, find that higher level of education led to higher scores on the social flexibility scale. In the second part, a subsample (n = 74) from Part 1 completed a task where they were asked to identify the congruency between a face and a voice based on either gender or emotion, and to switch between these two tasks. The experimental task did not show an advantage for the bilingual participants. On the contrary, higher proficiency in a second language led to lower accuracy in the congruent emotion condition, while level of education led to higher accuracy in that same condition. We suggest that factors other than bilingualism, such as level of education and biculturalism, most likely drove the effect found both in the current study and originally by Ikizer and Ramírez-Esparza.

Meta-Analysis Reveals a Bilingual Advantage That Is Dependent on Task and Age

Debate continues on whether a bilingual advantage exists with respect to executive functioning. This report synthesized the results of 170 studies to test whether the bilingual advantage is dependent on the task used to assess executive functioning and the age of the participants. The results of the meta-analyses indicated that the bilingual advantage was both task- and age-specific. Bilinguals were significantly faster than monolinguals (Hedges' g values ranged from 0.23 to 0.34), and significantly more accurate than monolinguals (Hedges' g values ranged between 0.18 and 0.49) on four out of seven tasks. Also, an effect of age was found whereby the bilingual advantage was larger for studies comprising samples aged 50-years and over (Hedges' g = 0.49), compared to those undertaken with participants aged between 18 and 29 years (Hedges' g = 0.12). The extent to which the bilingual advantage might be due to publication bias was assessed using multiple methods. These were Egger's Test of Asymmetry, Duval and Tweedie's Trim and Fill, Classic Fail-Safe N, and PET-PEESE. Publication bias was only found when using Egger's Test of Asymmetry and PET-PEESE method, but not when using the other methods. This review indicates that if bilingualism does enhance executive functioning, the effects are modulated by task and age. This may arise because using multiple languages has a highly specific effect on executive functioning which is only observable in older, relative to younger, adults. The finding that publication bias was not uniformly detected across the different methods raises questions about the impact that unpublished (or undetected) studies have on meta-analyses of this literature.

Regular Open-Skill Exercise Generally Enhances Attentional Resources Related to Perceptual Processing in Young Males

This study aimed to examine whether the regular open-skill exercise led to a selective improvement or a general improvement on cognitive function in healthy young males. Besides, we also intend to expand previous studies by looking into the temporal dynamics of early information processes and cognitive processes through appraising the extensive temporal series of stimulus-locked ERP components. Sixty healthy young males were classified into two groups: those who regularly participated in the open-skill exercise for at least 2 years (n = 30), and those who exercised rarely. The participants conducted the Stroop task with event-related brain potential (ERP) recorded. The results indicated that compared with the rare exercise group, the open-skill exercise group led to a selective improvement for accuracy under the incongruent condition. And the open-skill exercise group also led to a selective improvement for response time under the incongruent condition. Moreover, the open-skill exercise group yielded larger P200 amplitudes under both the congruent and incongruent conditions compared with the rare exercise group. The findings suggest that the regular open-skill exercise may promote executive function by an increase in the allocation of attentional resources related to perceptual processing and greater interference control during cognitively demanding tasks in healthy young males.

Acute Moderate-Intensity Exercise Generally Enhances Attentional Resources Related to Perceptual Processing

The present study aimed to investigate whether acute moderate-intensity exercise led to a selective effect on executive function tasks or general effect on cognitive tasks that involve executive function and basic information processing in young adults. Besides, we also aimed to examine acute exercise's effect on multiple ERP components (e.g., P2, N2, P3b, and N450) to expand previous research. Seventy-two young adults were randomly assigned to the exercise or control groups. The Stroop task was administrated before and after treatments (exercise or reading), and the P2, N2, P3b, and N450 components of the Event-Related Potential (ERP) waveform were recorded and analyzed. Larger P2 amplitudes on both congruent and incongruent tasks were observed following acute exercise. Acute exercise did not influence accuracy or response time, and no effects on N2, P3b, and N450 components were found. These findings suggest that acute moderate-intensity exercise may have a generally beneficial effect on mobilization of attentional resources related to perceptual processing and exercise-related physiological arousal.

Does the Bilingual Advantage in Cognitive Control Exist and If So, What Are Its Modulating Factors? A Systematic Review

Recently, doubts were raised about the existence of the bilingual advantage in cognitive control. The aim of the present review was to investigate the bilingual advantage and its modulating factors. We searched the Medline, ScienceDirect, Scopus, and ERIC databases for all original data and reviewed studies on bilingualism and cognitive control, with a cut-off date of 31 October 2018, thereby following the guidelines of the preferred reporting items for systematic reviews and meta-analysis (PRISMA) protocol. The results of the 46 original studies show that indeed, the majority, 54.3%, reported beneficial effects of bilingualism on cognitive control tasks; however, 28.3% found mixed results and 17.4% found evidence against its existence. Methodological differences seem to explain these mixed results: Particularly, the varying selection of the bilingual participants, the use of nonstandardized tests, and the fact that individual differences were often neglected and that longitudinal designs were rare. Therefore, a serious risk for bias exists in both directions (i.e., in favor of and against the bilingual advantage). To conclude, we found some evidence for a bilingual advantage in cognitive control; however, if significant progress is to be made, better study designs, bigger data, and more longitudinal studies are needed.

Verbal and Nonverbal Anticipatory Mechanisms in Bilinguals

Empirical evidence collected so far has revealed that the bilingual advantage cannot be reduced to a single component of the executive functioning, and point to the need to understand the effects of bilingual experience on cognition as influencing a wider family of mental processes, including, but not limited to, cognitive control. The present study aims to explore a relatively underinvestigated domain of bilingual cognitive processes, namely anticipation, through a series of different paradigms tapping proactive and reactive mechanisms at different levels of cognitive complexity and linguistic components. The sample included 25 adult bilinguals ([Formula: see text] years) and 25 monolinguals ([Formula: see text] years) matched for age, gender, and non-verbal IQ. Participants were administered two experimental tasks: Attentional Network Task (ANT), and auditory picture-word identification task. Compared to monolinguals, bilinguals showed overall faster reaction times and reduced conflict effect on both the ANT and the picture-word identification task. In addition, associations between performances in the nonverbal and the verbal tasks support the role of the nonverbal monitoring component on verbal anticipation. Results are discussed in light of a dynamic interaction between proactive and reactive mechanisms of cognitive control.

Trait Cheerfulness Does Not Influence Switching Costs But Modulates Preparation and Repetition Effects in a Task-Switching Paradigm

Many studies have shown the beneficial effect of positive emotions on various cognitive processes, such as creativity and cognitive flexibility. Cheerfulness, understood as an affective predisposition to sense of humor, has been associated with positive emotions. So far, however, no studies have shown the relevance of this dimension in cognitive flexibility processes. The aim of this research was to analyze the relationship between cheerfulness and these processes. To this end, we carried out two studies using a task-switching paradigm. Study 1 aimed at analyzing whether high trait cheerfulness was related to better cognitive flexibility (as measured by reduced task-switching costs), whereas Study 2 aimed at replicating the pattern of data observed in Study 1. The total sample was composed of 139 participants (of which 86 were women) selected according to their high versus low scores in trait cheerfulness. In a random way, participants had to judge whether the face presented to them in each trial was that of a man or a woman (gender recognition task) or whether it expressed anger or happiness (expressed emotion recognition task). We expected participants with high versus low trait cheerfulness to show a lower task-switching cost (i.e., higher cognitive flexibility). Results did not confirm this hypothesis. However, in both studies, participants with high versus low trait cheerfulness showed a higher facilitation effect when the stimuli attributes were repeated and also when a cue was presented anticipating the demand to perform. We discuss the relevance of these results for a better understanding of cheerfulness.

Neurodynamics of executive control processes in bilinguals: evidence from ERP and source reconstruction analyses

The present study was designed to examine the impact of bilingualism on the neuronal activity in different executive control processes namely conflict monitoring, control implementation (i.e., interference suppression and conflict resolution) and overcoming of inhibition. Twenty-two highly proficient but non-balanced successive French-German bilingual adults and 22 monolingual adults performed a combined Stroop/Negative priming task while event-related potential (ERP) were recorded online. The data revealed that the ERP effects were reduced in bilinguals in comparison to monolinguals but only in the Stroop task and limited to the N400 and the sustained fronto-central negative-going potential time windows. This result suggests that bilingualism may impact the process of control implementation rather than the process of conflict monitoring (N200). Critically, our study revealed a differential time course of the involvement of the anterior cingulate cortex (ACC) and the prefrontal cortex (PFC) in conflict processing. While the ACC showed major activation in the early time windows (N200 and N400) but not in the latest time window (late sustained negative-going potential), the PFC became unilaterally active in the left hemisphere in the N400 and the late sustained negative-going potential time windows. Taken together, the present electroencephalography data lend support to a cascading neurophysiological model of executive control processes, in which ACC and PFC may play a determining role.