Direct current stimulation of endothelial monolayers induces a transient and reversible increase in transport due to the electroosmotic effect

Transcranial direct current stimulation alters cerebrospinal fluid-interstitial fluid exchange in mouse brain

BACKGROUND

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that has gained prominence recently. Clinical studies have explored tDCS as an adjunct to neurologic disease rehabilitation, with evidence suggesting its potential in modulating brain clearance mechanisms. The glymphatic system, a proposed brain waste clearance system, posits that cerebrospinal fluid-interstitial fluid (CSF-ISF) exchange aids in efficient metabolic waste removal. While some studies have linked tDCS to astrocytic inositol trisphosphate (IP3)/Ca2+ signaling, the impact of tDCS on CSF-ISF exchange dynamics remains unclear.

HYPOTHESIS

tDCS influences the dynamics of CSF-ISF exchange through astrocytic IP3/Ca2+ signaling.

METHODS

In this study, we administered tDCS (0.1 mA for 10 min) to C57BL/6N mice anesthetized with ketamine-xylazine (KX). The anode was positioned on the cranial bone above the cortex, and the cathode was inserted into the neck. Following tDCS, we directly assessed brain fluid dynamics by injecting biotinylated dextran amine (BDA) as a CSF tracer into the cisterna magna (CM). The brain was then extracted after either 30 or 60 min and fixed. After 24 h, the sectioned brain slices were stained with Alexa 594-conjugated streptavidin (SA) to visualize BDA using immunohistochemistry. We conducted Electroencephalography (EEG) recordings and aquaporin 4 (AQP4)/CD31 immunostaining to investigate the underlying mechanisms of tDCS. Additionally, we monitored the efflux of Evans blue, injected into the cisterna magna, using cervical lymph node imaging. Some experiments were subsequently repeated with inositol trisphosphate receptor type 2 (IP3R2) knockout (KO) mice.

RESULTS

Post-tDCS, we observed an increased CSF tracer influx, indicating a modulation of CSF-ISF exchange by tDCS. Additionally, tDCS appeared to enhance the brain's metabolic waste efflux. EEG recordings showed an increase in delta wave post-tDCS. But no significant change in AQP4 expression was detected 30 min post-tDCS. Besides, we found no alteration in CSF-ISF exchange and delta wave activity in IP3R2 KO mice after tDCS.

CONCLUSION

Our findings suggest that tDCS augments the glymphatic system's influx and efflux. Through astrocytic IP3/Ca2+ signaling, tDCS was found to modify the delta wave, which correlates positively with brain clearance. This study underscores the potential of tDCS in modulating brain metabolic waste clearance.

Cytoskeletal Remodeling and Gap Junction Translocation Mediates Blood-Brain Barrier Disruption by Non-invasive Low-Voltage Pulsed Electric Fields

High-voltage pulsed electric fields (HV-PEF) delivered with invasive needle electrodes for electroporation applications is known to induce off-target blood-brain barrier (BBB) disruption. In this study, we sought to determine the feasibility of minimally invasive PEF application to produce BBB disruption in rat brain and identify the putative mechanisms mediating the effect. We observed dose-dependent presence of Evans Blue (EB) dye in rat brain when PEF were delivered with a skull mounted electrode used for neurostimulation application. Maximum region of dye uptake was observed while using 1500 V, 100 pulses, 100 µs and 10 Hz. Results of computational models suggested that the region of BBB disruption was occurring at thresholds of 63 V/cm or higher; well below intensity levels for electroporation. In vitro experiments recapitulating this effect with human umbilical vein endothelial cells (HUVEC) demonstrated cellular alterations that underlie BBB manifests at low-voltage high-pulse conditions without affecting cell viability or proliferation. Morphological changes in HUVECs due to PEF were accompanied by disruption of actin cytoskeleton, loss of tight junction protein-ZO-1 and VE-Cadherin at cell junctions and partial translocation into the cytoplasm. Uptake of propidium iodide (PI) in PEF treated conditions is less than 1% and 2.5% of total number of cells in high voltage (HV) and low-voltage (LV) groups, respectively, implying that BBB disruption to be independent of electroporation under these conditions. 3-D microfabricated blood vessel permeability was found to increase significantly following PEF treatment and confirmed with correlative cytoskeletal changes and loss of tight junction proteins. Finally, we show that the rat brain model can be scaled to human brains with a similar effect on BBB disruption characterized by electric field strength (EFS) threshold and using a combination of two bilateral HD electrode configurations.

The Effects of Transcranial Direct Current Stimulation and Exercise on Salivary S100B Protein Indicated Blood-Brain Barrier Permeability: A Pilot Study

OBJECTIVE

This study aimed to assess the effect of transcranial direct current stimulation (tDCS) and exercise on blood-brain barrier (BBB) permeability in humans as assessed through the quantification of the salivary protein biomarker S100B. It was hypothesized that active tDCS would induce a significant increase in salivary S100B concentration when compared with sham stimulation and no stimulation. It also was hypothesized that the increase in salivary S100B concentration would be greater after active tDCS and exercise than after tDCS or exercise alone.

MATERIALS AND METHODS

A total of 13 healthy adults (five male, eight female), ranging in age from 21 to 32 years, underwent three experimental conditions (active tDCS, sham tDCS, inactive control). To assess exercise- and tDCS-induced changes in BBB permeability, S100B in saliva was measured. Saliva samples were taken before tDCS, after tDCS, and immediately after a ramped cycling time-to-exhaustion (TTE) task. Active tDCS involved the application of anodal stimulation over the primary motor cortex for 20 minutes at 2 mA.

RESULTS

S100B concentrations in the control condition did not differ significantly from the active condition (estimate = 0.10, SE = 0.36, t = 0.27, p = 0.79) or the sham condition (estimate = 0.33, SE = 0.36, t = 0.89, p = 0.38). Similarly, S100B concentrations at baseline did not differ significantly from post-intervention (estimate = -0.35, SE = 0.34, t = -1.03, p = 0.31) or post-TTE (estimate = 0.66, SE = 0.34, t = 1.93, p = 0.06).

CONCLUSIONS

This research provides novel insight into the effect of tDCS and exercise on S100B-indicated BBB permeability in humans. Although the effects of tDCS were not significant, increases in salivary S100B after a fatiguing cycling task may indicate exercise-induced changes in BBB permeability.

Less might be more: 1 mA but not 1.5 mA of tDCS improves tactile orientation discrimination

Background

Transcranial direct current stimulation (tDCS) is a frequently used brain stimulation method; however, studies on tactile perception using tDCS are inconsistent, which might be explained by the variations in endogenous and exogenous parameters that influence tDCS.

Objectives

We aimed to investigate the effect of one of these endogenous parameters-the tDCS amplitude-on tactile perception.

Methods

We conducted this experiment on 28 undergraduates/graduates aged 18-36 years. In separate sessions, participants received 20 min of 1 mA or 1.5 mA current tDCS in a counterbalanced order. Half of the participants received anodal tDCS of the left SI coupled with cathodal tDCS of the right SI, and this montage was reversed for the other half. Pre- and post-tDCS tactile discrimination performance was assessed using the Grating Orientation Task (GOT). In this task, plastic domes with gratings of different widths cut into their surfaces are placed on the fingertip, and participants have to rate the orientation of the gratings.

Results

Linear modeling with amplitude, dome, and session as within factors and montage as between factors revealed the following: significant main effects of grating width, montage, and session and a marginally significant interaction effect of session and amplitude. Posthoc t-tests indicated that performance in GOT improved after 1 mA but not 1.5 mA tDCS independent of the montage pattern of the electrodes.

Conclusion

Increasing the stimulation amplitude from 1 mA to 1.5 mA does not facilitate the tDCS effect on GOT performance. On the contrary, the effect seemed more robust for the lower-current amplitude.

Breaking barriers: exploring mechanisms behind opening the blood-brain barrier

The blood-brain barrier (BBB) is a selectively permeable membrane that separates the bloodstream from the brain. While useful for protecting neural tissue from harmful substances, brain-related diseases are difficult to treat due to this barrier, as it also limits the efficacy of drug delivery. To address this, promising new approaches for enhancing drug delivery are based on disrupting the BBB using physical means, including optical/photothermal therapy, electrical stimulation, and acoustic/mechanical stimulation. These physical mechanisms can temporarily and locally open the BBB, allowing drugs and other substances to enter. Focused ultrasound is particularly promising, with the ability to focus energies to targeted, deep-brain regions. In this review, we examine recent advances in physical approaches for temporary BBB disruption, describing their underlying mechanisms as well as evaluating the utility of these physical approaches with regard to their potential risks and limitations. While these methods have demonstrated efficacy in disrupting the BBB, their safety, comparative efficacy, and practicality for clinical use remain an ongoing topic of research.

Multi-scale multi-physics model of brain interstitial water flux by transcranial Direct Current Stimulation

Objective. Transcranial direct current stimulation (tDCS) generates sustained electric fields in the brain, that may be amplified when crossing capillary walls (across blood-brain barrier, BBB). Electric fields across the BBB may generate fluid flow by electroosmosis. We consider that tDCS may thus enhance interstitial fluid flow.Approach. We developed a modeling pipeline novel in both (1) spanning the mm (head),μm (capillary network), and then nm (down to BBB tight junction (TJ)) scales; and (2) coupling electric current flow to fluid current flow across these scales. Electroosmotic coupling was parametrized based on prior measures of fluid flow across isolated BBB layers. Electric field amplification across the BBB in a realistic capillary network was converted to volumetric fluid exchange.Main results. The ultrastructure of the BBB results in peak electric fields (per mA of applied current) of 32-63Vm-1across capillary wall and >1150Vm-1in TJs (contrasted with 0.3Vm-1in parenchyma). Based on an electroosmotic coupling of 1.0 × 10-9- 5.6 × 10-10m3s-1m2perVm-1, peak water fluxes across the BBB are 2.44 × 10-10- 6.94 × 10-10m3s-1m2, with a peak 1.5 × 10-4- 5.6 × 10-4m3min-1m3interstitial water exchange (per mA).Significance. Using this pipeline, the fluid exchange rate per each brain voxel can be predicted for any tDCS dose (electrode montage, current) or anatomy. Under experimentally constrained tissue properties, we predicted tDCS produces a fluid exchange rate comparable to endogenous flow, so doubling fluid exchange with further local flow rate hot spots ('jets'). The validation and implication of such tDCS brain 'flushing' is important to establish.

Is blood-brain barrier a probable mediator of non-invasive brain stimulation effects on Alzheimer's disease?

Alzheimer's disease (AD) is a complex neurodegenerative disease with no existing treatment leading to full recovery. The blood-brain barrier (BBB) breakdown usually precedes the advent of first symptoms in AD and accompanies the progression of the disease. At the same time deliberate BBB opening may be beneficial for drug delivery in AD. Non-invasive brain stimulation (NIBS) techniques, primarily transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), have shown multiple evidence of being able to alleviate symptoms of AD. Currently, TMS/tDCS mechanisms are mostly investigated in terms of their neuronal effects, while their possible non-neuronal effects, including mitigation of the BBB disruption, are less studied. We argue that studies of TMS/tDCS effects on the BBB in AD are necessary to boost the effectiveness of neuromodulation in AD. Moreover, such studies are important considering the safety issues of TMS/tDCS use in the advanced AD stages when the BBB is usually dramatically deteriorated. Here, we elucidate the evidence of NIBS-induced BBB opening and closing in various models from in vitro to humans, and highlight its importance in AD.

Transcranial direct current stimulation for bipolar depression: systematic reviews of clinical evidence and biological underpinnings

Despite multiple available treatments for bipolar depression (BD), many patients face sub-optimal responses. Transcranial direct current stimulation (tDCS) has been advocated in the management of different conditions, including BD, especially in treatment-resistant cases. The optimal dose and timing of tDCS, the mutual influence with other concurrently administered interventions, long-term efficacy, overall safety, and biological underpinnings nonetheless deserve additional assessment. The present study appraised the existing clinical evidence about tDCS for bipolar depression, delving into the putative biological underpinnings with a special emphasis on cellular and molecular levels, with the ultimate goal of providing a translational perspective on the matter. Two separate systematic reviews across the PubMed database since inception up to August 8^th 2022 were performed, with fourteen clinical and nineteen neurobiological eligible studies. The included clinical studies encompass 207 bipolar depression patients overall and consistently document the efficacy of tDCS, with a reduction in depression scores after treatment ranging from 18% to 92%. The RCT with the largest sample clearly showed a significant superiority of active stimulation over sham. Mild-to-moderate and transient adverse effects are attributed to tDCS across these studies. The review of neurobiological literature indicates that several molecular mechanisms may account for the antidepressant effect of tDCS in BD patients, including the action on calcium homeostasis in glial cells, the enhancement of LTP, the regulation of neurotrophic factors and inflammatory mediators, and the modulation of the expression of plasticity-related genes. To the best of our knowledge, this is the first study on the matter to concurrently provide a synthesis of the clinical evidence and an in-depth appraisal of the putative biological underpinnings, providing consistent support for the efficacy, safety, and tolerability of tDCS.

Direct current stimulation increases blood flow and permeability of cortical microvasculature in vivo

BACKGROUND AND PURPOSE

Transcranial direct current stimulation (DCS) structurally and functionally modulates neuronal networks and microglia dynamics. Neurovascular coupling adapts regional cerebral blood flow to neuronal activity and metabolic demands.

METHODS

In this study, we examined effects of anodal DCS on vessel morphology, blood flow parameters, permeability of cortical microvasculature, and perivascular microglia motility by time-lapse two-photon microscopy in anaesthetized mice.

RESULTS

Low-intensity DCS significantly increased vessel diameter and blood flow parameters. These effects were transient and dependent on the spontaneous vasomotion characteristics of the individual vessel. Vessel leakage increased significantly after DCS at 1.1 and was more pronounced at 2.2 A/m² , indicating a dose-dependent increase in vascular permeability. Perivascular microglia exhibited increased soma motility post-DCS at both intensities, potentially triggered by the extravasation of intravascular substrates.

CONCLUSIONS

Our findings demonstrate that DCS affected only vessels with spontaneous vasomotion. This rapid vascular response may occur as an adaptation of regional blood supply to neuronal excitability altered by DCS or as a direct effect on the vessel wall. In contrast to these immediate effects during stimulation, increases in cortical vessel permeability and perivascular microglia motility appeared after the stimulation had ended.

Neurocapillary-Modulation

OBJECTIVES

We consider two consequences of brain capillary ultrastructure in neuromodulation. First, blood-brain barrier (BBB) polarization as a consequence of current crossing between interstitial space and the blood. Second, interstitial current flow distortion around capillaries impacting neuronal stimulation.

MATERIALS AND METHODS

We developed computational models of BBB ultrastructure morphologies to first assess electric field amplification at the BBB (principle 1) and neuron polarization amplification by the presence of capillaries (principle 2). We adapt neuron cable theory to develop an analytical solution for maximum BBB polarization sensitivity.

RESULTS

Electrical current crosses between the brain parenchyma (interstitial space) and capillaries, producing BBB electric fields (EBBB) that are >400x of the average parenchyma electric field (ĒBRAIN), which in turn modulates transport across the BBB. Specifically, for a BBB space constant (λBBB) and wall thickness (dth-BBB), the analytical solution for maximal BBB electric field (EABBB) is given as: (ĒBRAIN × λBBB)/dth-BBB. Electrical current in the brain parenchyma is distorted around brain capillaries, amplifying neuronal polarization. Specifically, capillary ultrastructure produces ∼50% modulation of the ĒBRAIN over the ∼40 μm inter-capillary distance. The divergence of EBRAIN (Activating function) is thus ∼100 kV/m2 per unit ĒBRAIN.

CONCLUSIONS

BBB stimulation by principle 1 suggests novel therapeutic strategies such as boosting metabolic capacity or interstitial fluid clearance. Whereas the spatial profile of EBRAIN is traditionally assumed to depend only on macroscopic anatomy, principle 2 suggests a central role for local capillary ultrastructure-which impact forms of neuromodulation including deep brain stimulation (DBS), spinal cord stimulation (SCS), transcranial magnetic stimulation (TMS), electroconvulsive therapy (ECT), and transcranial electrical stimulation (tES)/transcranial direct current stimulation (tDCS).

Neuroprotection and Non-Invasive Brain Stimulation: Facts or Fiction?

Non-Invasive Brain Stimulation (NIBS) techniques, such as transcranial Direct Current Stimulation (tDCS) and repetitive Magnetic Transcranial Stimulation (rTMS), are well-known non-pharmacological approaches to improve both motor and non-motor symptoms in patients with neurodegenerative disorders. Their use is of particular interest especially for the treatment of cognitive impairment in Alzheimer's Disease (AD), as well as axial disturbances in Parkinson's (PD), where conventional pharmacological therapies show very mild and short-lasting effects. However, their ability to interfere with disease progression over time is not well understood; recent evidence suggests that NIBS may have a neuroprotective effect, thus slowing disease progression and modulating the aggregation state of pathological proteins. In this narrative review, we gather current knowledge about neuroprotection and NIBS in neurodegenerative diseases (i.e., PD and AD), just mentioning the few results related to stroke. As further matter of debate, we discuss similarities and differences with Deep Brain Stimulation (DBS)-induced neuroprotective effects, and highlight possible future directions for ongoing clinical studies.

Direct current stimulation modulates gene expression in isolated astrocytes with implications for glia-mediated plasticity

While the applications of transcranial direct current stimulation (tDCS) across brain disease and cognition are diverse, they rely on changes in brain function outlasting stimulation. The cellular mechanisms of DCS leading to brain plasticity have been studied, but the role of astrocytes remains unaddressed. We previously predicted that during tDCS current is concentrated across the blood brain-barrier. This will amplify exposure of endothelial cells (ECs) that form blood vessels and of astrocytes that wrap around them. The objective of this study was to investigate the effect of tDCS on the gene expression by astrocytes or ECs. DCS (0.1 or 1 mA, 10 min) was applied to monolayers of mouse brain ECs or human astrocytes. Gene expression of a set of neuroactive genes were measured using RT-qPCR. Expression was assessed immediately or 1 h after DCS. Because we previously showed that DCS can produce electroosmotic flow and fluid shear stress known to influence EC and astrocyte function, we compared three interventions: pressure-driven flow across the monolayer alone, pressure-driven flow plus DCS, and DCS alone with flow blocked. We show that DCS can directly modulate gene expression in astrocytes (notably FOS and BDNF), independent of but synergistic with pressure-driven flow gene expression. In ECs, pressure-driven flow activates genes expression with no evidence of further contribution from DCS. In ECs, DCS alone produced mixed effects including an upregulation of FGF9 and downregulation of NTF3. We propose a new adjunct mechanism for tDCS based on glial meditated plasticity.

Electric Fields Induced in the Brain by Transcranial Electric Stimulation: A Review of In Vivo Recordings

Transcranial electrical stimulation (tES) techniques, such as direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS), cause neurophysiological and behavioral modifications as responses to the electric field are induced in the brain. Estimations of such electric fields are based mainly on computational studies, and in vivo measurements have been used to expand the current knowledge. Here, we review the current tDCS- and tACS-induced electric fields estimations as they are recorded in humans and non-human primates using intracerebral electrodes. Direct currents and alternating currents were applied with heterogeneous protocols, and the recording procedures were characterized by a tentative methodology. However, for the clinical stimulation protocols, an injected current seems to reach the brain, even at deep structures. The stimulation parameters (e.g., intensity, frequency and phase), the electrodes’ positions and personal anatomy determine whether the intensities might be high enough to affect both neuronal and non-neuronal cell activity, also deep brain structures.

Effects of central nervous system electrical stimulation on non-neuronal cells

Over the past few decades, much progress has been made in the clinical use of electrical stimulation of the central nervous system (CNS) to treat an ever-growing number of conditions from Parkinson's disease (PD) to epilepsy as well as for sensory restoration and many other applications. However, little is known about the effects of microstimulation at the cellular level. Most of the existing research focuses on the effects of electrical stimulation on neurons. Other cells of the CNS such as microglia, astrocytes, oligodendrocytes, and vascular endothelial cells have been understudied in terms of their response to stimulation. The varied and critical functions of these cell types are now beginning to be better understood, and their vital roles in brain function in both health and disease are becoming better appreciated. To shed light on the importance of the way electrical stimulation as distinct from device implantation impacts non-neuronal cell types, this review will first summarize common stimulation modalities from the perspective of device design and stimulation parameters and how these different parameters have an impact on the physiological response. Following this, what is known about the responses of different cell types to different stimulation modalities will be summarized, drawing on findings from both clinical studies as well as clinically relevant animal models and in vitro systems.

Human dermal microvascular endothelial cell morphological response to fluid shear stress

As the cells that line the vasculature, endothelial cells are continually exposed to fluid shear stress by blood flow. Recent studies suggest that the morphological response of endothelial cells to fluid shear stress depends on the endothelial cell type. Thus, the present study characterizes the morphological response of human dermal microvascular endothelial cells (HMEC-1) and nuclei to steady, laminar, and unidirectional fluid shear stress. Cultured HMEC-1 monolayers were exposed to shear stress of 0.3 dyn/cm², 16 dyn/cm², or 32 dyn/cm² for 72 h with hourly live-cell imaging capturing both the nuclear and cellular morphology. Despite changes in elongation and alignment occurring with increasing fluid shear stress, there was a lack of elongation and alignment over time under each fluid shear stress condition. Conversely, changes in cellular and nuclear area exhibited dependence on both time and fluid shear stress magnitude. The trends in cellular morphology differed at shear stress levels above and below 16 dyn/cm², whereas the nuclear orientation was independent of fluid shear stress magnitude. These findings show the complex morphological response of HMEC-1 to fluid shear stress.

Transcranial Direct Current Stimulation Alleviates Neurovascular Unit Dysfunction in Mice With Preclinical Alzheimer’s Disease

Neurons, glial cells and blood vessels are collectively referred to as the neurovascular unit (NVU). In the Alzheimer’s disease (AD) brain, the main components of the NVU undergo pathological changes. Transcranial direct current stimulation (tDCS) can protect neurons, induce changes in glial cells, regulate cerebral blood flow, and exert long-term neuroprotection. However, the mechanism by which tDCS improves NVU function is unclear. In this study, we explored the effect of tDCS on the NVU in mice with preclinical AD and the related mechanisms. 10 sessions of tDCS were given to six-month-old male APP/PS1 mice in the preclinical stage. The model group, sham stimulation group, and control group were made up of APP/PS1 mice and C57 mice of the same age. All mice were histologically evaluated two months after receiving tDCS. Protein content was measured using Western blotting and an enzyme-linked immunosorbent assay (ELISA). The link between glial cells and blood vessels was studied using immunofluorescence staining and lectin staining. The results showed that tDCS affected the metabolism of Aβ; the levels of Aβ, amyloid precursor protein (APP) and BACE1 were significantly reduced, and the levels of ADAM10 were significantly increased in the frontal cortex and hippocampus in the stimulation group. In the stimulation group, tDCS reduced the protein levels of Iba1 and GFAP and increased the protein levels of NeuN, LRP1 and PDGRFβ. This suggests that tDCS can improve NVU function in APP/PS1 mice in the preclinical stage. Increased blood vessel density and blood vessel length, decreased IgG extravasation, and increased the protein levels of occludin and coverage of astrocyte foot processes with blood vessels suggested that tDCS had a protective effect on the blood-brain barrier. Furthermore, the increased numbers of Vimentin, S100 expression and blood vessels (lectin-positive) around Aβ indicated that the effect of tDCS was mediated by astrocytes and blood vessels. There was no significant difference in these parameters between the model group and the sham stimulation group. In conclusion, our results show that tDCS can improve NVU function in APP/PS1 mice in the preclinical stage, providing further support for the use of tDCS as a treatment for AD.

Experience-dependent associations between distinct subtypes of childhood trauma and brain function and architecture

Background

Childhood trauma can alter brain-development trajectories and lead to a greater risk of psychopathology developing in adulthood. For this reason, understanding experience-dependent brain abnormalities associated with different trauma subtypes is crucial for identifying developmental processes disrupted by unfavorable early environments and for proposing early intervention measures to reduce trauma's negative effects.

Methods

This study used multimodal magnetic resonance imaging (MRI) to explore the neural correlates of distinct subtypes of childhood trauma. We recruited a large community sample of young adults (mean age, 24.1, SD 1.9 years) who completed a Childhood Trauma Questionnaire, were given behavioral scores, and underwent multimodal MRI. To quantify brain changes, we used functional connectivity density (FCD) mapping based on whole brain analysis, regions of interest (ROI) analysis, and morphological measurements. Experience-dependent brain abnormalities were identified by multivariable linear regression.

Results

We found that diverse brain regions in the FCD mapping were significantly related to 4 trauma subtypes and belonged to different cognitive components used for various behaviors. Experience-related influences on functional circuits and brain morphology were observed in extensive regions, including the sensorimotor, cingulum, accumbens, insula, and frontal-parietal areas, as well as in regions within the default mode network.

Conclusions

Identifying specific regions or systems may be a valid strategy for understanding the pathogenesis and development process of psychiatric disorders in people with different traumatic experiences and may facilitate better-targeted intervention strategies for maltreated children.

Dataset of concurrent EEG, ECG, and behavior with multiple doses of transcranial electrical stimulation

We present a dataset combining human-participant high-density electroencephalography (EEG) with physiological and continuous behavioral metrics during transcranial electrical stimulation (tES). Data include within participant application of nine High-Definition tES (HD-tES) types, targeting three cortical regions (frontal, motor, parietal) with three stimulation waveforms (DC, 5 Hz, 30 Hz); more than 783 total stimulation trials over 62 sessions with EEG, physiological (ECG, EOG), and continuous behavioral vigilance/alertness metrics. Experiment 1 and 2 consisted of participants performing a continuous vigilance/alertness task over three 70-minute and two 70.5-minute sessions, respectively. Demographic data were collected, as well as self-reported wellness questionnaires before and after each session. Participants received all 9 stimulation types in Experiment 1, with each session including three stimulation types, with 4 trials per type. Participants received two stimulation types in Experiment 2, with 20 trials of a given stimulation type per session. Within-participant reliability was tested by repeating select sessions. This unique dataset supports a range of hypothesis testing including interactions of tDCS/tACS location and frequency, brain-state, physiology, fatigue, and cognitive performance.

Direct Current Stimulation Disrupts Endothelial Glycocalyx and Tight Junctions of the Blood-Brain Barrier in vitro

Transcranial direct current stimulation (tDCS) is a non-invasive physical therapy to treat many psychiatric disorders and to enhance memory and cognition in healthy individuals. Our recent studies showed that tDCS with the proper dosage and duration can transiently enhance the permeability (P) of the blood-brain barrier (BBB) in rat brain to various sized solutes. Based on the in vivo permeability data, a transport model for the paracellular pathway of the BBB also predicted that tDCS can transiently disrupt the endothelial glycocalyx (EG) and the tight junction between endothelial cells. To confirm these predictions and to investigate the structural mechanisms by which tDCS modulates P of the BBB, we directly quantified the EG and tight junctions of in vitro BBB models after DCS treatment. Human cerebral microvascular endothelial cells (hCMECs) and mouse brain microvascular endothelial cells (bEnd3) were cultured on the Transwell filter with 3 μm pores to generate in vitro BBBs. After confluence, 0.1–1 mA/cm² DCS was applied for 5 and 10 min. TEER and P to dextran-70k of the in vitro BBB were measured, HS (heparan sulfate) and hyaluronic acid (HA) of EG was immuno-stained and quantified, as well as the tight junction ZO-1. We found disrupted EG and ZO-1 when P to dextran-70k was increased and TEER was decreased by the DCS. To further investigate the cellular signaling mechanism of DCS on the BBB permeability, we pretreated the in vitro BBB with a nitric oxide synthase (NOS) inhibitor, L-NMMA. L-NMMA diminished the effect of DCS on the BBB permeability by protecting the EG and reinforcing tight junctions. These in vitro results conform to the in vivo observations and confirm the model prediction that DCS can disrupt the EG and tight junction of the BBB. Nevertheless, the in vivo effects of DCS are transient which backup its safety in the clinical application. In conclusion, our current study directly elucidates the structural and signaling mechanisms by which DCS modulates the BBB permeability.

Influence of Anisotropic White Matter on Electroosmotic Flow Induced by Direct Current

Treatment of cerebral edema remains a major challenge in clinical practice and new innovative therapies are needed. This study presents a novel approach for mitigating cerebral edema by inducing bulk fluid transport utilizing the brain’s electroosmotic property using an anatomically detailed finite element head model incorporating anisotropy in the white matter (WM). Three representative anisotropic conductivity algorithms are employed for the WM and compared with isotropic WM. The key results are (1) the electroosmotic flow (EOF) is driven from the edema region to the subarachnoid space under an applied electric field with its magnitude linearly correlated to the electric field and direction following current flow pathways; (2) the extent of EOF distribution variation correlates highly with the degree of the anisotropic ratio of the WM regions; (3) the directions of the induced EOF in the anisotropic models deviate from its isotropically defined pathways and tend to move along the principal fiber direction. The results suggest WM anisotropy should be incorporated in head models for more reliable EOF evaluations for cerebral edema mitigation and demonstrate the promise of the electroosmosis based approach to be developed as a new therapy for edema treatment as evaluated with enhanced head models incorporating WM anisotropy.

Electroosmosis Based Novel Treatment Approach for Cerebral Edema

OBJECTIVE

Cerebral edema characterized as an abnormal accumulation of interstitial fluid has not been treated effectively. We propose a novel edema treatment approach to drive edematous fluid out of the brain by direct current utilizing brain tissue's electroosmotic property.

METHODS

A finite element (FE) head model is developed and employed to assess the feasibility of the approach. First, the capacity of the model for electric field prediction is validated against human experiments. Second, two electrode configurations (S and D-montage) are designed to evaluate the distribution of the electric field, electroosmotic flow (EOF), current density, and temperature across the brain under an applied direct current.

RESULTS

The S-montage is shown to induce an average EOF velocity of 7e-4 mm/s underneath the anode by a voltage of 15 V, and the D-montage induces a velocity of 9e-4 mm/s by a voltage of 5 V. Meanwhile, the brain temperature in both configurations is below 38 °C, which is within the safety range. Further, the magnitude of EOF is proportional to the electric field, and the EOF direction follows the current flow from anode to cathode. The EOF velocity in the white matter is significantly higher than that in the gray matter under the anode where the fluid is to be drawn out.

CONCLUSION

The proposed electroosmosis based approach allows alleviating brain edema within the critical time window by direct current.

SIGNIFICANCE

The approach may be further developed as a new treatment solely or as a complement to existing conventional treatments of edema.

Personalised, image-guided, noninvasive brain stimulation in gliomas: Rationale, challenges and opportunities

Malignant brain tumours are among the most aggressive human cancers, and despite intensive efforts made over the last decades, patients’ survival has scarcely improved. Recently, high-grade gliomas (HGG) have been found to be electrically integrated with healthy brain tissue, a communication that facilitates tumour mitosis and invasion. This link to neuronal activity has provided new insights into HGG pathophysiology and opened prospects for therapeutic interventions based on electrical modulation of neural and synaptic activity in the proximity of tumour cells, which could potentially slow tumour growth. Noninvasive brain stimulation (NiBS), a group of techniques used in research and clinical settings to safely modulate brain activity and plasticity via electromagnetic or electrical stimulation, represents an appealing class of interventions to characterise and target the electrical properties of tumour-neuron interactions. Beyond neuronal activity, NiBS may also modulate function of a range of substrates and dynamics that locally interacts with HGG (e.g., vascular architecture, perfusion and blood-brain barrier permeability). Here we discuss emerging applications of NiBS in patients with brain tumours, covering potential mechanisms of action at both cellular, regional, network and whole-brain levels, also offering a conceptual roadmap for future research to prolong survival or promote wellbeing via personalised NiBS interventions.

Neurovascular-modulation: A review of primary vascular responses to transcranial electrical stimulation as a mechanism of action

BACKGROUND

The ubiquitous vascular response to transcranial electrical stimulation (tES) has been attributed to the secondary effect of neuronal activity forming the classic neurovascular coupling. However, the current density delivered transcranially concentrates in: A) the cerebrospinal fluid of subarachnoid space where cerebral vasculature resides after reaching the dural and pial surfaces and B) across the blood-brain-barrier after reaching the brain parenchyma. Therefore, it is anticipated that tES has a primary vascular influence.

OBJECTIVES

Focused review of studies that demonstrated the direct vascular response to electrical stimulation and studies demonstrating evidence for tES-induced vascular effect in coupled neurovascular systems.

RESULTS

tES induces both primary and secondary vascular phenomena originating from four cellular elements; the first two mediating a primary vascular phenomenon mainly in the form of an immediate vasodilatory response and the latter two leading to secondary vascular effects and as parts of classic neurovascular coupling: 1) The perivascular nerves of more superficially located dural and pial arteries and medium-sized arterioles with multilayered smooth muscle cells; and 2) The endothelial lining of all vessels including microvasculature of blood-brain barrier; 3) Astrocytes; and 4) Neurons of neurovascular units.

CONCLUSION

A primary vascular effect of tES is highly suggested based on various preclinical and clinical studies. We explain how the nature of vascular response can depend on vessel anatomy (size) and physiology and be controlled by stimulation waveform. Further studies are warranted to investigate the mechanisms underlying the vascular response and its contribution to neural activity in both healthy brain and pathological conditions - recognizing many brain diseases are associated with alteration of cerebral hemodynamics and decoupling of neurovascular units.

fMRI and transcranial electrical stimulation (tES): A systematic review of parameter space and outcomes

The combination of non-invasive brain stimulation interventions with human brain mapping methods have supported research beyond correlational associations between brain activity and behavior. Functional MRI (fMRI) partnered with transcranial electrical stimulation (tES) methods, i.e., transcranial direct current (tDCS), transcranial alternating current (tACS), and transcranial random noise (tRNS) stimulation, explore the neuromodulatory effects of tES in the targeted brain regions and their interconnected networks and provide opportunities for individualized interventions. Advances in the field of tES-fMRI can be hampered by the methodological variability between studies that confounds comparability/replicability. In order to explore variability in the tES-fMRI methodological parameter space (MPS), we conducted a systematic review of 222 tES-fMRI experiments (181 tDCS, 39 tACS and 2 tRNS) published before February 1, 2019, and suggested a framework to systematically report main elements of MPS across studies. Publications dedicated to tRNS-fMRI were not considered in this systematic review. We have organized main findings in terms of fMRI modulation by tES. tES modulates activation and connectivity beyond the stimulated areas particularly with prefrontal stimulation. There were no two studies with the same MPS to replicate findings. We discuss how to harmonize the MPS to promote replication in future studies.

Direct current electric field regulates endothelial permeability under physiologically relevant fluid forces in a microfluidic vessel bifurcation model

Previous in vitro studies have reported on the use of direct current electric fields (DC-EFs) to regulate vascular endothelial permeability, which is important for tissue regeneration and wound healing. However, these studies have primarily used static 2D culture models that lack the fluid mechanical forces associated with blood flow experienced by endothelial cells (ECs) in vivo. Hence, the effect of DC-EF on ECs under physiologically relevant fluid forces is yet to be systematically evaluated. Using a 3D microfluidic model of a bifurcating vessel, we report the role of DC-EF on regulating endothelial permeability when co-applied with physiologically relevant fluid forces that arise at the vessel bifurcation. The application of a 70 V m-1 DC-EF simultaneously with 1 μL min-1 low perfusion rate (generating 3.8 dyn cm-2 stagnation pressure at the bifurcation point and 0.3 dyn cm-2 laminar shear stress in the branched vessel) increased the endothelial permeability 7-fold compared to the static control condition (i.e., without flow and DC-EF). When the perfusion rate was increased to 10 μL min-1 (generating 38 dyn cm-2 stagnation pressure at the bifurcation point and 3 dyn cm-2 laminar shear stress in the branched vessel) while maintaining the same electrical stimulation, a 4-fold increase in endothelial permeability compared to the static control was observed. The lower increase in endothelial permeability for the higher fluid forces but the same DC-EF suggests a competing role between fluid forces and the applied DC-EF. Moreover, the observed increase in endothelial permeability due to combined DC-EF and flow was transient and dependent on the Akt signalling pathway. Collectively, these findings provide significant new insights into how the endothelium serves as an electro-mechanical interface for regulating vessel permeability.

Group and individual level variations between symmetric and asymmetric DLPFC montages for tDCS over large scale brain network nodes

Two challenges to optimizing transcranial direct current stimulation (tDCS) are selecting between, often similar, electrode montages and accounting for inter-individual differences in response. These two factors are related by how tDCS montage determines current flow through the brain considered across or within individuals. MRI-based computational head models (CHMs) predict how brain anatomy determines electric field (EF) patterns for a given tDCS montage. Because conventional tDCS produces diffuse brain current flow, stimulation outcomes may be understood as modulation of global networks. Therefore, we developed a network-led, rather than region-led, approach. We specifically considered two common "frontal" tDCS montages that nominally target the dorsolateral prefrontal cortex; asymmetric "unilateral" (anode/cathode: F4/Fp1) and symmetric "bilateral" (F4/F3) electrode montages. CHMs of 66 participants were constructed. We showed that cathode location significantly affects EFs in the limbic network. Furthermore, using a finer parcellation of large-scale networks, we found significant differences in some of the main nodes within a network, even if there is no difference at the network level. This study generally demonstrates a methodology for considering the components of large-scale networks in CHMs instead of targeting a single region and specifically provides insight into how symmetric vs asymmetric frontal tDCS may differentially modulate networks across a population.

Designing electrode configuration of electroosmosis based edema treatment as a complement to hyperosmotic therapy

BACKGROUND

Hyperosmotic therapy is a mainstay treatment for cerebral edema. Although often effective, its disadvantages include mainly acting on the normal brain region with limited effectiveness in eliminating excess fluid in the edema region. This study investigates how to configure our previously proposed novel electroosmosis based edema treatment as a complement to hyperosmotic therapy.

METHODS

Three electrode configurations are designed to drive the excess fluid out of the edema region, including 2-electrode, 3-electrode, and 5-electrode designs. The focality and directionality of the induced electroosmotic flow (EOF) are then investigated using the same patient-specific head model with localized edema.

RESULTS

The 5-electrode design shows improved EOF focality with reduced effect on the normal brain region than the other two designs. Importantly, this design also achieves better directionality driving excess edema tissue fluid to a larger region of surrounding normal brain where hyperosmotic therapy functions better. Thus, the 5-electrode design is suggested to treat edema more efficiently via a synergic effect: the excess fluid is first driven out from the edema to surrounding normal brain via EOF, where it can then be treated with hyperosmotic therapy. Meanwhile, the 5-electrode design drives 2.22 mL excess fluid from the edema region in an hour comparable to the other designs, indicating a similar efficiency of EOF.

CONCLUSIONS

The results show that the promise of our previously proposed novel electroosmosis based edema treatment can be designed to achieve better focality and directionality towards a complement to hyperosmotic therapy.

Limited Sensitivity of Hippocampal Synaptic Function or Network Oscillations to Unmodulated Kilohertz Electric Fields

Understanding the cellular mechanisms of kilohertz (kHz) electrical stimulation is of broad interest in neuromodulation including forms of transcranial electrical stimulation, interferential stimulation, and high-rate spinal cord stimulation (SCS). Yet, the well-established low-pass filtering by neuronal membranes suggests minimal neuronal polarization in respond to charge-balanced kHz stimulation. The hippocampal brain slice model is among the most studied systems in neuroscience and exhaustively characterized in screening the effects of electrical stimulation. High-frequency electric fields of varied amplitudes (1–150 V/m), waveforms (sinusoidal, symmetrical pule, asymmetrical pulse) and frequencies (1 and10 kHz) were tested. Changes in single or paired-pulse field EPSPs (fEPSP) in CA1 were measured in response to radial-directed and tangential-directed electric fields, with brief (30 s) or long (30 min) application times. The effects of kHz stimulation on ongoing endogenous network activity were tested in carbachol-induced γ oscillation of CA3a and CA3c. Across 23 conditions evaluated, no significant changes in fEPSP were resolved, while responses were detected for within-slice control direct current (DC) fields; 1-kHz sinusoidal and pulse stimulation (≥60 V/m), but not 10 kHz, induced changes in oscillating neuronal network. We thus report no responses to low-amplitude 1-kHz or any 10-kHz fields, suggesting that any brain sensitivity to these fields is via yet to be-determined mechanism(s) of action which were not identified in our experimental preparation.

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.

Temporal interference stimulation targets deep brain regions by modulating neural oscillations

BACKGROUND

Temporal interference (TI) stimulation of the brain generates amplitude-modulated electric fields oscillating in the kHz range with the goal of non-invasive targeted deep brain stimulation. Yet, the current intensities required in human (sensitivity) to modulate deep brain activity and if superficial brain region are spared (selectivity) at these intensities remains unclear.

OBJECTIVE

We developed an experimentally constrained theory for TI sensitivity to kHz electric field given the attenuation by membrane low-pass filtering property, and for TI selectivity to deep structures given the distribution of modulated and unmodulated electric fields in brain.

METHODS

The electric field threshold to modulate carbachol-induced gamma oscillations in rat hippocampal slices was determined for unmodulated 0.05-2 kHz sine waveforms, and 5 Hz amplitude-modulated waveforms with 0.1-2 kHz carrier frequencies. The neuronal effects are replicated with a computational network model to explore the underlying mechanisms, and then coupled to a validated current-flow model of the human head.

RESULTS

Amplitude-modulated electric fields are stronger in deep brain regions, while unmodulated electric fields are maximal at the cortical regions. Both experiment and model confirmed the hypothesis that spatial selectivity of temporal interference stimulation depends on the phasic modulation of neural oscillations only in deep brain regions. Adaptation mechanism (e.g. GABA_b) enhanced sensitivity to amplitude modulated waveform in contrast to unmodulated kHz and produced selectivity in modulating gamma oscillation (i.e. Higher gamma modulation in amplitude modulated vs unmodulated kHz stimulation). Selection of carrier frequency strongly affected sensitivity to amplitude modulation stimulation. Amplitude modulated stimulation with 100 Hz carrier frequency required ∼5 V/m (corresponding to ∼13 mA at the scalp surface), whereas, 1 kHz carrier frequency ∼60 V/m (∼160 mA) and 2 kHz carrier frequency ∼80 V/m (∼220 mA) to significantly modulate gamma oscillation. Sensitivity is increased (scalp current required decreased) for theoretical neuronal membranes with faster time constants.

CONCLUSION

The TI sensitivity (current required at the scalp) depends on the neuronal membrane time-constant (e.g. axons) approaching the kHz carrier frequency. TI selectivity is governed by network adaption (e.g. GABA_b) that is faster than the amplitude-modulation frequency. Thus, we show neuronal and network oscillations time-constants determine the scalp current required and the selectivity achievable with TI in humans.

Modulation of solute diffusivity in brain tissue as a novel mechanism of transcranial direct current stimulation (tDCS)

The breadth of brain disorders and functions reported responsive to transcranial direct current stimulation (tDCS) suggests a generalizable mechanism of action. Prior efforts characterized its cellular targets including neuron, glia and endothelial cells. We propose tDCS also modulates the substance transport in brain tissue. High resolution multiphoton microscopy imaged the spread across rat brain tissue of fluorescently-labeled solutes injected through the carotid artery after tDCS. The effective solute diffusion coefficient of brain tissue (D_eff) was determined from the spatio-temporal solute concentration profiles using an unsteady diffusion transport model. 5–10 min post 20 min–1 mA tDCS, D_eff increased by ~ 10% for a small solute, sodium fluorescein, and ~ 120% for larger solutes, BSA and Dex-70k. All increases in D_eff returned to the control level 25–30 min post tDCS. A mathematical model for D_eff in the extracelluar space (ECS) further predicts that this dose of tDCS increases D_eff by transiently enhancing the brain ECS gap spacing by ~ 1.5-fold and accordingly reducing the extracellular matrix density. The cascades leading ECS modulation and its impact on excitability, synaptic function, plasticity, and brain clearance require further study. Modulation of solute diffusivity and ECS could explain diverse outcomes of tDCS and suggest novel therapeutic strategies.

Transcranial electrical stimulation motor threshold can estimate individualized tDCS dosage from reverse-calculation electric-field modeling

Background:

Unique amongst brain stimulation tools, transcranial direct current stimulation (tDCS) currently lacks an easy or widely implemented method for individualizing dosage.

Objective:

We developed a method of reverse-calculating electric-field (E-field) models based on Magnetic Resonance Imaging (MRI) scans that can estimate individualized tDCS dose. We also evaluated an MRI-free method of individualizing tDCS dose by measuring transcranial magnetic stimulation (TMS) motor threshold (MT) and single pulse, suprathreshold transcranial electrical stimulation (TES) MT and regressing it against E-field modeling. Key assumptions of reverse-calculation E-field modeling, including the size of region of interest (ROI) analysis and the linearity of multiple E-field models were also tested.

Methods:

In 29 healthy adults, we acquired TMS MT, TES MT, and anatomical T1-weighted MPRAGE MRI scans with a fiducial marking the motor hotspot. We then computed a “reverse-calculated tDCS dose” of tDCS applied at the scalp needed to cause a 1.00 V/m E-field at the cortex. Finally, we examined whether the predicted E-field values correlated with each participant’s measured TMS MT or TES MT.

Results:

We were able to determine a reverse-calculated tDCS dose for each participant using a 5 × 5 x 5 voxel grid region of interest (ROI) approach (average = 6.03 mA, SD = 1.44 mA, range = 3.75–9.74 mA). The Transcranial Electrical Stimulation MT, but not the Transcranial Magnetic Stimulation MT, significantly correlated with the ROI-based reverse-calculated tDCS dose determined by E-field modeling (R² = 0.45, p < 0.001).

Conclusions:

Reverse-calculation E-field modeling, alone or regressed against TES MT, shows promise as a method to individualize tDCS dose. The large range of the reverse-calculated tDCS doses between subjects underscores the likely need to individualize tDCS dose. Future research should further examine the use of TES MT to individually dose tDCS as an MRI-free method of dosing tDCS.

Materials for blood brain barrier modeling in vitro

Brain homeostasis relies on the selective permeability property of the blood brain barrier (BBB). The BBB is formed by a continuous endothelium that regulates exchange between the blood stream and the brain. This physiological barrier also creates a challenge for the treatment of neurological diseases as it prevents most blood circulating drugs from entering into the brain. In vitro cell models aim to reproduce BBB functionality and predict the passage of active compounds through the barrier. In such systems, brain microvascular endothelial cells (BMECs) are cultured in contact with various biomaterial substrates. However, BMEC interactions with these biomaterials and their impact on BBB functions are poorly described in the literature. Here we review the most common materials used to culture BMECs and discuss their potential impact on BBB integrity in vitro. We investigate the biophysical properties of these biomaterials including stiffness, porosity and material degradability. We highlight a range of synthetic and natural materials and present three categories of cell culture dimensions: cell monolayers covering non-degradable materials (2D), cell monolayers covering degradable materials (2.5D) and vascularized systems developing into degradable materials (3D).

In Vivo Modulation of the Blood-Brain Barrier Permeability by Transcranial Direct Current Stimulation (tDCS)

tDCS has been used to treat various brain disorders and its mechanism of action (MoA) was found to be neuronal polarization. Since the blood-brain barrier (BBB) tightly regulates the neuronal microenvironment, we hypothesized that another MoA of tDCS is direct vascular activation by modulating the BBB structures to increase its permeability (P). To test this hypothesis, we used high resolution multiphoton microscopy to determine P of the cerebral microvessels in rat brain. We found that 20 min 0.1-1 mA tDCS transiently increases P to a small solute, sodium fluorescein (MW 376) and to a large solute, Dextran-70k, with a much higher increase in P to the large solute. By pretreating the vessel with a nitric oxide synthase inhibitor, we revealed that the tDCS-induced increase in P is NO dependent. A transport model for the BBB was further employed to predict the structural changes by the tDCS. Comparing model predictions with the measured data suggests that tDCS increases P by temporarily disrupting the structural components forming the paracellular pathway of the BBB. That the transient and reversible increase in the BBB permeability also suggests new applications of tDCS such as a non-invasive approach for brain drug delivery through the BBB.

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.

Iontophoresis in lateral epicondylitis: a randomized, double-blind clinical trial

BACKGROUND

Lateral epicondylitis (LE) is a painful condition typically caused by excessive use of tendons, resulting in tendinopathy, inflammation, pain, and sensitivity changes in the lateral elbow. Iontophoresis is a noninvasive method of systemic and local drug delivery by means of a current. The study aimed to evaluate the effects of iontophoresis in patients with LE.

METHODS

We performed a randomized, double-blind clinical trial. Twenty-four patients with LE, randomized into an iontophoresis group and a galvanic current group. The iontophoresis group received a solution of dexamethasone (4 mg/mL) and gel lidocaine-applied on the negative electrode by means of a continuous current at 5 mA for 15 minutes-and the positive electrode received a base gel solution. Patients in the galvanic current group received the same protocol but using a base gel solution on both electrodes.

RESULTS

Both groups showed a significant improvement in pain on exertion and rest; increased handgrip strength in elbow extension and flexion; and improved function, as evaluated by the Patient-Rated Tennis Elbow Evaluation scale (P < .05). Iontophoresis showed superior results compared with galvanic current in pain on exertion and rest and in the function of individuals with tennis elbow.

CONCLUSION

Iontophoresis proved to be an effective technique in reducing pain and improving strength and function in individuals with LE (tennis elbow).

Reduction of intratumoral brain perfusion by noninvasive transcranial electrical stimulation

Malignant brain neoplasms have a poor prognosis despite aggressive treatments. Animal models and evidence from human bodily tumors reveal that sustained reduction in tumor perfusion via electrical stimulation promotes tumor necrosis, therefore possibly representing a therapeutic option for patients with brain tumors. Here, we demonstrate that transcranial electrical stimulation (tES) allows to safely and noninvasively reduce intratumoral perfusion in humans. Selected patients with glioblastoma or metastasis underwent tES, while perfusion was assessed using magnetic resonance imaging. Multichannel tES was applied according to personalized biophysical modeling, to maximize the induced electrical field over the solid tumor mass. All patients completed the study and tolerated the procedure without adverse effects, with tES selectively reducing the perfusion of the solid tumor. Results potentially open the door to noninvasive therapeutic interventions in brain tumors based on stand-alone tES or its combination with other available therapies.

Implantable Direct Current Neural Modulation: Theory, Feasibility, and Efficacy

Implantable neuroprostheses such as cochlear implants, deep brain stimulators, spinal cord stimulators, and retinal implants use charge-balanced alternating current (AC) pulses to recover delivered charge and thus mitigate toxicity from electrochemical reactions occurring at the metal-tissue interface. At low pulse rates, these short duration pulses have the effect of evoking spikes in neural tissue in a phase-locked fashion. When the therapeutic goal is to suppress neural activity, implants typically work indirectly by delivering excitation to populations of neurons that then inhibit the target neurons, or by delivering very high pulse rates that suffer from a number of undesirable side effects. Direct current (DC) neural modulation is an alternative methodology that can directly modulate extracellular membrane potential. This neuromodulation paradigm can excite or inhibit neurons in a graded fashion while maintaining their stochastic firing patterns. DC can also sensitize or desensitize neurons to input. When applied to a population of neurons, DC can modulate synaptic connectivity. Because DC delivered to metal electrodes inherently violates safe charge injection criteria, its use has not been explored for practical applicability of DC-based neural implants. Recently, several new technologies and strategies have been proposed that address this safety criteria and deliver ionic-based direct current (iDC). This, along with the increased understanding of the mechanisms behind the transcutaneous DC-based modulation of neural targets, has caused a resurgence of interest in the interaction between iDC and neural tissue both in the central and the peripheral nervous system. In this review we assess the feasibility of in-vivo iDC delivery as a form of neural modulation. We present the current understanding of DC/neural interaction. We explore the different design methodologies and technologies that attempt to safely deliver iDC to neural tissue and assess the scope of application for direct current modulation as a form of neuroprosthetic treatment in disease. Finally, we examine the safety implications of long duration iDC delivery. We conclude that DC-based neural implants are a promising new modulation technology that could benefit from further chronic safety assessments and a better understanding of the basic biological and biophysical mechanisms that underpin DC-mediated neural modulation.