Targeted tDCS Mitigates Dual-Task Costs to Gait and Balance in Older Adults

Gray Matter Volumes Mediate the Relationship Between Disease Duration and Balance Control Performance in Chronic Ankle Instability

The relationship between structural changes in the cerebral gray matter and diminished balance control performance in patients with chronic ankle instability (CAI) has remained unclear. This paper aimed to assess the difference in gray matter volume (GMV) between participants with CAI and healthy controls (HC) and to characterize the role of GMV in the relationship between disease duration and balance performance in CAI. 42 participants with CAI and 33 HC completed the structural brain MRI scans, one-legged standing test, and Y-balance test. Regional GMV was measured by applying voxel-based morphometry methods. The result showed that, compared with HC, participants with CAI exhibited lower GMV in multiple brain regions (familywise error [FWE] corrected p < 0.021). Within CAI only, but not in HC, lower GMV in the thalamus (β = -0.53, p = 0.003) and hippocampus (β = -0.57, p = 0.001) was associated with faster sway velocity of the center of pressure (CoP) in eyes closed condition (i.e., worse balance control performance). The GMV in the thalamus (percentage mediated [PM] = 32.02%; indirect effect β = 0.119, 95% CI = 0.003 to 0.282) and hippocampus (PM = 33.71%; indirect effect β = 0.122, 95% CI = 0.005 to 0.278) significantly mediated the association between the disease duration and balance performance. These findings suggest that the structural characteristics of the supraspinal elements is critical to the maintenance of balance control performance in individuals suffering from CAI, which deserve careful consideration in the management and rehabilitation programs in this population.

Improving efficacy of repetitive transcranial magnetic stimulation for treatment of Parkinson disease gait disorders

Parkinson disease (PD) is a neurodegenerative disorder that causes motor and cognitive deficits, presenting complex challenges for therapeutic interventions. Repetitive transcranial magnetic stimulation (rTMS) is a type of neuromodulation that can produce plastic changes in neural activity. rTMS has been trialed as a therapy to treat motor and non-motor symptoms in persons with Parkinson disease (PwP), particularly treatment-refractory postural instability and gait difficulties such as Freezing of Gait (FoG), but clinical outcomes have been variable. We suggest improving rTMS neuromodulation therapy for balance and gait abnormalities in PwP by targeting brain regions in cognitive-motor control networks. rTMS studies in PwP often targeted motor targets such as the primary motor cortex (M1) or supplementary motor area (SMA), overlooking network interactions involved in posture-gait control disorders. We propose a shift in focus toward alternative stimulation targets in basal ganglia-cortex-cerebellum networks involved in posture-gait control, emphasizing the dorsolateral prefrontal cortex (dlPFC), cerebellum (CB), and posterior parietal cortex (PPC) as potential targets. rTMS might also be more effective if administered during behavioral tasks designed to activate posture-gait control networks during stimulation. Optimizing stimulation parameters such as dosage and frequency as used clinically for the treatment of depression may also be useful. A network-level perspective suggests new directions for exploring optimal rTMS targets and parameters to maximize neural plasticity to treat postural instabilities and gait difficulties in PwP.

Clinical and physiological risk factors contributing to the restricted mobility in older adults: a longitudinal analysis

BACKGROUND

Mobility limitations (e.g., using wheelchair) have been closely linked to diminished functional independence and quality of life in older adults. The regulation of mobility is pertaining to multiple neurophysiologic and sociodemographic factors. We here aimed to characterize the relationships of these factors to the risk of restricted mobility in older adults.

METHODS

In this longitudinal study, 668 older adults with intact mobility at baseline completed the baseline assessments of clinical characteristics, cognitive function, sleep quality, activities of daily living (ADL), walking performance, beat-to-beat blood pressure, and structural MRI of the brain. Then 506 of them (mean age = 70.7 ± 7.5 years) responded to the follow-up interview on the mobility limitation (as defined by if using wheelchair, cane, or walkers, or being disabled and lying on the bed) after 18 ± 3.5 months. Logistic regression analyses were performed to examine the relationships between the baseline characteristics and the follow-up mobility restriction.

RESULTS

At baseline, compared to intact-mobility group (n = 475), restricted-mobility group (n = 31) were older, with lower score of ADL and the Montreal Cognitive Assessment (MoCA), greater score of Pittsburgh Sleep Quality Index (PSQI), poorer cardio- and cerebral vascular function, and slower walking speeds (ps < 0.05). The logistic regression analysis demonstrated that participants who were with history of falls, uncontrolled-hypertension, and/or greater Fazekas scale (odds ratios (ORs):1.3 ~ 13.9, 95% confidence intervals (CIs) = 1.1 ~ 328.2), walked slower, and/or with lower ADL score (ORs: 0.0026 ~ 0.9; 95%CI: 0.0001 ~ 0.99) at baseline, would have significantly greater risk of restricted mobility (p < 0.05; VIFs = 1.2 ~ 1.9).

CONCLUSIONS

These findings provide novel profile of potential risk factors, including vascular characteristics, psycho-cognitive and motor performance, for the development of restricted mobility in near future in older adults, ultimately helping the design of appropriate clinical and rehabilitative programs for mobility in this population.

An Educational Program for Remote Training and Supervision of Home-Based Transcranial Electrical Stimulation: Feasibility and Preliminary Effectiveness

OBJECTIVES

There has been recent interest in the administration of transcranial electrical stimulation (tES) by a caregiver, family member, or patient themselves while in their own homes (HB-tES). The need to properly train individuals in the administration of HB-tES is essential, and the lack of a uniform training approach across studies has come to light. The primary aim of this paper is to present the HB-tES training and supervision program, a tele-supervised, instructional, and evaluation program to teach laypersons how to administer HB-tES to a participant and to provide a standardized framework for remote monitoring of participants by teaching staff. The secondary aim is to present early pilot data on the feasibility and effectiveness of the training portion of the program based on its implementation in 379 sessions between two pilot clinical trials.

MATERIALS AND METHODS

The program includes instructional materials, standardized tele-supervised hands-on practice sessions, and a system for remote supervision of participants by teaching staff. Nine laypersons completed the training program. Data on the feasibility and effectiveness of the program were collected.

RESULTS

No adverse events were reported during the training or any of the HB-tES sessions after the training. All laypersons successfully completed the training. The nine laypersons reported being satisfied with the training program and confident in their tES administration capabilities. This was consistent with laypersons requiring technical assistance from teaching staff very infrequently during the 379 completed sessions. The average adherence rate between all administrators was >98%, with seven of nine administrators having 100% adherence to the scheduled sessions.

CONCLUSIONS

These findings indicate that the HB-tES program is effective and is associated with participant satisfaction.

SIGNIFICANCE

We hope that the remote nature of this training program will facilitate increased accessibility to HB-tES research for participants of different demographics and locations. This program, designed for easy adaptation to different HB-tES research applications and devices, also is accessible online. The adoption of this program is expected to facilitate uniformity of study methods among future HB-tES studies and thereby accelerate the pace of tES intervention discovery.

Comparing the effects of cerebellar and prefrontal anodal transcranial direct current stimulation concurrent with postural training on balance and fatigue in patients with multiple sclerosis: a double-blind, randomized, sham-controlled trial

Fatigue and balance disorders are common challenges experienced by Multiple Sclerosis (MS) individuals. The purpose of this study was to compare the concurrent effects of cerebellar and prefrontal anodal trans-cranial direct current stimulation (a-tDCS) with postural training on balance and fatigue in MS patients. 51 patients were evaluated to randomly allocation to a-tDCS over cerebellum, a-tDCS over dorsolateral prefrontal cortex (DLPFC) and sham group. 46 individuals (n = 16 in experimental groups and n = 14 in control group) followed treatment. All the groups received 10 sessions of postural training. The experimental groups underwent a-tDCS with a current of 1.5 mA for a period of 20 min. While, in the sham group, tDCS was only activated for 30 s and then turned off. The treatment included 10 sessions for four weeks. Before and after intervention, fatigue and balance were assessed using Fatigue Severity Scale (FSS), Timed Up and Go (TUG) test and Berg Balance Score (BBS), respectively. There was found a significant reduction in fatigue in the group receiving a-tDCS over the prefrontal cortex with postural training compared to the other two groups (P < 0.001). Additionally, a significant improvement was found in balance in the group receiving a-tDCS over the cerebellum concurrent with postural training in comparison to the other two groups (P < 0.001). Besides, in the sham group, the significant results were not reported in the variables. (P > 0.001). The results demonstrated that a-tDCS enhances the effects of postural training on balance and fatigue in MS patients.

Uncorking the limitation-improving dual tasking using transcranial electrical stimulation and task training in the elderly: a systematic review

Introduction

With aging, dual task (DT) ability declines and is more cognitively demanding than single tasks. Rapidly declining DT performance is regarded as a predictor of neurodegenerative disease. Task training and non-invasive transcranial electrical stimulation (tES) are methods applied to optimize the DT ability of the elderly.

Methods

A systematic search was carried out in the PUBMED, TDCS (transcranial direct current stimulation) databases, as well as Web of Science, and a qualitative analysis was conducted in 56 included studies. Aiming to summarize the results of studies that implemented tES, task training, or the combination for improving DT ability and related performance changes in healthy elderly and geriatric patients. For different approaches, the training procedures, parameters, as well as outcomes were discussed.

Results

Task training, particularly cognitive-motor DT training, has more notable effects on improving DT performance in the elderly when compared to the neuromodulation method.

Discussion

Anodal transcranial direct current stimulation (tDCS) over the left dorsolateral prefrontal cortex (L-DLPFC), or its combination with task training could be promising tools. However, additional evidence is required from aged healthy people and patients, as well as further exploration of electrode montage.

Balance assessment under dual task conditions in patients with total knee arthroplasty: a test-retest reliability and concurrent validity study

BACKGROUND

Under dual-task (DT), functional mobility and balance testing can detect balance and mobility problems in activities of daily living, especially in situations that cannot be identified under single-task conditions.

OBJECTIVE

Determine the test-retest reliability and concurrent validity of the Four Square Step Test (FSST) under DT conditions for people with total knee arthroplasty (TKA).

METHOD

A total of 30 patients with TKA participated in this research, and patients were tested with the FSST under DT conditions. In addition, concurrent validity of the dual-task FSST was calculated using Timed Up and Go (TUG) under the single-task condition and Hospital for Special Surgery (HSS) Knee Score. Patients performed two FSST trials on the same day under DT conditions.

RESULTS

The intraclass correlation coefficients (ICC2,1) two-way random effects model, and minimal detectable changes with 95% confidence intervals (MDC95) values of the FSST under DT conditions were .97 and 3.43, respectively. The Pearson's correlation coefficient of the FSST with the TUG and HSS was .65 and -.40, respectively.

CONCLUSION

The FSST has been found to be a reliable and valid clinical assessment tool for dynamic balance under DT conditions in patients with TKA. For identify balance disorders in daily life at early points, clinicians and researchers can use the FSST under DT conditions in TKA.

CLINICAL TRIAL REGISTRATION NUMBER

NCT06108466.

Can transcranial direct current stimulation combined with interactive computerized cognitive training boost cognition and gait performance in older adults with mild cognitive impairment? a randomized controlled trial

BACKGROUND

Older adults with Mild Cognitive Impairment (MCI) are often subject to cognitive and gait deficits. Interactive Computerized Cognitive Training (ICCT) may improve cognitive function; however, the effect of such training on gait performance is limited. Transcranial Direct Current Stimulation (tDCS) improves cognition and gait performance. It remains unclear whether combining tDCS with ICCT produces an enhanced synergistic effect on cognition and complex gait performance relative to ICCT alone. This study aimed to compare the effects of tDCS combined with ICCT on cognition and gait performance in older adults with MCI.

METHOD

Twenty-one older adults with MCI were randomly assigned to groups receiving either anodal tDCS and ICCT ( tDCS + ICCT ) or sham tDCS and ICCT ( sham + ICCT ). Participants played Nintendo Switch cognitive games for 40 min per session, simultaneously receiving either anodal or sham tDCS over the left dorsolateral prefrontal cortex for the first 20 min. Cognitive and gait assessments were performed before and after 15 training sessions.

RESULTS

The global cognition, executive function, and working-memory scores improved in both groups, but there were no significant interaction effects on cognitive outcomes. Additionally, the group × time interactions indicated that tDCS + ICCT significantly enhanced dual-task gait performance in terms of gait speed (p = 0.045), variability (p = 0.016), and dual-task cost (p = 0.039) compared to sham + ICCT.

CONCLUSION

The combined effect of tDCS and ICCT on cognition was not superior to that of ICCT alone; however, it had a significant impact on dual-task gait performance. Administering tDCS as an adjunct to ICCT may thus provide additional benefits for older adults with MCI.

TRIAL REGISTRATION

This trial was registered at http://www.

CLINICALTRIALS

in.th/ (TCTR 20,220,328,009).

The effect of transcranial direct current stimulation associated with video game training on the postural balance of older women in the community: A blind, randomized, clinical trial

BACKGROUND

Falls are frequent in older adults and can cause trauma, injury, and death. Fall prevention with virtual reality presents good results in improving postural control. Transcranial Direct Current Stimulation (tDCS) has been used with the same aim; however, the combination of the two techniques has still been little studied.

PURPOSE

To assess whether tDCS can enhance the effect of video game training (VGT) on improving the postural balance of healthy older women.

METHOD

A blinded, randomized, controlled clinical trial was conducted with 57 older women who were randomized to three balance training groups: Control Group (VGT), Anodal Group (VGT combined with anodic tDCS-atDCS), and Sham Group (VGT combined with sham tDCS-stDCS). Balance training was performed twice a week for four weeks, totalizing eight 20-min sessions using VGT associated with tDCS. Postural balance was assessed pre-and post-training and 30 days after the end of the eight sessions using the Mini-Balance Evaluation Systems Test.

RESULTS

Compared to pre-intervention the Mini BEST test increased similarly in the three groups in post-intervention (control: pre 23.7 ± 2.8 to post 27.0 ± 2.2; anodal: pre 24.4 ± 1 to post 27.7 ± 0.8 and sham: pre 24.2 ± 1.9 to post 26.5 ± 1.6; p < 0.001) and follow-up (control: pre 23.7 ± 2.8 to follow-up 26.8 ± 2.3; anodal: pre 24.4 ± 1 to follow-up 27.3 ± 1.4 and sham: pre 24.2 ± 1.9 to follow-up 26.8 ± 1.5; p < 0.001).

CONCLUSION

There was an improvement in the postural balance of the three training groups that were independent of tDCS.

DISCUSSION

Some studies have shown the positive tDCS effects associated with other tasks to improve balance. However, these results convey the effects of only anodic-tDCS compared to sham-tDCS. Possibly, the effect of VGT surpassed the tDCS effects, promoting a ceiling effect from the combination of these two therapies. However, studies with other therapies combined with tDCS for older adults deserve to be investigated, as well as in frail older people.

Transcranial direct current stimulation facilitates backward walking training

Backward walking training presents a great challenge to the physical and neural systems, which may result in an improvement in gait performance. Transcranial direct current electrical stimulation (tDCS), which can non-invasively enhance cortical activity, has been reported to strengthen corticomotor plasticity. We investigated whether excitatory tDCS over the primary motor cortex (M1) or the dorsolateral prefrontal cortex (DLPFC) enhances the effects of backward walking training in healthy participants. Thirty-six healthy participants (16 men and 20 women, mean age 21.3 ± 1.4 years) participated in this study. The participants were randomly assigned to one of the three tDCS groups (M1, DLPFC, and sham). They performed 5 min of backward walking training during 15 min of tDCS. We evaluated dual-task forward and backward walking performance before and after training. Both tDCS groups increased walking speed in the backward condition, but the DLPFC group increased the dual-task backward walking speed more than the M1 group. The M1 group showed decreased gait variability in dual-task backward walking, whereas the DLPFC group showed increased gait variability. Backward walking training combined with M1 stimulation may increase the backward walking speed by reducing gait variability. Backward walking training combined with DLPFC stimulation may prioritize walking speed over gait stability. Our results indicate that backward walking training combined with tDCS may be extended to other rehabilitation methods to improve gait performance.

Feasibility and Safety of Sequential Transcranial Direct Current Stimulation and Physical Therapy in Older Adults at Risk of Falling: A Randomized Pilot Study

Objective

To establish the feasibility and safety of administering transcranial direct current stimulation (tDCS) immediately prior to physical therapy (PT) sessions in older adults at risk of falls.

Design

A pilot randomized controlled study.

Setting

Outpatient geriatric physical therapy clinic.

Participants

Ten older adults living within supportive housing facilities (86.8±7.9 y/o, 8F) were enrolled in the study.

Interventions

Participants received tDCS or sham stimulation targeting the left dorsal lateral prefrontal cortex for 20 minutes, immediately prior to up to 10 of their PT visits.

Main Outcome Measures

Feasibility, safety, and functional outcomes were reported to inform the design of a larger and more definitive trial.

Results

Six fallers (88.8±5.0 y/o, 5F) completed the study and received 82.3% of the possible stimulation sessions, suggesting adding a 20-minute session of stimulation immediately prior to PT training sessions, along with pre- and post-assessments is feasible. The blinding strategy was successful and all reported side effects were expected and transient. While feasible and safe, the trial was met with numerous challenges, including selection bias, time and energy commitment, and large variation in functional performance, that must be considered when designing and implementing larger more definitive trials.

Conclusion

This study provides preliminary evidence about the feasibility, safety, and challenges to combine PT and tDCS in very frail older adults.

Cognitive impairment is associated with gait variability and fall risk in amyotrophic lateral sclerosis

BACKGROUND

In amyotrophic lateral sclerosis (ALS), gait abnormalities contribute to poor mobility and represent a relevant risk for falls. To date, gait studies in ALS patients have focused on the motor dimension of the disease, underestimating the cognitive aspects.

METHODS

Using a wearable gait analysis device, we compared gait patterns in ambulatory ALS patients with mild cognitive impairment (ALS MCI+; n = 18), and without MCI (ALS MCI-; n = 24), and healthy subjects (HS; n = 16) under two conditions: (1) normal gait (single task) and (2) walking while counting backward (dual task). Finally, we examined if the occurrence and number of falls in the 3 months following the baseline test were related to cognition.

RESULTS

In the single task condition, ALS patients, regardless of cognition, displayed higher gait variability than HS, especially for stance and swing time (p < 0.001). The dual task condition revealed additional differences in gait variability parameters between ALS MCI+ and ALS MCI- for cadence (p = 0.005), stance time (p = 0.04), swing time (p = 0.04) and stability index (p = 0.02). Moreover, ALS MCI+ showed a higher occurrence (p = 0.001) and number of falls (p < 0.001) at the follow-up. Regression analyses demonstrated that MCI condition predicted the occurrence of future falls (β = 3.649; p = 0.01) and, together with executive dysfunction, was associated with the number of falls (cognitive impairment: β = 0.63; p < 0.001; executive dysfunction: β = 0.39; p = 0.03), regardless of motor impairment at clinical examination.

CONCLUSION

In ALS, MCI is associated with exaggerated gait variability and predicts the occurrence and number of short-term falls.

Brain Structural Correlates of Obstacle Negotiation in Mild Cognitive Impairment: Results from the Gait and Brain Study

INTRODUCTION

Mild cognitive impairment (MCI) affects obstacle negotiation capabilities, potentially increasing the risk of falls in older adults. However, it is unclear whether smaller brain volumes typically observed in older individuals with MCI are related to the observed hazardous obstacle negotiation in this population.

METHODS

A total of 93 participants (71.9 ± 5.36 years of age; MCI = 53/control = 40) from the Gait and Brain Study were analyzed. Gray matter (GM) volumes from the frontal, temporal, and parietal lobes were entered in the analysis. Gait performance was recorded using a 6-m electronic walkway during two cognitive load conditions while approaching and stepping over an obstacle: (1) single-task and (2) while counting backwards by 1s from 100 (dual-task). Anticipatory adjustments in gait performance to cross an "ad hoc" obstacle were electronically measured during pre-crossing phases: early (3 steps before the late phase) and late (3 steps before obstacle). Association between the percentage of change in average gait speed and step length from early to late (i.e., anticipatory adjustments) and GM volumes was investigated using multivariate models adjusted for potential confounders.

RESULTS

Anticipatory adjustments in gait speed (Wilks' lambda: 0.35; Eta2: 0.64; p = 0.01) and step length (Wilks' lambda: 0.33; Eta2: 0.66; p = 0.01) during dual-task conditions were globally associated with GM volumes in MCI. Individuals with MCI with smaller GM volumes in the left inferior frontal gyrus, left hippocampus, right hippocampus, and right entorhinal cortex made significantly fewer anticipatory gait adjustments prior to crossing the obstacle.

CONCLUSION

Frontotemporal atrophy may affect obstacle negotiation capabilities potentially increasing the risk of falls in MCI.

The alterations in multiple neurophysiological procedures are associated with frailty phenotype in older adults

Background

Older adults oftentimes suffer from the conditions in multiple physiologic systems, interfering with their daily function and thus contributing to physical frailty. The contributions of such multisystem conditions to physical frailty have not been well characterized.

Methods

In this study, 442 (mean age = 71.4 ± 8.1 years, 235 women) participants completed the assessment of frailty syndromes, including unintentional weight loss, exhaustion, slowness, low activity, and weakness, and were categorized into frail (≥3 conditions), pre-frail (1 or 2 conditions), and robust (no condition) status. Multisystem conditions including cardiovascular diseases, vascular function, hypertension, diabetes, sleep disorders, sarcopenia, cognitive impairment, and chronic pain were assessed. Structural equation modeling examined the interrelationships between these conditions and their associations with frailty syndromes.

Results

Fifty (11.3%) participants were frail, 212 (48.0%) were pre-frail, and 180 (40.7%) were robust. We observed that worse vascular function was directly associated with higher risk of slowness [standardized coefficient (SC) = −0.419, p &lt; 0.001], weakness (SC = −0.367, p &lt; 0.001), and exhaustion (SC = −0.347, p &lt; 0.001). Sarcopenia was associated with both slowness (SC = 0.132, p = 0.011) and weakness (SC = 0.217, p = 0.001). Chronic pain, poor sleep quality, and cognitive impairment were associated with exhaustion (SC = 0.263, p &lt; 0.001; SC = 0.143, p = 0.016; SC = 0.178, p = 0.004, respectively). The multinomial logistic regression showed that greater number of these conditions were associated with increased probability of being frail (odds ratio&gt;1.23, p &lt; 0.032).

Conclusion

These findings in this pilot study provide novel insights into how multisystem conditions are associated with each other and with frailty in older adults. Future longitudinal studies are warranted to explore how the changes in these health conditions alter frailty status.

Long-term effects of repeated multitarget high-definition transcranial direct current stimulation combined with cognitive training on response inhibition gains

Background

Few studies have investigated the effects of repeated sessions of transcranial direct current stimulation (tDCS) combined with concurrent cognitive training on improving response inhibition, and the findings have been heterogeneous in the limited research. This study investigated the long-lasting and transfer effects of 10 consecutive sessions of multitarget anodal HD-tDCS combined with concurrent cognitive training on improving response inhibition compared with multitarget stimulation or training alone.

Methods

Ninety-four healthy university students aged 18–25 were randomly assigned to undergo different interventions, including real stimulation combined with stop-signal task (SST) training, real stimulation, sham stimulation combined with SST training, and sham stimulation. Each intervention lasted 20 min daily for 10 consecutive days, and the stimulation protocol targeted right inferior frontal gyrus (rIFG) and pre-supplementary motor area (pre-SMA) simultaneously with a total current intensity of 2.5 mA. Performance on SST and possible transfer effects to Stroop task, attention network test, and N-back task were measured before and 1 day and 1 month after completing the intervention course.

Results

The main findings showed that the combined protocol and the stimulation alone significantly reduced stop-signal reaction time (SSRT) in the post-intervention and follow-up tests compared to the pre-intervention test. However, training alone only decreased SSRT in the post-test. The sham control exhibited no changes. Subgroup analysis revealed that the combined protocol and the stimulation alone induced a decrease in the SSRT of the low-performance subgroup at the post-test and follow-up test compared with the pre-test. However, only the combined protocol, but not the stimulation alone, improved the SSRT of the high-performance subgroup. The transfer effects were absent.

Conclusion

This study provides supportive evidence for the synergistic effect of the combined protocol, indicating its superiority over the single intervention method. In addition, the long-term after-effects can persist for up to at least 1 month. Our findings also provide insights into the clinical application and strategy for treating response inhibition deficits.

The Potential of Transcranial Alternating Current Stimulation to Alleviate Dual-Task Gait Costs in Older Adults: Insights from a Double-Blinded Pilot Study

BACKGROUND

The performance of an attention-demanding task while walking, i.e., dual-tasking, leads to dual-task costs (e.g., reduced gait speed) in older adults. Previous studies have shown that dual-task costs in gait are associated with future falls and cognitive decline. According to the communication through coherence hypothesis, transcranial alternating current stimulation (tACS) might help alleviate this problem.

OBJECTIVE

The aim of this study was to examine the effects of a single session of theta-tACS targeting the left fronto-parietal network (L-FPN) on dual-task walking and cognitive function compared to sham stimulation and transcranial direct current stimulation (tDCS) targeting the left dorsolateral prefrontal cortex, a node within the L-FPN.

METHODS

Twenty older adults completed a four-visit, double-blinded, within-subject, cross-over study in which usual-walking, dual-task walking, and cognitive function were evaluated before and immediately after 20 min of tACS, tDCS, or sham (order randomized) stimulation. Dual-task costs to gait speed (primary outcome) and other measures were analyzed.

RESULTS

The dual-task cost to gait speed tended to be lower (i.e., better) after tACS (p = 0.067, Cohen's d = 0.433∼small); tDCS significantly reduced this dual-task cost (p = 0.012, Cohen's d = 0.618∼medium), and sham stimulation had no effect (p = 0.467). tACS significantly reduced the dual-task cost to step length (p = 0.037, Cohen's d = 0.502∼medium); a trend was seen after tDCS (p = 0.069, Cohen's d = 0.443∼small). No statistical differences were found for other measures of gait or cognitive function.

CONCLUSIONS

The positive effects of tACS on dual-task gait speed and step length were roughly similar to those seen with tDCS. These results suggest that tACS affects the fronto-parietal network and, similar to tDCS, tACS may improve dual-tasking. Nonetheless, to achieve larger benefits and differentiate the effects of tACS and tDCS on brain function and dual-task walking in older adults, other stimulation montages and protocols should be tested.

Brain activity during dual-task standing in older adults

Background

In older adults, the extent to which performing a cognitive task when standing diminishes postural control is predictive of future falls and cognitive decline. The neurophysiology of such “dual-tasking” and its effect on postural control (i.e., dual-task cost) in older adults are poorly understood. The purpose of this study was to use electroencephalography (EEG) to examine the effects of dual-tasking when standing on brain activity in older adults. We hypothesized that compared to single-task “quiet” standing, dual-task standing would decrease alpha power, which has been linked to decreased motor inhibition, as well as increase the ratio of theta to beta power, which has been linked to increased attentional control.

Methods

Thirty older adults without overt disease completed four separate visits. Postural sway together with EEG (32-channels) were recorded during trials of standing with and without a concurrent verbalized serial subtraction dual-task. Postural control was measured by average sway area, velocity, and path length. EEG metrics included absolute alpha-, theta-, and beta-band powers as well as theta/beta power ratio, within six demarcated regions-of-interest: the left and right anterior, central, and posterior regions of the brain.

Results

Most EEG metrics demonstrated moderate-to-high between-day test–retest reliability (intra-class correlation coefficients > 0.70). Compared with quiet standing, dual-tasking decreased alpha-band power particularly in the central regions bilaterally (p = 0.002) and increased theta/beta power ratio in the anterior regions bilaterally (p < 0.001). A greater increase in theta/beta ratio from quiet standing to dual-tasking in numerous demarcated brain regions correlated with greater dual-task cost (i.e., absolute increase, indicative of worse performance) to postural sway metrics (r = 0.45–0.56, p < 0.01). Lastly, participants who exhibited greater alpha power during dual-tasking in the anterior-right (r = 0.52, p < 0.01) and central-right (r = 0.48, p < 0.01) regions had greater postural sway velocity during dual-tasking.

Conclusion

In healthy older adults, alpha power and theta/beta power ratio change with dual-task standing. The change in theta/beta power ratio in particular may be related to the ability to regulate standing postural control when simultaneously performing unrelated, attention-demanding cognitive tasks. Modulation of brain oscillatory activity might therefore be a novel target to minimize dual-task cost in older adults.

Multitarget high-definition transcranial direct current stimulation improves response inhibition more than single-target high-definition transcranial direct current stimulation in healthy participants

Prior studies have focused on single-target anodal transcranial direct current stimulation (tDCS) over the right inferior frontal gyrus (rIFG) or pre-supplementary motor area (pre-SMA) to improve response inhibition in healthy individuals. However, the results are contradictory and the effect of multitarget anodal stimulation over both brain regions has never been investigated. The present study aimed to investigate the behavioral and neurophysiological effects of different forms of anodal high-definition tDCS (HD-tDCS) on improving response inhibition, including HD-tDCS over the rIFG or pre-SMA and multitarget HD-tDCS over both areas. Ninety-two healthy participants were randomly assigned to receive single-session (20 min) anodal HD-tDCS over rIFG + pre-SMA, rIFG, pre-SMA, or sham stimulation. Before and immediately after tDCS intervention, participants completed a stop-signal task (SST) and a go/nogo task (GNG). Their cortical activity was recorded using functional near-infrared spectroscopy (fNIRS) during the go/nogo task. The results showed multitarget stimulation produced a significant reduction in stop-signal reaction time (SSRT) relative to baseline. The pre-to-post SSRT change was not significant for rIFG, pre-SMA, or sham stimulation. Further analyses revealed multitarget HD-tDCS significantly decreased SSRT in both the high-performance and low-performance subgroups compared with the rIFG condition which decreased SSRT only in the low-performance subgroup. Only the multitarget condition significantly improved neural efficiency as indexed by lower △oxy-Hb after stimulation. In conclusion, the present study provides important preliminary evidence that multitarget HD-tDCS is a promising avenue to improve stimulation efficacy, establishing a more effective montage to enhance response inhibition relative to the commonly used single-target stimulation.

Is Anodal Transcranial Direct Current Stimulation an Effective Ergogenic Technology in Lower Extremity Sensorimotor Control for Healthy Population? A Narrative Review

Anodal transcranial direct current stimulation (a-tDCS) aims to hone motor skills and improve the quality of life. However, the non-repeatability of experimental results and the inconsistency of research conclusions have become a common phenomenon, which may be due to the imprecision of the experimental protocol, great variability of the participant characteristics within the group, and the irregularities of quantitative indicators. The aim of this study systematically summarised and analysed the effect of a-tDCS on lower extremity sensorimotor control under different experimental conditions. This narrative review was performed following the PRISMA guidelines until June 2022 in Web of Science, PubMed, Science Direct, Google Scholar, and Scopus. The findings of the present study demonstrated that a-tDCS can effectively improve the capabilities of lower extremity sensorimotor control, particularly in gait speed and time-on-task. Thus, a-tDCS can be used as an effective ergogenic technology to facilitate physical performance. In-depth and rigorous experimental protocol with larger sample sizes and combining brain imaging technology to explore the mechanism have a profound impact on the development of tDCS.

Network-Based Transcranial Direct Current Stimulation May Modulate Gait Variability in Young Healthy Adults

Purpose

Previous studies have linked gait variability to resting-state functional connectivity between the dorsal attention network (DAN) and the default network (DN) in the brain. The purpose of this study was to examine the effects of a novel transcranial direct current stimulation (tDCS) paradigm designed to simultaneously facilitate the excitability of the DAN and suppress the excitability of the DN (i.e., DAN+/DN-tDCS) on gait variability and other gait characteristics in young healthy adults.

Methods

In this double-blinded randomized and sham-controlled study, 48 healthy adults aged 22 ± 2 years received one 20-min session of DAN+/DN-tDCS (n = 24) or no stimulation (the Sham group, n = 24). Immediately before and after stimulation, participants completed a gait assessment under three conditions: walking at self-selected speed (i.e., normal walking), walking as fast as possible (i.e., fast walking), and walking while counting backward (i.e., dual-task walking). Primary outcomes included gait stride time variability and gait stride length variability in normal walking conditions. Secondary outcomes include gait stride time and length variability in fast and dual-task conditions, and other gait metrics derived from the three walking conditions.

Results

Compared to the Sham group, DAN+/DN-tDCS reduced stride length variability in normal and fast walking conditions, double-limb support time variability in fast and dual-task walking conditions, and step width variability in fast walking conditions. In contrast, DAN+/DN-tDCS did not alter average gait speed or the average value of any other gait metrics as compared to the sham group.

Conclusion

In healthy young adults, a single exposure to tDCS designed to simultaneously modulate DAN and DN excitability reduced gait variability, yet did not alter gait speed or other average gait metrics, when tested just after stimulation. These results suggest that gait variability may be uniquely regulated by these spatially-distinct yet functionally-connected cortical networks. These results warrant additional research on the short- and longer-term effects of this type of network-based tDCS on the cortical control of walking in younger and older populations.

Effects of 4 Weeks of High-Definition Transcranial Direct Stimulation and Foot Core Exercise on Foot Sensorimotor Function and Postural Control

Objective: This study aimed to examine the effects of 4 weeks of high-definition transcranial direct current stimulation (HD-tDCS) and foot core exercise (FCE) on foot sensorimotor function (i.e., toe flexor strength and passive ankle kinesthesia) and postural control.

Methods: In total, 36 participants were randomly assigned into three groups as follows: HD-tDCS, FCE, and the control group. A total of 12 training sessions were performed over 4 weeks (i.e., three sessions per week) in the laboratory. The HD-tDCS group received 20-min HD-tDCS with a current density of 2 mA, and the FCE group completed short foot exercise, towel curls, toe spread and squeeze, and balance board training. Participants in the control group just maintained the activities what they usually did and did not receive any interventions. Foot muscle strength, passive ankle kinesthesia, and postural control were assessed at baseline and post-intervention.

Results: HD-tDCS induced a greater decrease in the percentage changes in the passive kinesthesia thresholds of ankle inversion (p &lt; 0.001) and eversion (p = 0.013) than the control group. Compared with the control group, a significant increase in the percentage change in the metatarsophalangeal joint flexor strength was found in the HD-tDCS group (p = 0.008) and the FCE group (p = 0.027), and a significant increase in the percentage change in toe flexor strength was observed in the FCE group (p = 0.015). Moreover, FCE induced a greater reduction in the percent changes in the medial–lateral average center of gravity sway velocity in one-leg standing with eyes open (p = 0.033) and the anteroposterior average center of gravity sway velocity in one-leg standing with eyes closed (p &lt; 0.001) than control.

Conclusion: This study demonstrated that 4 weeks of HD-tDCS and FCE induced distinct benefits on foot sensorimotor function and the standing postural control performance in healthy young adults. HD-tDCS could improve the metatarsophalangeal joint flexor strength and the passive kinesthesia thresholds of ankle inversion and eversion. Meanwhile, FCE could also enhance foot muscle strength and enhance postural control performance in one-leg standing.

Effect of Transcranial Direct Current Stimulation on Endurance Performance in Elite Female Rowers: A Pilot, Single-Blinded Study

Endurance, which is dependent at least partly upon the activation of the brain cortex, is important for performance in rowing. Transcranial direct current stimulation (tDCS) has shown benefits for endurance, but its effects on the endurance performance of elite rowing athletes are unknown, and are examined in this study. Eight elite female rowers completed 5 km of rowing on an ergometer following stimulation of the tDCS and sham over motor cortices. Each session lasted 20 min and the current was set at 2.2 mA. Time, 500 m/split, power, time corresponding to 500 m (TC500) and power corresponding to 500 m (PC500) were recorded continuously throughout the tests. No significant differences in time, 500 m/split and power were observed between baseline, tDCS and sham. Compared to the sham, tDCS induced a percentage reduction in TC500 from baseline to 2500 m and 4000 m, and a percentage increase in PC500 from baseline to 500 m, 1000 m, 1500 m, 2000 m, 2500 m, 4000 m, 4500 m and 5000 m. One-session tDCS did not have significant benefits for rowing endurance performance in elite professional rowers, and had only marginally greater efficacy compared to sham. These findings offer knowledge helpful to the design of future studies exploring the effects of tDCS on the endurance performance of elite rowers.

Transcranial Direct Current Stimulation May Reduce Prefrontal Recruitment During Dual Task Walking in Functionally Limited Older Adults – A Pilot Study

Introduction

Transcranial direct current stimulation (tDCS) targeting the left dorsolateral prefrontal cortex (dlPFC) improves dual task walking in older adults, when tested just after stimulation. The acute effects of tDCS on the cortical physiology of walking, however, remains unknown.

Methods

In a previous study, older adults with slow gait and executive dysfunction completed a dual task walking assessment before and after 20 min of tDCS targeting the left dlPFC or sham stimulation. In a subset of seven participants per group, functional near-infrared spectroscopy (fNIRS) was used to quantify left and right prefrontal recruitment defined as the oxygenated hemoglobin response to usual and dual task walking (ΔHbO2), as well as the absolute change in this metric from usual to dual task conditions (i.e., ΔHbO2_cost). Paired t-tests examined pre- to post-stimulation differences in each fNIRS metric within each group.

Results

The tDCS group exhibited pre- to post-stimulation reduction in left prefrontal ΔHbO2_cost (p = 0.03). This mitigation of dual task “cost” to prefrontal recruitment was induced primarily by a reduction in left prefrontal ΔHbO2 specifically within the dual task condition (p = 0.001), an effect that was observed in all seven participants within this group. Sham stimulation did not influence ΔHbO2_cost or ΔHbO2 in either walking condition (p > 0.35), and neither tDCS nor sham substantially influenced right prefrontal recruitment (p > 0.16).

Discussion

This preliminary fNIRS data suggests that tDCS over the left dlPFC may modulate prefrontal recruitment, as reflected by a relative reduction in the oxygen consumption of this brain region in response to dual task walking.

Transcranial Direct Current Stimulation on Different Targets to Modulate Cortical Activity and Dual-Task Walking in Individuals With Parkinson’s Disease: A Double Blinded Randomized Controlled Trial

Background

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation to modulate cortical activity for improving motor function. However, the information of tDCS stimulation on different brain regions for dual-task walking and cortical modulation in Parkinson’s disease (PD) has not yet been compared.

Objective

The objective of this study was to investigate the effects of different tDCS targets on dual-task gait performance and cortical activity in patients with PD.

Methods

A total of 36 participants were randomly assigned to primary motor cortex (M1) tDCS, dorsal lateral prefrontal cortex (DLPFC) tDCS, cerebellum tDCS, or Sham tDCS group. Each group received 20 min of tDCS stimulation, except for the Sham group. Gait performance was measured by the GAITRite system during dual-task walking and single walking. Corticomotor activity of the tibialis anterior (TA) was measured using transcranial magnetic stimulation (TMS). The functional mobility was assessed using the timed up and go (TUG) test.

Results

All participants showed no significant differences in baseline data. Following the one session of tDCS intervention, M1 (p = 0.048), DLPFC (p < 0.001), and cerebellum (p = 0.001) tDCS groups demonstrated significant improvements in dual-task gait speed compared with a pretest. The time × group interaction [F(3, 32) = 5.125, p = 0.005] was detected in dual-task walking speed. The post hoc Tukey’s test showed that the differences in gait speed were between the Sham tDCS group and the DLPFC tDCS group (p = 0.03). Moreover, DLPFC tDCS also increased the silent period (SP) more than M1 tDCS (p = 0.006) and Sham tDCS (p = 0.002).

Conclusion

The results indicate that DLPFC tDCS exerted the most beneficial effects on dual-task walking and cortical modulation in participants with PD.

Clinical trial registration

[http://www.thaiclinicaltrials.org/show/TCTR20200909005], Thai Clinical Trials Registry [TCTR20200909005].

Combining Transcranial Direct Current Stimulation With Tai Chi to Improve Dual-Task Gait Performance in Older Adults With Mild Cognitive Impairment: A Randomized Controlled Trial

Introduction: Engaging in a secondary task while walking increases motor-cognitive interference and exacerbates fall risk in older adults with mild cognitive impairment (MCI). Previous studies have demonstrated that Tai Chi (TC) may improve cognitive function and dual-task gait performance. Intriguingly, with emerging studies also indicating the potential of transcranial direct current stimulation (tDCS) in enhancing such motor-cognitive performance, whether combining tDCS with TC might be superior to TC alone is still unclear. The purpose of this study was to investigate the effects of combining tDCS with TC on dual-task gait in patients with MCI.

Materials and Methods: Twenty patients with MCI were randomly assigned to receive either anodal or sham tDCS, both combined with TC, for 36 sessions over 12 weeks. Subjects received 40 min of TC training in each session. During the first 20 min, they simultaneously received either anodal or sham tDCS over the left dorsolateral prefrontal cortex. Outcome measures included dual-task gait performance and other cognitive functions.

Results: There were significant interaction effects between groups on the cognitive dual task walking. Compared to sham, the anodal tDCS group demonstrated a greater improvement on cadence and dual task cost of speed.

Conclusion: Combining tDCS with TC may offer additional benefits over TC alone in enhancing dual-task gait performance in patients with MCI.

Clinical Trial Registration: [www.ClinicalTrials.gov], identifier [TCTR20201201007].