Combined and Isolated Effects of Acute Exercise and Brain Stimulation on Executive Function in Healthy Young Adults

Evaluating the efficacy of cranial electrotherapy stimulation in mitigating anxiety-induced cognitive deficits

Cranial electrotherapy stimulation (CES) is a form of non-invasive brain stimulation (NIBS) that has demonstrated potential to modulate neural activity in a manner that may be conducive to improved cognitive performance. While other forms of NIBS, such as transcranial direct current stimulation (tDCS), have received attention in the field as potential acute cognitive enhancers, CES remains relatively unexplored. The current study aimed to assess the efficacy of CES in improving acute cognitive performance under normal experimental conditions, as well as during sessions of induced situational anxiety (threat of shock or ToS). To study this question, participants completed a cognitive battery assessing processing speed and distinct aspects of executive functioning (working memory, inhibition, and task switching) in two separate sessions in which they received active and sham CES. Participants were randomly assigned to between subject groups of either situational anxiety (ToS) or control condition (no ToS). We predicted that active CES would improve performance on assessments of executive functioning (working memory, inhibition, and task switching) relative to sham CES under ToS. We did not find any significant effects of ToS, CES, or an interaction between ToS and CES for any measures of executive functioning or processing speed. These findings suggest that a single dose of CES does not enhance executive functioning or processing speed under normal conditions or during ToS.

Effects of high-intensity interval training combined with dual-site transcranial direct current stimulation on inhibitory control and working memory in healthy adults

Transcranial direct current stimulation (tDCS) and high-intensity interval training (HIIT) have been demonstrated to enhance inhibitory control and working memory (WM) performance in healthy adults. However, the potential benefits of combining these two interventions have been rarely explored and remain largely speculative. This study aimed to explore the effects of acute HIIT combined with dual-site tDCS over the dorsolateral prefrontal cortex (DLPFC, F3 and F4) on inhibitory control and WM in healthy young adults. Twenty-five healthy college students (20.5 ± 1.3 years; 11 females) were recruited to complete HIIT + tDCS, HIIT + sham-tDCS, rest + tDCS, and rest + sham-tDCS (CON) sessions in a randomized crossover design. tDCS or sham-tDCS was conducted after completing HIIT or a rest condition of the same duration. The Stroop and 2-back tasks were used to evaluate the influence of this combined intervention on cognitive tasks involving inhibitory control and WM performance in post-trials, respectively. Response times (RTs) of the Stroop task significantly improved in the HIIT + tDCS session compared to the CON session across all conditions (all p values <0.05), in the HIIT + tDCS session compared to the rest + tDCS session in the congruent and neutral conditions (all p values <0.05), in the HIIT + sham-tDCS session compared to the CON session in the congruent and neutral conditions (all p values <0.05), in the HIIT + sham-tDCS session compared to the rest + tDCS session in the congruent condition (p = 0.015). No differences were found between sessions in composite score of RT and accuracy in the Stroop task (all p values >0.05) and in the 2-back task reaction time and accuracy (all p values >0.05). We conclude that acute HIIT combined with tDCS effectively improved inhibitory control but it failed to yield cumulative benefits on inhibitory control and WM in healthy adults. These preliminary findings help to identify beneficial effects of combined interventions on cognitive performance and might guide future research with clinical populations.

Towards optimized methodological parameters for maximizing the behavioral effects of transcranial direct current stimulation

Introduction

Transcranial direct current stimulation (tDCS) administers low-intensity direct current electrical stimulation to brain regions via electrodes arranged on the surface of the scalp. The core promise of tDCS is its ability to modulate brain activity and affect performance on diverse cognitive functions (affording causal inferences regarding regional brain activity and behavior), but the optimal methodological parameters for maximizing behavioral effects remain to be elucidated. Here we sought to examine the effects of 10 stimulation and experimental design factors across a series of five cognitive domains: motor performance, visual search, working memory, vigilance, and response inhibition. The objective was to identify a set of optimal parameter settings that consistently and reliably maximized the behavioral effects of tDCS within each cognitive domain.

Methods

We surveyed tDCS effects on these various cognitive functions in healthy young adults, ultimately resulting in 721 effects across 106 published reports. Hierarchical Bayesian meta-regression models were fit to characterize how (and to what extent) these design parameters differentially predict the likelihood of positive/negative behavioral outcomes.

Results

Consistent with many previous meta-analyses of tDCS effects, extensive variability was observed across tasks and measured outcomes. Consequently, most design parameters did not confer consistent advantages or disadvantages to behavioral effects-a domain-general model suggested an advantage to using within-subjects designs (versus between-subjects) and the tendency for cathodal stimulation (relative to anodal stimulation) to produce reduced behavioral effects, but these associations were scarcely-evident in domain-specific models.

Discussion

These findings highlight the urgent need for tDCS studies to more systematically probe the effects of these parameters on behavior to fulfill the promise of identifying causal links between brain function and cognition.

Aerobic fitness as a moderator of acute aerobic exercise effects on executive function

This study aimed to investigate the moderating role of aerobic fitness on the effect of acute exercise on improving executive function from both behavioral and cerebral aspects. Thirty-four young individuals with motor skills were divided into high- and low-fitness groups based on their maximal oxygen uptake. Both groups completed 30 min of moderate-intensity aerobic exercise on a power bike. Executive function tests (Flanker, N-back, More-odd-shifting) were performed before and after exercise and functional near-infrared spectroscopy was used to monitor prefrontal cerebral blood flow changes during the tasks. The results indicated significant differences between the two groups regarding executive function. Participants with lower aerobic fitness performed better than their higher fitness counterparts in inhibitory control and working memory, but not in cognitive flexibility. This finding suggests that the aerobic fitness may moderate the extent of cognitive benefits gained from acute aerobic exercise. Furthermore, the neuroimaging data indicated negative activation in the frontopolar area and dorsolateral prefrontal cortex in response to three complex tasks. These findings underscore the importance of considering individual aerobic fitness when assessing the cognitive benefits of exercise and could have significant implications for tailoring fitness programs to enhance cognitive performance.

Balancing Act: Acute and Contextual Vestibular Sensations of Cranial Electrotherapy Stimulation Using Survey and Sensor Outcomes in a Non-Clinical Sample

Cranial electrotherapy stimulation (CES) delivers low-intensity electrical currents to the brain to treat anxiety, depression, and pain. Though CES is considered safe and cost-effective, little is known about side effects emerging across different contexts. Our objective was to investigate how varying physical and cognitive demands impact the frequency and intensity of CES vestibular sensations in a sample of healthy young adults. We used a 2 (stimulation: sham, active) × 2 (physical demand: static sway, dynamic sit-to-stand) × 2 (cognitive demand: single-task remain silent, dual-task count backward) repeated measures design. Vestibular sensations were measured with surveys and wearable sensors capturing balance changes. Active stimulation did not influence reported vestibular sensations. Instead, high physical demand predicted more sensation reports. High cognitive demand, but not active stimulation, predicted postural sway unsteadiness. Significant effects of active stimulation on balance were observed only during the dynamic sit-to-stand transitions. In summary, CES induces vestibular sensations only for a specific outcome under certain circumstances. Our findings imply that consumers can safely maximize the benefits of CES while ensuring they are taking steps to minimize any potential side effects by considering their context and circumstances.

The Immediate and Sustained Effects of Moderate-Intensity Continuous Exercise and High-Intensity Interval Exercise on Working Memory

This study investigated the immediate and delayed effects of moderate-intensity continuous exercise (MICE) and high-intensity interval exercise (HIIE) on working memory. Fifty healthy young adults (mean age = 19.96 ± 1.03 years) engaged in (1) a MICE session, 20 min of continuous running on a treadmill at an intensity of 40–59% of heart rate reserve (HRR); (2) a HIIE session, 10 sets of 1 min running at an intensity of 90% HRR, interspersed by 1 min self-paced walking at 50% HRR; and (3) a control session, resting in a chair and reading books for 24 min. A spatial 2-back task was performed to assess working memory before, immediately after and 30 min after each intervention. Reaction time in the 2-back task was significantly reduced immediately after both MICE and HIIE interventions. The enhanced working memory associated with HIIE sustained for 30 min after the exercise, whereas the beneficial effects associated with MICE returned to the pre-exercise level at 30 min after the exercise. These results suggest that although both MICE and HIIE enhance working memory in young adults, the positive effect sustains longer in HIIE than that in MICE. The current study extends the existing knowledge base by suggesting that improvements in working memory with HIIE last longer than with MICE.

Modulating Cognitive–Motor Multitasking with Commercial-off-the-Shelf Non-Invasive Brain Stimulation

One growing area of multitasking research involves a focus on performing cognitive and motor tasks in tandem. In these situations, increasing either cognitive or motor demands has implications for performance in both tasks, an effect which is thought to be due to competing neural resources. Separate research suggests that non-invasive brain stimulation may offer a means to mitigate performance decrements experienced during multitasking. In the present study, we investigated the degree to which a commercially available non-invasive brain stimulation device (Halo Sport) alters balance performance in the presence of different types of cognitive demands. Specifically, we tested if performing a secondary cognitive task impacts postural sway in healthy young adults and if we could mitigate this impact using transcranial direct current stimulation (tDCS) applied over the primary motor cortex. Furthermore, we included conditions of unstable and stable surfaces and found that lower surface stability increased postural sway. In addition, we found that cognitive load impacted postural sway but in the opposite pattern we had anticipated, with higher sway found in the single-task control condition compared to executive function conditions. Finally, we found a small but significant effect of tDCS on balance with decreased sway for active (compared to sham) tDCS.

Four-week Tai Chi intervention decreases attention bias to drug cues in individuals with methamphetamine use disorder

Background: Mind-body exercise is used for the rehabilitation of individuals with methamphetamine use disorder (MUD). Attention bias to substances is an important index of MUD. However, whether a mind-body exercise intervention can decrease attention bias is unclear.Objective: This study aimed to test the effect of a four-week Tai Chi (a Chinese traditional mind-body exercise) exercise program on the attention bias of individuals with MUD.Methods: Thirty-two men with MUD and without Tai Chi practice experience were recruited and randomly assigned to either a Tai Chi exercise group or a control group. The Tai Chi group received four-week Tai Chi training, while the control group engaged in daily exercise (including radio gymnastics and Jianxincao, two kinds of free-hand exercises). During a drug-related Stroop task, participants were instructed to respond to the color of the word ignoring the word type (drug-related or neutral words). The reaction time and d' (the index of sensitivity) were measured.Results: The participants showed attention bias to substance cues; the reaction time was slower for drug-related words than for neutral words (p < .05). After the Tai Chi intervention, the Tai Chi group showed a faster reaction time (ps < .05) and a smaller d' (ps < .05) than the baseline across all the word types. In contrast, the control group showed no differences (ps > .05).Conclusion: Four-week Tai Chi intervention reduced sensitivity and attentional bias to drug-related cues in individuals with MUD, suggesting that mind-body exercise might enhance recovery from MUD via attention control.

Identifying regions in prefrontal cortex related to working memory improvement: A novel meta-analytic method using electric field modeling

Altering cortical activity using transcranial direct current stimulation (tDCS) has been shown to improve working memory (WM) performance. Due to large inter-experimental variability in the tDCS montage configuration and strength of induced electric fields, results have been mixed. Here, we present a novel meta-analytic method relating behavioral effect sizes to electric field strength to identify brain regions underlying largest tDCS-induced WM improvement. Simulations on 69 studies targeting left prefrontal cortex showed that tDCS electric field strength in lower dorsolateral prefrontal cortex (Brodmann area 45/47) relates most strongly to improved WM performance. This region explained 7.8 % of variance, equaling a medium effect. A similar region was identified when correlating WM performance and electric field strength of right prefrontal tDCS studies (n = 18). Maximum electric field strength of five previously used tDCS configurations were outside of this location. We thus propose a new tDCS montage which maximizes the tDCS electric field strength in that brain region. Our findings can benefit future tDCS studies that aim to affect WM function.

Prefrontal high definition cathodal tDCS modulates executive functions only when coupled with moderate aerobic exercise in healthy persons

Transcranial direct current stimulation (tDCS) is a promising tool to enhance cognitive performance. However, its effectiveness has not yet been unequivocally shown. Thus, here we tested whether coupling tDCS with a bout of aerobic exercise (AE) is more effective in modulating cognitive functions than tDCS or AE alone. One hundred twenty-two healthy participants were assigned to five randomized controlled crossover experiments. Two multimodal target experiments (EXP-4: anodal vs. sham tDCS during AE; EXP-5: cathodal vs. sham tDCS during AE) investigated whether anodal (a-tDCS) or cathodal tDCS (c-tDCS) applied during AE over the left dorsolateral prefrontal cortex (left DLPFC) affects executive functioning (inhibition ability). In three unimodal control experiments, the participants were either stimulated (EXP-1: anodal vs. sham tDCS, EXP-2: cathodal vs. sham tDCS) or did AE (EXP-3: AE vs. active control). Participants performed an Eriksen flanker task during ergometer cycling at moderate intensity (in EXP. 3-5). Only c-tDCS during AE had a significant adverse effect on the inhibition task, with decreased accuracy. This outcome provides preliminary evidence that c-tDCS during AE over the left DLPFC might effectively modulate inhibition performance compared to c-tDCS alone. However, more systematic research is needed in the future.