Transcranial direct current stimulation influences the cardiac autonomic nervous control

Does a single session of transcranial direct current stimulation enhance both physical and psychological performance in national- or international-level athletes? A systematic review

Some studies showed that a single session of transcranial direct current stimulation (tDCS) has the potential of modulating motor performance in healthy and athletes. To our knowledge, previously published systematic reviews have neither comprehensively investigated the effects of tDCS on athletic performance in both physical and psychological parameters nor investigated the effects of tDCS on high-level athletes. We examined all available research testing a single session of tDCS on strength, endurance, sport-specific performance, emotional states and cognitive performance for better application in competition and pre-competition trainings of national- or international-level athletes. A systematic search was conducted in PubMed, Web of Science, EBSCO, Embase, and Scopus up until to June 2023. Studies were eligible when participants had sports experience at a minimum of state and national level competitions, underwent a single session of tDCS without additional interventions, and received either sham tDCS or no interventions in the control groups. A total of 20 experimental studies (224 participants) were included from 18 articles. The results showed that a single tDCS session improved both physical and psychological parameters in 12 out of the 18 studies. Of these, six refer to the application of tDCS on the motor system (motor cortex, premotor cortex, cerebellum), five on dorsolateral prefrontal cortex and two on temporal cortex. The most sensitive to tDCS are strength, endurance, and emotional states, improved in 67%, 75%, and 75% of studies, respectively. Less than half of the studies showed improvement in sport-specific tasks (40%) and cognitive performance (33%). We suggest that tDCS is an effective tool that can be applied to competition and pre-competition training to improve athletic performance in national- or international-level athletes. Further research would explore various parameters (type of sports, brain regions, stimulation protocol, athlete level, and test tasks) and neural mechanistic studies in improving efficacy of tDCS interventions. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022326989, identifier CRD42022326989.

A pilot randomized controlled trial of transcranial direct current stimulation adjunct to moderate-intensity aerobic exercise in hypertensive individuals

Background

Hypertension is a global issue that is projected to worsen with increasingly obese populations. The central nervous system including the parts of the cortex plays a key role in hemodynamic stability and homeostatic control of blood pressure (BP), making them critical components in understanding and investigating the neural control of BP. This study investigated the effects of anodal transcranial direct current stimulation (tDCS) associated with aerobic physical exercise on BP and heart rate variability in hypertensive patients.

Methods

Twenty hypertensive patients were randomized into two groups: active tDCS associated with aerobic exercise or sham tDCS associated with aerobic exercise. BP and heart rate variability were analyzed before (baseline) and after twelve non-consecutive sessions. After each tDCS session (2 mA for 20 min), moderate-intensity aerobic exercise was carried out on a treadmill for 40 min.

Results

A total of 20 patients were enrolled (53.9 ± 10.6 years, 30.1 ± 3.7 Kg/m2). There were no significant interactions between time and groups on diastolic BP during wake, sleep, over 24 and 3 h after the last intervention. Heart rate variability variables showed no significant difference for time, groups and interaction analysis, except for HF (ms2) between groups (p < 0.05).

Conclusion

Anodal tDCS over the temporal cortex associated with aerobic exercise did not induce improvements in BP and heart rate variability.

Clinical trial registration

https://ensaiosclinicos.gov.br/rg/RBR-56jg3n/1, identifier: RBR-56jg3n.

Anodal transcranial direct current stimulation associated with aerobic exercise on the functional and physical capacity of patients with heart failure with reduced ejection fraction: ELETRIC study protocol

BACKGROUND

The hallmark symptom of heart failure (HF) is severe exercise intolerance. Fortunately, accumulated evidence suggests that exercise programs improve physical performance, enhance autonomy in daily activities and quality of life, and reduce cardiovascular and other hospitalizations. Recently, experimental studies have explored the application of non-invasive brain stimulation techniques, especially transcranial direct current stimulation (tDCS), aiming to improve physical performance due to its ability to modulate brain functioning. The primary objective of the present study is to evaluate the effects of anodal tDCS associated with aerobic exercise on the functional capacity of patients with HF with reduced ejection fraction (HFrEF). Secondary objectives are to compare the effects of tDCS associated with aerobic exercise vs. sham-tDCS associated with aerobic exercise on cardiopulmonary exercise capacity; inflammatory cytokines; and quality of life.

METHODS

This is a two-arm, prospectively registered, randomized trial with concealed allocation, double-blind, and intention-to-treat analysis. Forty-four patients with HFrEF will be recruited. The experimental group will undertake 25-30 min aerobic exercise training associated with tDCS, for 4 weeks. The control group will undergo the same aerobic exercise training, but with sham-tDCS. The primary outcome will be functional performance by the 6-min walk test. Secondary outcomes will include cardiopulmonary exercise capacity, inflammatory cytokines, and quality of life. Outcomes will be collected by a researcher blinded to group allocation at baseline (T0) and after 4 weeks of intervention (T1).

DISCUSSION

Although previous studies have investigated the combined effect of tDCS on T3 area and physical performance and have suggested that tDCS could have reduced ratings of perceived exertion by affecting the activity of the insular cortex, and therefore increase exercise tolerance, this study is the first to evaluate the effects of the addition of anodal tDCS to aerobic exercise training for improving physical and functional performance, decreasing the perceived exertion, altering the quantification of inflammatory cytokines, and improving the subclinical values of the cardiopulmonary test in patients with HFrEF, which could result in an important advance in cardiac rehabilitation for patients with chronic HF.

TRIAL REGISTRATION

Brazilian Registry of Clinical Trials (ReBEC) RBR-10w787j6. Registered on 25 April 2023. https://ensaiosclinicos.gov.br/pesquisador.

No effect of prefrontal transcranial direct current stimulation (tDCS) on food craving, food reward and subjective appetite in females displaying mild-to-moderate binge-type behaviour

Previous work suggests there may be an effect of transcranial direct current stimulation (tDCS) on appetite control in people at risk of overconsumption, however findings are inconsistent. This study aimed to further understand the potential eating behaviour trait-dependent effect of tDCS, specifically in those with binge-type behaviour. Seventeen females (23 ± 7 years, 25.4 ± 3.8 kg m-2) with mild-to-moderate binge eating behaviour completed two sessions of double-blind, randomised and counterbalanced anodal and sham tDCS applied over the right dorsolateral prefrontal cortex at 2.0 mA for 20 min. Subjective appetite visual analogue scales (VAS), the Food Craving Questionnaire-State (FCQ-S), and Leeds Food Preference Questionnaire (LFPQ) were completed pre- and post-tDCS. Participants then consumed a fixed-energy meal, followed by the VAS, FCQ-S and LFPQ. No difference between pre- and post-tDCS scores were found across fullness (p = 0.275, BF10 = 0.040), prospective consumption (p = 0.127, BF10 = 0.063), desire to eat (p = 0.247, BF10 = 0.054) or FCQ-S measures (p = 0.918, BF10 = 0.040) when comparing active and sham protocols. Only explicit liking and wanting for high-fat sweet foods were significantly different between conditions, with increased scores following active tDCS. When controlling for baseline hunger, the significant differences were removed (p = 0.138 to 0.161, BF10 = 0.810 to 1.074). The present data does not support the eating behaviour trait dependency of tDCS in a specific cohort of female participants with mild-to-moderate binge eating scores, and results align with those from individuals with healthy trait scores. This suggests participants with sub-clinical binge eating behaviour do not respond to tDCS. Future work should further explore effects in clinical and sub-clinical populations displaying susceptibility to overconsumption and weight gain.

Preemptive transcranial direct current stimulation induces analgesia, prevents chronic inflammation and fibrosis, and promotes tissue repair in a rat model of postoperative pain

This study evaluated the effects of previous exposure to Transcranial Direct Current Stimulation (tDCS) on nociceptive, neuroinflammatory, and neurochemical parameters, in rats subjected to an incisional pain model. Forty adult male Wistar rats (60 days old; weighing ∼ 250 g) were divided into five groups: 1. control (C); 2. drugs (D); 3. surgery (S); 4. surgery + sham-tDCS (SsT) and 5. surgery + tDCS (ST). Bimodal tDCS (0.5 mA) was applied for 20 min/day/8 days before the incisional model. Mechanical allodynia (von Frey) was evaluated at different time points after surgery. Cytokines and BDNF levels were evaluated in the cerebral cortex, hippocampus, brainstem, and spinal cord. Histology and activity of myeloperoxidase (MPO) and N-acetyl-β-D-glucosaminidase (NAGase) were evaluated in the surgical lesion sites in the right hind paw. The results demonstrate that the surgery procedure increased BDNF and IL-6 levels in the spinal cord levels in the hippocampus, and decreased IL-1β and IL-6 levels in the cerebral cortex, IL-6 levels in the hippocampus, and IL-10 levels in the brainstem and hippocampus. In addition, preemptive tDCS was effective in controlling postoperative pain, increasing BDNF, IL-6, and IL-10 levels in the spinal cord and brainstem, increasing IL-1β in the spinal cord, and decreasing IL-6 levels in the cerebral cortex and hippocampus, IL-1β and IL-10 levels in the hippocampus. Preemptive tDCS also contributes to tissue repair, preventing chronic inflammation, and consequent fibrosis. Thus, these findings imply that preemptive methods for postoperative pain management should be considered an interesting pain management strategy, and may contribute to the development of clinical applications for tDCS in surgical situations.

When blood pressure refuses to budge: exploring the complexity of resistant hypertension

Resistant hypertension, defined as blood pressure that remains above goal despite using three or more antihypertensive medications, including a diuretic, affects a significant proportion of the hypertensive population and is associated with increased cardiovascular morbidity and mortality. Despite the availability of a wide range of pharmacological therapies, achieving optimal blood pressure control in patients with resistant hypertension remains a significant challenge. However, recent advances in the field have identified several promising treatment options, including spironolactone, mineralocorticoid receptor antagonists, and renal denervation. In addition, personalized management approaches based on genetic and other biomarkers may offer new opportunities to tailor therapy and improve outcomes. This review aims to provide an overview of the current state of knowledge regarding managing resistant hypertension, including the epidemiology, pathophysiology, and clinical implications of the condition, as well as the latest developments in therapeutic strategies and future prospects.

Probing the Promises of Noninvasive Transcranial Electrical Stimulation for Boosting Mental Performance in Sports

While the importance of physical abilities is noncontested to perform in elite sport, more focus has recently been turned toward cognitive processes involved in sport performance. Practicing any sport requires a high demand of cognitive functioning including, but not limited to, decision-making, processing speed, working memory, perceptual processing, motor functioning, and attention. Noninvasive transcranial electrical stimulation (tES) has recently attracted considerable scientific interest due to its ability to modulate brain functioning. Neuromodulation apparently improves cognitive functions engaged in sports performance. This opinion manuscript aimed to reveal that tES is likely an adjunct ergogenic resource for improving cognitive processes, counteracting mental fatigue, and managing anxiety in elite athletes. Nevertheless, the first evidence is insufficient to guarantee its real effectiveness and benefits. All tES techniques could be add-ons to make performance-related cognitive functions more efficient and obtain better results. Modulating inhibitory control through tES over the frontal cortex might largely contribute to the improvement of mental performance. Nevertheless, studies in elite athletes are required to assess the long-term effects of tES application as an ergogenic aid in conjunction with other training methods (e.g., neurofeedback, mental imagery) where cognitive abilities are trainable.

Neuromodulation Strategies to Reduce Inflammation and Improve Lung Complications in COVID-19 Patients

Since the outbreak of the COVID-19 pandemic, races across academia and industry have been initiated to identify and develop disease modifying or preventative therapeutic strategies has been initiated. The primary focus has been on pharmacological treatment of the immune and respiratory system and the development of a vaccine. The hyperinflammatory state (“cytokine storm”) observed in many cases of COVID-19 indicates a prognostically negative disease progression that may lead to respiratory distress, multiple organ failure, shock, and death. Many critically ill patients continue to be at risk for significant, long-lasting morbidity or mortality. The human immune and respiratory systems are heavily regulated by the central nervous system, and intervention in the signaling of these neural pathways may permit targeted therapeutic control of excessive inflammation and pulmonary bronchoconstriction. Several technologies, both invasive and non-invasive, are available and approved for clinical use, but have not been extensively studied in treatment of the cytokine storm in COVID-19 patients. This manuscript provides an overview of the role of the nervous system in inflammation and respiration, the current understanding of neuromodulatory techniques from preclinical and clinical studies and provides a rationale for testing non-invasive neuromodulation to modulate acute systemic inflammation and respiratory dysfunction caused by SARS-CoV-2 and potentially other pathogens. The authors of this manuscript have co-founded the International Consortium on Neuromodulation for COVID-19 to advocate for and support studies of these technologies in the current coronavirus pandemic.

Effect of Transcranial Pulsed Current Stimulation on Fatigue Delay after Medium-Intensity Training

The purpose of this study was to investigate the effect of transcranial pulsed current stimulation (tPCS) on fatigue delay after medium-intensity training. Materials and Methods: Ninety healthy college athletes were randomly divided into an experimental group (n = 45) and control group (n = 45). The experimental group received medium-intensity training for a week. After each training, the experimental group received true stimulation of tPCS (continuous 15 min 1.5 mA current intensity stimulation). The control group received sham stimulation. The physiological and biochemical indicators of participants were tested before and after the experiment, and finally 30 participants in each group were included for data analysis. Results: In the experimental group, creatine kinase (CK), cortisol (C), time-domain heart rate variability indices root mean square of the successive differences (RMSSD), standard deviation of normal R-R intervals (SDNN), and frequency domain indicator low frequency (LF) all increased slowly after the intervention. Among these, CK, C, and SDNN values were significantly lower than those in the control group (p < 0.05). Testosterone (T), T/C, and heart rate variability frequency domain indicator high frequency (HF) in the experimental group decreased slowly after the intervention, and the HF value was significantly lower than that in the control group (p < 0.05). The changes in all of the indicators in the experimental group were smaller than those in the control group. Conclusion: The application of tPCS after medium-intensity training enhanced the adaptability to training and had a significant effect on the maintenance of physiological state. The application of tPCS can significantly promote the recovery of autonomic nervous system function, enhance the regulation of parasympathetic nerves, and delay the occurrence of fatigue.

Autonomic Neural Circuit and Intervention for Comorbidity Anxiety and Cardiovascular Disease

Anxiety disorder is a prevalent psychiatric disease and imposes a significant influence on cardiovascular disease (CVD). Numerous evidence support that anxiety contributes to the onset and progression of various CVDs through different physiological and behavioral mechanisms. However, the exact role of nuclei and the association between the neural circuit and anxiety disorder in CVD remains unknown. Several anxiety-related nuclei, including that of the amygdala, hippocampus, bed nucleus of stria terminalis, and medial prefrontal cortex, along with the relevant neural circuit are crucial in CVD. A strong connection between these nuclei and the autonomic nervous system has been proven. Therefore, anxiety may influence CVD through these autonomic neural circuits consisting of anxiety-related nuclei and the autonomic nervous system. Neuromodulation, which can offer targeted intervention on these nuclei, may promote the development of treatment for comorbidities of CVD and anxiety disorders. The present review focuses on the association between anxiety-relevant nuclei and CVD, as well as discusses several non-invasive neuromodulations which may treat anxiety and CVD.

Acute and Short-Term Autonomic and Hemodynamic Responses to Transcranial Direct Current Stimulation in Patients With Resistant Hypertension

Previously, we demonstrated that acute transcranial direct current stimulation (tDCS) reduced blood pressure (BP) and improved autonomic modulation in hypertensives. We hypothesized that acute and short-term tDCS intervention can promote similar benefits in resistant hypertensive patients (RHT). We assessed the impact of one (acute intervention) and ten (short-term intervention) tDCS or SHAM (20 min, each) sessions on BP, pulse interval (PI) and systolic blood pressure variabilities, humoral mechanisms associated with BP regulation, and cytokines levels. True RHT subjects (n = 13) were randomly submitted to one and ten SHAM and tDCS crossing sessions (1 week of “washout”). Hemodynamic (Finometer^®, Beatscope), office BP, and autonomic variables (accessed through spectral analysis of the pulse-to-pulse BP signal, in the time and frequency domain – Fast Fourrier Transform) were measured at baseline and after the short-term intervention. 24 h-ambulatory BP monitoring was measured after acute and short-term protocols. Acute intervention: tDCS reduced BP, cardiac output, and increase high-frequency band of PI (vagal modulation to the heart). Short-term protocol: tDCS did not change BP and cardiac output parameters. In contrast, central systolic BP (−12%), augmentation index (−31%), and pulse wave velocity (34%) were decreased by the short-term tDCS when compared to SHAM. These positive results were accompanied by a reduction in the low-frequency band (−37%) and an increase of the high-frequency band of PI (+62%) compared to SHAM. These findings collectively indicate that short-term tDCS concomitantly improves resting cardiac autonomic control and pulse wave behavior and reduces central BP in RHT patients, https://ensaiosclinicos.gov.br/rg/RBR-8n7c9p.

Modulating eating behavior with transcranial direct current stimulation (tDCS): A systematic literature review on the impact of eating behavior traits

Transcranial direct current stimulation (tDCS) is becoming an increasingly popular technique for altering eating behaviors. Recent research suggests a possible eating behavior trait-dependent effect of tDCS. However, studies recruit participant populations with heterogeneous trait characteristics, including "healthy" individuals who do not present with eating behavior traits suggesting susceptibility to overconsumption. The present review considers the effects of tDCS across eating-related measures and explores whether a trait-dependent effect is evident across the literature. A literature search identified 28 articles using sham-controlled tDCS to modify eating-related measures. Random effects meta-analyses were performed, with subgroup analyses to identify differences between "healthy" and trait groups. Trivial overall effects (g = -0.12 to 0.09) of active versus sham tDCS were found. Subgroup analyses showed a more consistent effect for trait groups, with small and moderate effect size (g = -1.03 to 0.60), suggesting tDCS is dependent on participants' eating behavior traits. Larger effect sizes were found for those displaying traits associated with study outcomes (e.g., heightened food cravings). "Healthy" individuals appear to be unresponsive to stimulation. Based on this meta data, future work should recruit those with eating behavior trait susceptibilities to overconsumption, focusing on those who present with traits associated with the outcome of interest.

ACUTE TRANSCRANIAL DIRECT CURRENT STIMULATION (tDCS) IMPROVES VENTILATORY VARIABILITY AND AUTONOMIC MODULATION IN RESISTANT HYPERTENSIVE PATIENTS

Here, we assessed the impact of one session of transcranial direct current stimulation (tDCS) or SHAM (20 min, each) on ventilatory responses to cardiopulmonary exercise test, central and peripheral blood pressure (BP), and autonomic modulation in resistant hypertensive (RHT) patients. RHT subjects (n = 13) were randomly submitted to SHAM and tDCS crossing sessions (1 week of "washout"). Patients and a technician who set the tDCS/Sham room up were both blind. After brain stimulation, patients were submitted to a cardiopulmonary exercise test to evaluate ventilatory and cardiovascular response to exercise. Hemodynamic (Finometer®, Beatscope), and autonomic variables were measured at baseline (before tDCS/Sham) and after incremental exercise. RESULTS: Our study shows that tDCS condition improved heart rate recovery, VO2 peak, and vagal modulation (after cardiopulmonary exercise test); attenuated the ventilatory variability response, central and peripheral blood pressure well as sympathetic modulation (after cardiopulmonary exercise test) in comparison with SHAM. These data suggest that acute tDCS sessions prevented oscillatory ventilation behavior during the cardiopulmonary exercise test and mitigated the increase of systolic blood pressure in RHT patients. After the exercise test, tDCS promotes better vagal reentry and improved autonomic modulation, possibly reducing central blood pressure and aortic augmentation index compared to SHAM. Brazilian Registry of Clinical Trials (ReBEC): https://ensaiosclinicos.gov.br/rg/RBR-8n7c9p.

Effects of transcranial direct current stimulation associated with an aerobic exercise bout on blood pressure and autonomic modulation of hypertensive patients: A pilot randomized clinical trial

The objective of this article was to evaluate the effects of an aerobic exercise bout associated with a single session of anodal transcranial direct current stimulation (tDCS) over the left temporal lobe on blood pressure (BP) and heart rate variability (HRV) in hypertensive people. After met the inclusion criteria, twenty hypertensive people were randomized to active-tDCS or sham-tDCS group. Initially, they provided their sociodemographic data, a blood sample, and went through an evaluation of the cardiorespiratory performance. Then, a single session of tDCS with an intensity of 2 mA over the left lobe during 20 min was carried out. After tDCS, it was performed a session of moderate-intensity aerobic exercise during 40 min. BP during 24 h and HRV measurements were performed before (baseline) and after the intervention. Systolic BP during sleep time decreased in the active-tDCS group (p = 0.008). Diastolic BP showed a significant decrease 3 h after the intervention in the active-tDCS group (p = 0.01). An intragroup comparison showed a significant decrease in systolic BP 3 h after intervention only for the active-tDCS group (p = 0.04). Besides, there was a trend toward a difference in wake for diastolic BP for active-tDCS (p = 0.07). Lastly, there were no changes in the HRV for both groups. It is suggested that anodal tDCS associated with moderate-intensity aerobic exercise can decrease systolic and diastolic BP of hypertensive people during sleep time and 3 h after the intervention.

Effect of tDCS on well-being and autonomic function in professional male players after official soccer matches

This study aimed to examine the effect of transcranial direct current stimulation (tDCS) used as a recovery strategy, on heart rate (HR) measures and perceived well-being in 12 male professional soccer players. tDCS was applied in the days after official matches targeting the left dorsolateral prefrontal cortex (DLPFC) with 2 mA for 20 min (F3-F4 montage). Participants were randomly assigned to anodal tDCS (a-tDCS) or sham tDCS sessions. Players completed the Well-Being Questionnaire (WBQ) and performed the Submaximal Running Test (SRT) before and after tDCS. HR during exercise (HRex) was determined during the last 30 s of SRT. HR recovery (HRR) was recorded at 60 s after SRT. The HRR index was calculated from the absolute difference between HRex and HRR. A significant increase was observed for WBQ (effect of time; p<0.001; η_p²=0.417) with no effect for condition or interaction. A decrease in HRR (p = 0.014; η_p²=0.241), and an increase in HRR index were observed (p = 0.045; η_p²=0.168), with no effect for condition or interaction. No change for HRex was evident (p>0.05). These results suggest that a-tDCS over the DLPFC may have a positive effect on enhancing well-being and parasympathetic autonomic markers, which opens up a possibility for testing tDCS as a promising recovery-enhancing strategy targeting the brain in soccer players. The findings suggest that brain areas related to emotional and autonomic control might be involved in these changes with a possible interaction effect of tDCS by placebo-related effects, but more research is needed to verify this effect.

Applications of Non-invasive Neuromodulation for the Management of Disorders Related to COVID-19

Background: Novel coronavirus disease (COVID-19) morbidity is not restricted to the respiratory system, but also affects the nervous system. Non-invasive neuromodulation may be useful in the treatment of the disorders associated with COVID-19. Objective: To describe the rationale and empirical basis of the use of non-invasive neuromodulation in the management of patients with COVID-10 and related disorders. Methods: We summarize COVID-19 pathophysiology with emphasis of direct neuroinvasiveness, neuroimmune response and inflammation, autonomic balance and neurological, musculoskeletal and neuropsychiatric sequela. This supports the development of a framework for advancing applications of non-invasive neuromodulation in the management COVID-19 and related disorders. Results: Non-invasive neuromodulation may manage disorders associated with COVID-19 through four pathways: (1) Direct infection mitigation through the stimulation of regions involved in the regulation of systemic anti-inflammatory responses and/or autonomic responses and prevention of neuroinflammation and recovery of respiration; (2) Amelioration of COVID-19 symptoms of musculoskeletal pain and systemic fatigue; (3) Augmenting cognitive and physical rehabilitation following critical illness; and (4) Treating outbreak-related mental distress including neurological and psychiatric disorders exacerbated by surrounding psychosocial stressors related to COVID-19. The selection of the appropriate techniques will depend on the identified target treatment pathway. Conclusion: COVID-19 infection results in a myriad of acute and chronic symptoms, both directly associated with respiratory distress (e.g., rehabilitation) or of yet-to-be-determined etiology (e.g., fatigue). Non-invasive neuromodulation is a toolbox of techniques that based on targeted pathways and empirical evidence (largely in non-COVID-19 patients) can be investigated in the management of patients with COVID-19.

Update on the Use of Transcranial Electrical Brain Stimulation to Manage Acute and Chronic COVID-19 Symptoms

The coronavirus disease 19 (COVID-19) pandemic has resulted in the urgent need to develop and deploy treatment approaches that can minimize mortality and morbidity. As infection, resulting illness, and the often prolonged recovery period continue to be characterized, therapeutic roles for transcranial electrical stimulation (tES) have emerged as promising non-pharmacological interventions. tES techniques have established therapeutic potential for managing a range of conditions relevant to COVID-19 illness and recovery, and may further be relevant for the general management of increased mental health problems during this time. Furthermore, these tES techniques can be inexpensive, portable, and allow for trained self-administration. Here, we summarize the rationale for using tES techniques, specifically transcranial Direct Current Stimulation (tDCS), across the COVID-19 clinical course, and index ongoing efforts to evaluate the inclusion of tES optimal clinical care.

Effects of transcranial direct current stimulation on heart rate variability: a systematic review protocol

OBJECTIVE

This systematic review aims to synthesize the available evidence on the effects of transcranial direct current stimulation on heart rate modulation, indexed by heart rate variability parameters in healthy individuals and those with clinical disorders.

INTRODUCTION

There is some evidence that altered heart rate variability parameters are associated with different clinical disorders. For example, diminished parasympathetic activity has been explored as a potential biomarker for some chronic pain conditions. Considering the dynamic interaction between brain and heart, neuromodulatory strategies targeting this relationship could exert a positive influence on the cardiac autonomic system. Transcranial direct current stimulation is a non-invasive neuromodulation technique that has been presenting recent advances in the treatment of various clinical disorders. However, the evidence concerning transcranial direct current stimulation application focusing on brain-heart interaction is still controversial.

INCLUSION CRITERIA

This review will consider studies that investigate the effects of transcranial direct current stimulation on heart rate variability in healthy participants or those with clinical disorders.

METHODS

This review will follow JBI systematic review methodology recommendations. PubMed, Embase, CINAHL, Web of Science, PsycNET, Cochrane Controlled Register of Trials (CENTRAL) and Physiotherapy Evidence Database (PEDro) will be searched, along with several sources of gray literature. Retrieval of full-text studies, and assessment of methodological quality and data extraction, will be performed independently by two reviewers. Data will be pooled in statistical meta-analysis, where possible.

SYSTEMATIC REVIEW REGISTRATION NUMBER

PROSPERO CRD42018114105.

Transcranial Direct Current Stimulation: No Effect on Aerobic Performance, Heart Rate, or Rating of Perceived Exertion in a Progressive Taekwondo-Specific Test

PURPOSE

To investigate the effects of anodal transcranial direct current stimulation (a-tDCS) on the aerobic performance, heart rate (HR), and rating of perceived exertion (RPE) of highly trained taekwondo athletes.

METHODS

Twelve (8 men and 4 women) international/national-level athletes received a-tDCS or sham treatment over the M1 location in a randomized, single-blind crossover design. The stimulation was delivered at 1.5 mA for 15 min using an extracephalic bihemispheric montage. Athletes performed the progressive-specific taekwondo test 10 min after stimulation. HR was monitored continuously during the test, and RPE was registered at the end of each stage and at test cessation.

RESULTS

There were no significant differences between sham and a-tDCS in time to exhaustion (14.6 and 14.9, respectively, P = .53, effect size = 0.15) and peak kicking frequency (52 and 53.6, respectively, P = .53, effect size = 0.15) or in HR (P > .05) and RPE responses (P > .05).

CONCLUSIONS

Extracephalic bihemispheric a-tDCS over M1 did not influence the aerobic performance of taekwondo athletes or their psychophysiological responses, so athletes and staff should be cautious when using it in a direct-to-consumer manner.

Neurostimulation, doping, and the spirit of sport

There is increasing interest in using neuro-stimulation devices to achieve an ergogenic effect in elite athletes. Although the World Anti-Doping Authority (WADA) does not currently prohibit neuro-stimulation techniques, a number of researchers have called on WADA to consider its position on this issue. Focusing on trans-cranial direct current stimulation (tDCS) as a case study of an imminent so-called ‘neuro-doping’ intervention, we argue that the emerging evidence suggests that tDCS may meet WADA’s own criteria (pertaining to safety, performance-enhancing effect, and incompatibility with the ‘spirit of sport’) for a method’s inclusion on its list of prohibited substances and methods. We begin by surveying WADA’s general approach to doping, and highlight important limitations to the current evidence base regarding the performance-enhancing effect of pharmacological doping substances. We then review the current evidence base for the safety and efficacy of tDCS, and argue that despite significant shortcomings, there may be sufficient evidence for WADA to consider prohibiting tDCS, in light of the comparable flaws in the evidence base for pharmacological doping substances. In the second half of the paper, we argue that the question of whether WADA ought to ban tDCS turns significantly on the question of whether it is compatible with the ‘spirit of sport’ criterion. We critique some of the previously published positions on this, and advocate our own sport-specific and application-specific approach. Despite these arguments, we finally conclude by suggesting that tDCS ought to be monitored rather than prohibited due to compelling non-ideal considerations.

Effects of Transcranial Direct Current Stimulation (tDCS) and Exercises Treadmill on Autonomic Modulation of Hemiparetic Patients Due To Stroke-Clinic Test, Controlled, Randomized, Double-Blind

Background: After a Stroke, there is an autonomic nervous system (ANS) changes. Transcranial Direct Current Stimulation (tDCS) can promote the reorganization of the affected circuits.

Objective: To evaluate the effects of tDCS applied before a session of physical activity on the treadmill, in the modulation of the autonomic nervous system of post-stroke patients.

Methodology: Cross-over study, were randomized 12 adult hemiparetic subjects in 2 groups, Group 1 (active tDCS before exercise on the treadmill) and Group 2 (sham tDCS before exercise on the treadmill). Stimulation times were 20 min; treadmill time was 20 min. The heart rate variability (HRV) and Variability of Systolic Blood Pressure (VSBP) were evaluated for 15 min, in 3 periods (pre and post tDCS and during exercise recovery on the treadmill).

Results: There was no difference in the VSBP and the HRV between the groups, compared with the baseline data; however, in the intragroup analysis, the parasympathetic modulation after active tDCS increased by 18% over baseline by the RMSSD with IC 95% (−7.85 to −0.34). In group 1, the post-tDCS active and post-exercise periods presented a value of variance above baseline, indicating a better prognosis. In group 2, there was a significant reduction of 38% of Variance values (p = 0.003) after tDCS sham.

Conclusion: tDCS does not generate immediate effects on HRV and VSBP, except for intragroup comparison, which has greater participation in parasympathetic modulation in the group receiving active tDCS.

Targeting the Autonomic Nervous System Balance in Patients with Chronic Low Back Pain Using Transcranial Alternating Current Stimulation: A Randomized, Crossover, Double-Blind, Placebo-Controlled Pilot Study

Background

Chronic low back pain (CLBP) is characterized by an alteration in pain processing by the central nervous system that may affect autonomic nervous system (ANS) balance. Heart rate variability (HRV) reflects the balance of parasympathetic and sympathetic ANS activation. In particular, respiratory sinus arrhythmia (RSA) solely reflects parasympathetic input and is reduced in CLBP patients. Yet, it remains unknown if non-invasive brain stimulation can alter ANS balance in CLBP patients.

Objective

To evaluate if non-invasive brain stimulation modulates the ANS, we analyzed HRV metrics collected in a previously published study of transcranial alternating current stimulation (tACS) for the modulation of CLBP through enhancing alpha oscillations. We hypothesized that tACS would increase RSA.

Methods

A randomized, crossover, double-blind, sham-controlled pilot study was conducted to investigate the effects of 10Hz-tACS on metrics of ANS balance calculated from electrocardiogram (ECG). ECG data were collected for 2 mins before and after 40 mins of 10Hz-tACS or sham stimulation.

Results

There were no significant changes in RSA or other frequency-domain HRV components from 10Hz-tACS. However, exploratory time-domain HRV analyses revealed a significant increase in the standard deviation of normal intervals between R-peaks (SDNN), a measure of ANS balance, for 10Hz-tACS relative to sham.

Conclusion

Although tACS did not significantly increase RSA, we found in an exploratory analysis that tACS modulated an integrated HRV measure of both ANS branches. These findings support the further study of how the ANS and alpha oscillations interact and are modulated by tACS.

ClinicalTrials.gov

Transcranial Alternating Current Stimulation in Back Pain – Pilot Study, NCT03243084.

Transcranial Direct Current Stimulation of the Temporal Lobe Does Not Affect High-Intensity Work Capacity

Ciccone, AB, Deckert, JA, Schlabs, CR, Tilden, MJ, Herda, TJ, Gallagher, PM, and Weir, JP. Transcranial direct current stimulation of the temporal lobe does not affect high-intensity work capacity. J Strength Cond Res 33(8): 2074-2086, 2019-Stimulation of the left insular cortex may affect heart rate variability (HRV) and exercise effort perception. These studies investigated the effects transcranial direct current stimulation (tDCS) and electrode orientation on HRV and repeated maximal knee extensions. In study 1, after sham stimulation, anodal left temporal lobe stimulation, or anodal right temporal lobe stimulation, 10 male and 10 female subjects (age = 21.0 ± 1.5 years) completed 50 maximum isokinetic extensions at 180°·s. There was a significant effect of stimulation condition on HRV for only 1 (SD2; p = 0.037; η = 0.159) of 5 HRV metrics. There was no significant effect on isokinetic fatigue percent or isokinetic work (all p ≥ 0.278; all η ≤.065). It has been proposed that placing the cathode electrode on the shoulder may differentially affect tDCS. Therefore, in study 2, the effects of electrode orientation on tDCS-induced changes in HRV was assessed in 10 healthy females and 8 healthy males (21.6 ± 2.5 years) who completed cephalic, extracephalic, and sham trials. In the cephalic montage, the anode was placed over the left temporal lobe and the cathode was placed over right prefrontal cortex. In the extracephalic montage, the cathode was placed on the shoulder on the same side of the body as the anode. Neither cephalic nor extracephalic montages affected HRV (all p ≥ 0.152; all η ≤.105). These data suggest that anodal tDCS of the insular cortex has little effect on HRV, and does not improve high-intensity exercise performance in the current population. Therefore, anodal tDCS applied over the left temporal lobe is not recommended for high-intensity performance enhancement.

TRANSCRANIAL DIRECT-CURRENT STIMULATION IN COMBINATION WITH EXERCISE: A SYSTEMATIC REVIEW

ABSTRACT Introduction Transcranial direct-current stimulation (tDCS) is a noninvasive technique that allows the modulation of cortical excitability and can produce changes in neuronal plasticity. The application of tDCS has recently been associated with physical activity. Objectives To verify the effect of Transcranial Direct-Current Stimulation (tDCS) in combination with physical exercise, characterizing methodological aspects of the technique. Methods In the database search, studies with animals, other neuromodulation techniques and opinion and review articles were excluded. Publications up to 2016 were selected and the methodological quality of the articles was verified through the PEDro scale. Results The majority of studies (86%) used tDCS on the motor cortex area, with anodal current and the allocation of monocephalic electrodes (46.5%). The prevalent current intensity was 2mA (72%), with duration of 20min (55.8%). The profile of the research participants was predominantly of subjects aged up to 60 years (72.1%). The outcomes were favorable for the use of anodal tDCS in combination with physical exercise. Conclusion Transcranial Direct-Current Stimulation is a promising technique when used in combination with aerobic and anaerobic exercises; however, it is necessary to investigate concurrent exercise. Level of Evidence II; Therapeutic Studies Investigating the Results of Treatment (systematic review of Level II studies or Level I studies with inconsistent results).

Beyond the target area: an integrative view of tDCS-induced motor cortex modulation in patients and athletes

Transcranial Direct Current Stimulation (tDCS) is a non-invasive technique used to modulate neural tissue. Neuromodulation apparently improves cognitive functions in several neurologic diseases treatment and sports performance. In this study, we present a comprehensive, integrative review of tDCS for motor rehabilitation and motor learning in healthy individuals, athletes and multiple neurologic and neuropsychiatric conditions. We also report on neuromodulation mechanisms, main applications, current knowledge including areas such as language, embodied cognition, functional and social aspects, and future directions. We present the use and perspectives of new developments in tDCS technology, namely high-definition tDCS (HD-tDCS) which promises to overcome one of the main tDCS limitation (i.e., low focality) and its application for neurological disease, pain relief, and motor learning/rehabilitation. Finally, we provided information regarding the Transcutaneous Spinal Direct Current Stimulation (tsDCS) in clinical applications, Cerebellar tDCS (ctDCS) and its influence on motor learning, and TMS combined with electroencephalography (EEG) as a tool to evaluate tDCS effects on brain function.

Postexercise blood pressure and autonomic responses after aerobic exercise following anodal tDCS applied over the medial prefrontal cortex

Transcranial direct current stimulation (tDCS) is acknowledged to modulate autonomic cardiac activity and hemodynamic responses at rest and during exercise. However, its potential to optimize postexercise hypotension (PEH) has not been investigated. This study investigated the effects of anodal tDCS applied over the medial prefrontal cortex (mPFC) upon blood pressure (BP) and heart rate variability (HRV) throughout 60 min following acute aerobic exercise. Fifteen young men (27.5 ± 5.2 yrs; 72.9 ± 8 kg; 170 ± 0.1 cm; 124.1 ± 1.9/67.7 ± 2.1 mmHg) underwent three counterbalanced experimental sessions: a) anodal tDCS + exercise (tDCS); b) sham stimulation + exercise (SHAM); c) non-exercise control (CONT). Exercise consisted in 50-min cycling at 65-70% heart rate reserve. BP and HRV were assessed during 60-min postexercise. Mean reduction in systolic BP occurred after tDCS vs. SHAM (-4.1 mmHg; P=0.03) and CONT (-5.8 mmHg; P=0.003), and in MAP vs. CONT (-3.0 mmHg, P=0.03). Parasympathetic activity lowered after tDCS and SHAM vs. CONT, as respectively reflected by R-R intervals (-328.1% and -396.4%; P = 0.001), SDNN (-155.7% and -193.4%; P = 0.006), and pNN50 (-272.3% and -259.1%; P = 0.021). There was a clear tendency of increased sympatho-vagal balance vs. CONT (P = 0.387) after SHAM (+246.3%), but not tDCS (+25.9%). In conclusion, an aerobic exercise bout preceded by tDCS applied over mPFC induced PEH in normotensive men. Parasympathetic activity lowered, while sympatho-vagal balance increased after both tDCS and SHAM vs. CONT. However, these responses seemed to be tempered by anodal stimulation, which might help explaining the occurrence of PEH after tDCS and not SHAM. These findings warrant further research on the role of tDCS within exercise programs aiming at BP management.

Transcranial direct current stimulation to enhance athletic performance outcome in experienced bodybuilders

Transcranial direct current stimulation (tDCS) is currently under investigation as a promising technique for enhancement of athletic performance through modulating cortical excitability. Through consecutive randomization, 12 experienced bodybuilders were randomly assigned to two arms receiving either sham or real tDCS over the primary motor cortex (leg area) and left temporal cortex (T3) for 13 minutes in the first session. After 72 hours, both groups received the inverse stimulation. After the brain stimulation, cerebral hemodynamic response (using frontopolar hemoencephalography) was examined upon taking three computer-based cognitive tasks i.e. reasoning, memory and verbal ability using the Cambridge Brain Science-Cognitive Platform. Subsequently, the bodybuilders performed knee extension exercise while performance indicators including one-repetition maximum (1RM), muscular endurance (SEI), heart rate (ECG), motivation (VAS), surface electromyography over quadriceps femoris muscle (sEMG) and perceived exertion (RPE) were evaluated. The real tDCS vs. sham group showed decreased RPE and HR mean scores by 14.2% and 4.9%, respectively. Regarding muscular strength, endurance, and electrical activity, the 1RM, SEI, and sEMG factors improved by 4.4%, 16.9%, and % 5.8, respectively. Meanwhile, compared to sham, real tDCS did not affect the athletes’ motivation. Incidentally, it turned out that subjects who underwent T3 anodal stimulation outperformed in memory (p = 0.02) and verbal functions (0.02) as well as their corresponding frontopolar hemodynamic response [(memory HEG (p = 0.001) and verbal HEG (p = 0.003)]. Our findings suggest that simultaneous tDCS-induced excitation over the M1 leg area and left temporal area may potentially improve the overall athletic performance in experienced bodybuilders (Trial registration: IRCT20181104041543N1, Registered on 4 Nov. 2018, retrospectively registered).

Is tDCS an Adjunct Ergogenic Resource for Improving Muscular Strength and Endurance Performance? A Systematic Review

Exercise performance is influenced by many physical factors, such as muscle strength and endurance. Particularly in the physical fitness and sports performance contexts, there are many types of ergogenic aids to improve muscular strength and endurance performance, with non-athletes and even athletes using illegal drugs to reach the top. Thus, the development of innovative methods to aid in exercise performance is of great interest. One such method is transcranial direct current stimulation (tDCS). A systematic search was performed on the following databases, until January 2019; PubMed/MEDLINE, SCOPUS, and Pedro database. Studies on tDCS for muscular strength and endurance performance improvement in non-athletes and athletes adults were included. We compared the effect of anodal-tDCS (a-tDCS) to a sham/control condition on the outcomes muscular strength and endurance performance. We found 26 controlled trials. No trial mentions negative side effects of the intervention. The data show differences between the studies investigating muscle strength and the studies evaluating endurance, with regard to successful use of tDCS. Studies investigating the efficiency of tDCS on improving muscular strength demonstrate positive effects of a-tDCS in 66.7% of parameters tested. In contrast, in studies evaluating the effects of a-tDCS on improving endurance performance the a-tDCS revealed a significant improvement in only 50% of parameters assessed. The majority of the data shows consistently influence of a-tDCS on muscular strength, but not to endurance performance. The results of this systematic review suggest that a-tDCS can improve muscular strength, but not to endurance performance.

[Interest of transcranial stimulation in pelvic and perineal disorders]

OBJECTIVE

The aim of this article was to describe the diagnostic and therapeutic value of transcranial stimulation in pelvic and perineal disorders.

METHODS

A literature review (Medline database and Google scholar) with no time limit was performed using keywords: "transcranial direct stimulation", "transcranial magnetic stimulation", "neurogenic bladder", "urinary incontinence", "Parkinson disease", "multiple sclerosis", "stroke", "muscle spasticity", "pelvic pain", "visceral pain".

RESULTS

Twelve articles have been selected. Transcranial magnetic or electrical stimulation is a noninvasive neuromodulation technique widely used to establish brain maps to highlight causal relationships between brain and function. Regarding pelvic-perineal disorders, repeated transcranial stimulation has shown significant effects for the treatment of overactive bladder in Parkinson's disease (P<0.05) and multiple sclerosis, but also for the treatment of refractory chronic pelvic pain (P=0.026). Finally, therapeutic effects have also been demonstrated in irritable bowel syndrome. No evidence of efficacy was found on genito-sexual disorders.

CONCLUSION

Data from the literature suggest that transcranial stimulation is a noninvasive treatment that may have a role in the management of pelvic and perineal disorders. Its promising field of action would require prospective and randomized studies on a larger scale.

Transcranial Direct Current Stimulation of motor cortex enhances running performance

Transcranial direct current stimulation (tDCS) is a technique used to modulate neuronal excitability through non-invasive brain stimulation that can enhance exercise performance. We hypothesize that tDCS would improve submaximal running time to exhaustion (TTE) and delay the increase in the rating of perceived exertion (RPE) over time. We also hypothesize that tDCS would not lead to difference in cardiorespiratory responses. We employed a randomized, single-blinded, and counterbalanced design in which 10 trained men participated. After receiving either 20 min of 1.98 mA anodal tDCS applied over the primary motor cortex (M1) or sham-operated control on separate days, participants completed a constant-load test involving running at a speed equivalent to 80% of their own maximum oxygen consumption (VO2max). During this constant-load test, RPE, heart rate (HR), VO2, pulmonary ventilation (VE), respiratory exchange ratio (RER), and ventilatory threshold (VT) were continuously monitored. TTE was recorded at the end of the test. TTEs were significantly longer in the tDCS than in the sham conditions (21.18 ± 7.13 min; 18.44 ± 6.32 min; p = 0.011). For TTE, no significant differences were found in RPE between conditions at isotime. In addition, no significant differences in HR, VO2, VE, RER, and VT were found during TTE between the two stimulation conditions at any time point. These results indicate that the application of tDCS does not induce a change of the exercise performance-related index; however, it can affect the increase of the exercise duration due to the stimuli in the M1 area.

The Effect of Anodal Transcranial Direct Current Stimulation Over Left and Right Temporal Cortex on the Cardiovascular Response: A Comparative Study

Background: Stimulation of the right and left anterior insular cortex, increases and decreases the cardiovascular response respectively, thus indicating the brain’s lateralization of the neural control of circulation. Previous experiments have demonstrated that transcranial direct current stimulation (tDCS) modulates the autonomic cardiovascular control when applied over the temporal cortex. Given the importance of neural control for a normal hemodynamic response, and the potential for the use of tDCS in the treatment of cardiovascular diseases, this study investigated whether tDCS was capable of modulating autonomic regulation.

Methods: Cardiovascular response was monitored during a post-exercise muscle ischemia (PEMI) test, which is well-documented to increase sympathetic drive. A group of 12 healthy participants performed a PEMI test in a control (Control), sham (Sham) and two different experimental sessions where the anodal electrode was applied over the left temporal cortex and right temporal cortex with the cathodal electrode placed over the contralateral supraorbital area. Stimulation lasted 20 min at 2 mA. The hemodynamic profile was measured during a PEMI test. The cardiovascular parameters were continuously measured with a transthoracic bio-impedance device both during the PEMI test and during tDCS.

Results: None of the subjects presented any side effects during or after tDCS stimulation. A consistent cardiovascular response during PEMI test was observed in all conditions. Statistical analysis did not find any significant interaction and any significant main effect of condition on cardiovascular parameters (all ps > 0.316) after tDCS. No statistical differences regarding the hemodynamic responses were found between conditions and time during tDCS stimulation (p > 0.05).

Discussion: This is the first study comparing the cardiovascular response after tDCS stimulation of left and right TC both during exercise and at rest. The results of the current study suggest that anodal tDCS of the left and right TC does not affect functional cardiovascular response during exercise PEMI test and during tDCS. In light of the present and previous findings, the effect of tDCS on the cardiovascular response remains inconclusive.

Enhancement of Mood but not Performance in Elite Athletes With Transcranial Direct-Current Stimulation

PURPOSE

To determine if transcranial direct-current stimulation (tDCS) could be effective for the enhancement of swimming performance or mood state in elite athletes.

METHODS

Eight male elite triathletes (age = 20 [2] y, maximal oxygen uptake = 71 [4] mL·kg^-1·min^-1) participated in this crossover, counterbalanced, sham-controlled, double-blind study. Participants received either actual (20 min of anodal stimulation of the motor cortex at 2 mA) or sham tDCS and performed an 800-m swimming test in which rating of perceived exertion and blood lactate response were measured. Mood state (Brunel Mood Scale) was assessed before and after each tDCS session and after the swimming test. Heart-rate variability and central nervous system readiness were assessed before and after each tDCS session. The chances of finding differences between conditions were determined using magnitude-based inferences.

RESULTS

A significant and very likely higher Brunel Mood Scale-determined vigor self-perception was found with actual tDCS after the stimulation session (-0.1 [1.2] and 2.0 [2.3] for sham and actual tDCS, respectively; P = .018, effect size = 1.14) and after exercise (-4.1 [2.9] and -0.9 [3.6] for sham and actual tDCS, respectively; P = .022, effect size = 0.98). However, likely trivial and nonsignificant (P > .05) differences were found between conditions in performance (599 [38] s and 596 [39] s, respectively). Unclear and nonsignificant differences were observed between conditions for the rest of the study end points.

CONCLUSIONS

tDCS elicited a marked increase in vigor self-perception that was maintained after exercise but failed to improve swimming performance in elite triathletes.

Effect of transcranial direct current stimulation on exercise performance: A systematic review and meta-analysis

BACKGROUND

Transcranial direct current stimulation (tDCS) has been used to improve exercise performance, though the protocols used, and results found are mixed.

OBJECTIVE

We aimed to analyze the effect of tDCS on improving exercise performance.

METHODS

A systematic search was performed on the following databases, until December 2017: PubMed/MEDLINE, Embase, Web of Science, SCOPUS, and SportDiscus. Full-text articles that used tDCS for exercise performance improvement in adults were included. We compared the effect of anodal (anode near nominal target) and cathodal (cathode near nominal target) tDCS to a sham/control condition on the outcome measure (performance in isometric, isokinetic or dynamic strength exercise and whole-body exercise).

RESULTS

22 studies (393 participants) were included in the qualitative synthesis and 11 studies (236 participants) in the meta-analysis. The primary motor cortex (M1) was the main nominal tDCS target (n = 16; 72.5%). A significant effect favoring anodal tDCS (a-tDCS) applied before exercise over M1 was found on cycling time to exhaustion (mean difference = 93.41 s; 95%CI = 27.39 s-159.43 s) but this result was strongly influenced by one study (weight = 84%), no effect was found for cathodal tDCS (c-tDCS). No significant effect was found for a-tDCS applied on M1 before or during exercise on isometric muscle strength of the upper or lower limbs. Studies regarding a-tDCS over M1 on isokinetic muscle strength presented mixed results. Individual results of studies using a-tDCS applied over the prefrontal and motor cortices either before or during dynamic muscle strength testing showed positive results, but performing meta-analysis was not possible.

CONCLUSION

For the protocols tested, a-tDCS but not c-tDCS vs. sham over M1 improved exercise performance in cycling only. However, this result was driven by a single study, which when removed was no longer significant. Further well-controlled studies with larger sample sizes and broader exploration of the tDCS montages and doses are warranted.

Deontological morality can be experimentally enhanced by increasing disgust: A transcranial direct current stimulation study

Previous studies empirically support the existence of a distinctive association between deontological (but not altruistic) guilt and both disgust and obsessive-compulsive (OC) symptoms. Given that the neural substrate underlying deontological guilt comprises brain regions strictly implicated in the emotion of disgust (i.e. the insula), the present study aimed to test the hypothesis that indirect stimulation of the insula via transcranial direct current stimulation (tDCS) would enhance disgust and morality in the deontological domain. A randomized, sham-controlled, within-subject design was used. Thirty-seven healthy individuals (25 women) underwent 15-min anodal and sham tDCS over T3 in two different days, while their heart rate (HR) was recorded to derive measures of parasympathetic nervous system activity (HR variability; HRV). After the first 10-min of sham or active tDCS stimulation, participants were asked to 1) complete a series of 6-item words that could be completed with either a disgust-related word (cleaning/dirtiness) or neutral alternatives; 2) rate how much a series of vignettes, each depicting a behavior that violated a specific moral foundation, were morally wrong. Levels of trait anxiety, depression, disgust sensitivity, scrupulosity, and altruism as well as pre- and post- stimulation momentary emotional states were assessed. Compared to the sham condition, after active stimulation of T3 a) HRV significantly increased and participants b) completed more words in terms of cleaning/dirtiness and c) reported greater subjective levels of disgust, all suggesting the elicitation of the emotion of disgust. Although the results are only marginally significant, they point to the absence of difference between the two experimental conditions for moral vignettes in the altruistic domain (i.e., animal care, emotional and physical human care), but not in the deontological domain (i.e., authority, fairness, liberty, and sacrality), where vignettes were judged as more morally wrong in the active compared to the sham condition. Moreover, scores on the OCI-R correlated with how much vignettes were evaluated as morally wrong in the deontological domain only. Results preliminarily support the association between disgust and morality in the deontological domain, with important implications for OC disorder (OCD). Future studies should explore the possibility of decreasing both disgust and morality in patients with OCD by the use of non-invasive brain stimulation techniques.

Effects of transcranial direct current stimulation on time limit and ratings of perceived exertion in physically active women

The limiting factors of maximum performance in humans have been extensively investigated. The aim of this study was to verify the acute effects of transcranial direct current stimulation on time limit (i.e., the time by which an individual is able to sustain a certain intensity of effort) at 100% of peak power (tlim@100%PP) and ratings of perceived exertion (RPE). Eleven moderately active women underwent an anthropometric evaluation and a maximal incremental test in the cycle ergometer, in order to obtain peak power (PP). At the two subsequent visits, which were separated by 48-72h, participants were randomly assigned to two experimental conditions: anodal stimulation (a-tDCS) and sham. In the a-tDCS condition, the stimulus was applied in the left dorsolateral prefrontal cortex (DLPFC), with intensity of 2mA for 20min. In the sham condition, the equipment was switched off after 30s of stimulation. Immediately after the conditions, participants performed the tlim@100%PP. Immediately after the tlim@100%PP test, the RPE scale was applied. The results demonstrated that the tlim@100%PP was higher in a-tDCS condition compared to sham condition (p=0.005). No difference was found between the conditions (a-tDCS vs sham) for the RPE (p=0.52). The anodal stimulus increased the tolerance to the exercise performed in the cycloergometer with maximum load, having some ergogenic effect in exercises of cyclic characteristics.

Combined effect of prefrontal transcranial direct current stimulation and a working memory task on heart rate variability

Prefrontal cortex activity has been associated with changes to heart rate variability (HRV) via mediation of the cortico-subcortical pathways that regulate the parasympathetic and sympathetic branches of the autonomic nervous system. Changes in HRV due to altered prefrontal cortex functioning can be predicted using the neurovisceral integration model, which suggests that prefrontal hyperactivity increases parasympathetic tone and decreases contributions from the sympathetic nervous system. Working memory (WM) tasks and transcranial direct current stimulation (tDCS) have been used independently to modulate brain activity demonstrating changes to HRV in agreement with the model. We investigated the combined effects of prefrontal tDCS and a WM task on HRV. Bifrontal tDCS was administered for 15 minutes at 2mA to 20 participants in a sham controlled, single-blind study using parallel groups. A WM task was completed by participants at three time points; pre-, during-, and post-tDCS, with resting state data collected at similar times. Frequency-domain HRV was computed for high frequency (HF; 0.15-0.4Hz) and low frequency (LF; 0.04-0.15Hz) power reflecting parasympathetic and sympathetic branch activity, respectively. Response time on the WM task, but not accuracy, improved from baseline to during-tDCS and post-tDCS with sham, but not active, stimulation. HF-HRV was significantly increased in the active tDCS group compared to sham, lasting beyond cessation of stimulation. Additionally, HF-HRV showed a task-related reduction in power during performance on the WM task. Changes in LF-HRV were moderately inversely correlated (r > 0.4) with changes in WM accuracy during and following tDCS compared to baseline levels. Stimulation of the prefrontal cortex resulted in changes to the parasympathetic branch of the nervous system in agreement with a linearly additive interpretation of effects. Sympathetic activity was not directly altered by tDCS, but was correlated with changes in WM performance. This suggests that the parasympathetic and sympathetic branches respond differentially due to similar, but distinct neural pathways. Given the ease of HRV data collection, studies of prefrontal tDCS would benefit from collection of this data as it provides unique insight into tDCS effects resulting from propagation through brain networks.

Transcranial direct current stimulation in individuals with spinal cord injury: Assessment of autonomic nervous system activity

BACKGROUND

We hypothesized in this study that transcranial direct current stimulation (tDCS) of primary motor cortex could exert top-down modulation over subcortical systems associated with autonomic control and thus be useful to revert some of the dysfunctional changes found in the autonomic nervous system (ANS) of subjects with spinal cord injuries (SCI).

OBJECTIVE

To explore the acute effect of tDCS on ANS indexed by Heart Rate Variability (HRV) in individuals with SCI and analyze whether this effect depends on the gender, degree, level and time of injury.

METHODS

In this randomized, placebo-controlled, crossover, double-blinded study, 18 adults with SCI (32.9±7.9 years old) were included; the intervention consisted of a single 12-minute session of active tDCS (anodal, 2 mA) and a control session of sham tDCS applied over Cz (bihemispheric motor cortex). HRV was calculated using spectral analysis. Low-frequency (LF), high-frequency (HF), and LF/HF ratio variables were evaluated before, during, and post tDCS.

RESULTS

A two-way repeated measures ANOVA showed that after active (anodal) stimulation, LF/HF ratio was significantly increased (P = 0.013). There was a trend for an interaction between time and stimulation for both LF and HF (P = 0.052). Paired exploratory t-tests reported effects on the difference of time [post-pre] between stimulation conditions for LF (P = 0.052), HF (P = 0.052) and LF/HF (P = 0.003).

CONCLUSION

Anodal tDCS of the motor cortex modulated ANS activity in individuals with SCI independent of gender, type and time of lesion. These changes were in the direction of normalization of ANS parameters, thus confirming our initial hypothesis that an enhancement of cortical excitability by tDCS could at least partially restore some of the dysfunctional activity in the ANS system of subjects with SCI.

Transcranial direct current stimulation improves the QT variability index and autonomic cardiac control in healthy subjects older than 60 years

Background

Noninvasive brain stimulation technique is an interesting tool to investigate the causal relation between cortical functioning and autonomic nervous system (ANS) responses.

Objective

The objective of this report is to evaluate whether anodal transcranial direct current stimulation (tDCS) over the temporal cortex influences short-period temporal ventricular repolarization dispersion and cardiovascular ANS control in elderly subjects.

Subjects and methods

In 50 healthy subjects (29 subjects younger than 60 years and 21 subjects older than 60 years) matched for gender, short-period RR and systolic blood pressure spectral variability, QT variability index (QTVI), and noninvasive hemodynamic data were obtained during anodal tDCS or sham stimulation.

Results

In the older group, the QTVI, low-frequency (LF) power expressed in normalized units, the ratio between LF and high-frequency (HF) power, and systemic peripheral resistances decreased, whereas HF power expressed in normalized units and α HF power increased during the active compared to the sham condition (P<0.05).

Conclusion

In healthy subjects older than 60 years, tDCS elicits cardiovascular and autonomic changes. Particularly, it improves temporal ventricular repolarization dispersion, reduces sinus sympathetic activity and systemic peripheral resistance, and increases vagal sinus activity and baroreflex sensitivity.