Introduction: Stroke survivors often have motor impairments and related functional deficits. Transcranial Electrical Stimulation (tES) is a rapidly evolving field that offers a wide range of capabilities for modulating brain function, and it is safe and inexpensive. It has the potential for widespread use for post-stroke motor recovery. Transcranial Direct Current Stimulation (tDCS), Transcranial Alternating Current Stimulation (tACS), and Transcranial Random Noise Stimulation (tRNS) are three recognized tES techniques that have gained substantial attention in recent years but have different mechanisms of action. tDCS has been widely used in stroke motor rehabilitation, while applications of tACS and tRNS are very limited. The tDCS protocols could vary significantly, and outcomes are heterogeneous. Purpose: the current review attempted to explore the mechanisms underlying commonly employed tES techniques and evaluate their prospective advantages and challenges for their applications in motor recovery after stroke. Conclusion: tDCS could depolarize and hyperpolarize the potentials of cortical motor neurons, while tACS and tRNS could target specific brain rhythms and entrain neural networks. Despite the extensive use of tDCS, the complexity of neural networks calls for more sophisticated modifications like tACS and tRNS.

Objectives: The prevalence of obesity (OB) has increased in the older adult (OA) population. However, it is not quite clear whether OB exaggerates gait instability and leads to a higher risk of falls in OAs. The first goal of this study was to investigate whether OB is associated with gait alterations and gait asymmetry in OAs. The second goal of this study was to examine relationships between various OB measures with gait measures and gait symmetry measures in OAs. Methods: A total of 30 OAs were included and categorized according to their body mass index (BMI) values into groups of persons with normal weight (NW), overweight (OW), and OB. Participants were required to complete an anthropometric assessment, a body composition assessment, and overground walking tests. Results: The group with OB had shorter swing phase, longer stance phase, and shorter single support phase than the NW group. Increased body weight, BMI, visceral adipose tissue mass, and android fat had correlations with shorter swing phase, longer stance phase, and shorter single support phase. Increased body weight and BMI had significantly positive correlations with symmetry index of knee range of motion. Conclusions: OB may impair gait automation capacity in OAs. Both body weight and BMI remain good measures in terms of establishing correlations with gait stability in OAs. However, the amount of fat mass surrounding the abdomen could be vital to interpreting the alterations in the gait of OAs with obesity.

Previous studies have shown that beta-band transcranial alternating current stimulation (tACS) applied at the M1 hotspot can modulate corticospinal excitability. However, it remains controversial whether tACS can influence motor unit activities at the spinal cord level. This study aims to compare the efficacy of applying tACS over the hotspot versus the conventional C3 site on motor unit activities and subsequent behavioral changes. This study used a randomized crossover trial design, where fifteen healthy participants performed a paced ball-squeezing exercise while receiving high-definition tACS (HD-tACS) at 21 Hz and 2 mA for 20 min. HD-tACS targeted either the flexor digitorum superficialis (FDS) hotspot or the C3 site, with the order of stimulation randomized for each participant and a 1-week washout period between sessions. Motor unit activities were recorded from the FDS. HD-tACS intervention significantly reduced the variability of motor unit firing rates and increased force variability during isometric force production. The significant modulation effects were seen only when the intervention was applied at the hotspot, but not at the C3 site. Our findings demonstrate that HD-tACS significantly modulates motor unit activities and force variability. The results indicate that cortical-level entrainment by tACS can lead to the modulation of spinal motor neuron activities. Additionally, this study provides further evidence that the C3 site may not be the optimal target for tACS intervention for hand muscles, highlighting the need for personalized neuromodulation strategies.

Objective: This preliminary study investigated whether a single session of high-definition transcranial alternating current stimulation (HD-tACS) could improve corticospinal tract (CST) excitability compared with sham stimulation in healthy individuals and individuals with chronic stroke. Design: Twelve healthy adults and 7 individuals with chronic stroke received active and sham HD-tACS over the primary motor cortex (M1) flexor digitorum superficialis (FDS) hotspot, ipsilesional in stroke subjects, for 30 minutes at 2mA and 21 Hz in a randomized crossover design. All subjects performed robot-assisted grasp-and-open hand exercises during active and sham stimulation. Results: HD-tACS significantly increased FDS MEP amplitudes in the healthy group (15.3%). In the stroke group, FDS MEP amplitudes were increased by ∼22.3% after HD-tACS, but this change was not statistically significant. When MEP amplitudes were normalized as percentage change, HD-tACS significantly increased FDS MEP amplitudes in both groups compared with the sham condition. No significant extensor digitorum communis (EDC) modulation was observed in either group. Conclusion: HD-tACS combined with robot-assisted hand exercises may enhance CST excitability compared with robot-assisted hand exercises alone after a single session in both healthy and stroke subjects. However, larger studies are needed to confirm these findings.

The precise localization of the primary motor cortex (M1) corresponding to specific muscles is critical for enhancing the efficacy of neuromodulation. When navigated transcranial magnetic stimulation (nTMS) or other mapping tools are unavailable, stimulation is typically applied at the C3 site of the standard 10-20 EEG system. However, emerging evidence indicates that C3 may not be the optimal site for targeting hand muscles. Therefore, the goal of this study is to propose an innovative neuroanatomy-based localization method to identify the M1 hotspot for the hand muscle and to validate its effectiveness compared with the C3 site. A step-by-step protocol was developed to identify the M1 hotspot for the flexor digitorum superficialis (FDS) muscle using an acupuncture-based approach. The identified hotspot was then compared with the conventional C3 site by evaluating baseline and post-neuromodulation motor evoked potentials (MEPs). Representative data demonstrated that the proposed M1 hotspot yielded significantly higher MEP amplitudes than the C3 site, both at the baseline and following neuromodulation. The proposed approach provides a validated and practical method for localizing the M1 hotspot for the FDS. This technique has the potential to improve the effectiveness of neuromodulation in clinical practice when advanced neuroimaging tools are not accessible.

Breathing-controlled electrical stimulation (BreEStim) is an innovative neuromodulation intervention that synchronizes deep voluntary breathing with peripheral electrical stimulation. Prior studies have shown its analgesic effects in healthy adults and spinal cord injury patients with neuropathic pain. The present study used EEG to examine BreEStim’s neural effects on sensory, affective, and cognitive components of pain. Fourteen healthy participants (7 M, 7 F) completed 30 min of BreEStim and conventional electrical stimulation (EStim) interventions in a randomized, crossover within-subject design. Electrical pain thresholds (EPT) and EEG were recorded pre- and post-intervention. Event-related potentials (ERPs) at pre-EPT-level stimuli before and immediately after each intervention were analyzed for early sensory (P30) and affective (P250) processing, while resting-state EEG assessed spectral power across delta, theta, alpha, and beta bands for cognitive processing. Both BreEStim and EStim increased EPT, indicating short-term habituation. There was no change in early ERP responses (P30) after each intervention, suggesting preserved sensory perception. BreEStim selectively reduced P250, reflective of the affective component of pain. BreEStim significantly increased delta and theta band power and reduced alpha band power on resting-state EEG analyses, whereas no significant changes after EStim were observed. Collectively, BreEStim preserves sensory encoding while selectively modulating affective and cognitive dimensions of pain, supporting its potential as a targeted, non-pharmacological neuromodulation strategy.