We report a noninvasive strategy for electrically stimulating neurons at depth. By delivering to the brain multiple electric fields at frequencies too high to recruit neural firing, but which differ ...by a frequency within the dynamic range of neural firing, we can electrically stimulate neurons throughout a region where interference between the multiple fields results in a prominent electric field envelope modulated at the difference frequency. We validated this temporal interference (TI) concept via modeling and physics experiments, and verified that neurons in the living mouse brain could follow the electric field envelope. We demonstrate the utility of TI stimulation by stimulating neurons in the hippocampus of living mice without recruiting neurons of the overlying cortex. Finally, we show that by altering the currents delivered to a set of immobile electrodes, we can steerably evoke different motor patterns in living mice.
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•Noninvasive TI stimulation electrically stimulates neurons at depth selectively•Neurons are stimulated by interference between multiple electric fields•Neurons in mouse hippocampus can be stimulated without affecting the overlying cortex
A noninvasive method for deep-brain stimulation may be a new approach for the treatment of neuropsychiatric diseases.
Highlights • The application of low intensity TES in humans appears to be safe. • The profile of AEs in terms of frequency, magnitude and type is comparable in different populations. • Structured ...checklists and interviews as recommended procedures are provided in this paper.
Highlights • A review of technical aspects of transcranial electrical stimulation (tES) techniques. • Recommendations for safe and replicable application of tDCS and other tES methods. • Discussion ...of state-of-the-art methodology and design considerations in tES.
Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technique that applies low amplitude current via electrodes placed on the scalp. Rather than directly eliciting a ...neuronal response, tDCS is believed to modulate excitability-enhancing or suppressing neuronal activity in regions of the brain depending on the polarity of stimulation. The specificity of tDCS to any therapeutic application derives in part from how electrode configuration determines the brain regions that are stimulated. Conventional tDCS uses two relatively large pads (>25 cm(2)) whereas high-definition tDCS (HD-tDCS) uses arrays of smaller electrodes to enhance brain targeting. The 4 × 1 concentric ring HD-tDCS (one center electrode surrounded by four returns) has been explored in application where focal targeting of cortex is desired. Here, we considered optimization of concentric ring HD-tDCS for targeting: the role of electrodes in the ring and the ring's diameter. Finite element models predicted cortical electric field generated during tDCS. High resolution MRIs were segmented into seven tissue/material masks of varying conductivities. Computer aided design (CAD) model of electrodes, gel, and sponge pads were incorporated into the segmentation. Volume meshes were generated and the Laplace equation (Formula: see text · (σ Formula: see text V) = 0) was solved for cortical electric field, which was interpreted using physiological assumptions to correlate with stimulation and modulation. Cortical field intensity was predicted to increase with increasing ring diameter at the cost of focality while uni-directionality decreased. Additional surrounding ring electrodes increased uni-directionality while lowering cortical field intensity and increasing focality; though, this effect saturated and more than 4 surround electrode would not be justified. Using a range of concentric HD-tDCS montages, we showed that cortical region of influence can be controlled while balancing other design factors such as intensity at the target and uni-directionality. Furthermore, the evaluated concentric HD-tDCS approaches can provide categorical improvements in targeting compared to conventional tDCS. Hypothesis driven clinical trials, based on specific target engagement, would benefit by this more precise method of stimulation that could avoid potentially confounding brain regions.
Highlights • A group of European experts reviewed current evidence for therapeutic efficacy of tDCS. • Level B evidence (probable efficacy) was found for fibromyalgia, depression and craving. • The ...therapeutic relevance of tDCS needs to be further explored in these and other indications.
Highlights • This article reports on the safety of transcranial Direct Current Stimulation (tDCS), based on published Serious Adverse Effects in human trials and irreversible brain damage in animal ...models • Doses of tDCS sessions are defined and categorized by the electrode montage (skin contact area/size and position of all electrodes), stimulation intensity and duration • To date, the use of conventional tDCS protocols in human trials (≤40 min, ≤4 mA, ≤7.2 C) has not produced any reports of a Serious Adverse Effect or irreversible injury across over 33,200 sessions and 1,000 subjects with repeated sessions
Highlights • We review investigations of whether tDCS can facilitate motor skill learning and adaptation. • We identify several caveats in the existing literature and propose solutions for addressing ...these. • Open Science efforts will improve standardization, reproducibility and quality of future research.
The non-invasive delivery of electric currents through the scalp (transcranial electrical stimulation) is a popular tool for neuromodulation, mostly due to its highly adaptable nature (waveform, ...montage) and tolerability at low intensities (< 2 mA). Applied rhythmically, transcranial alternating current stimulation (tACS) may entrain neural oscillations in a frequency- and phase-specific manner, providing a causal perspective on brain–behaviour relationships. While the past decade has seen many behavioural and electrophysiological effects of tACS that suggest entrainment-mediated effects in the brain, it has been difficult to reconcile such reports with the weak intracranial field strengths (< 1 V/m) achievable at conventional intensities. In this review, we first describe the ongoing challenges faced by users of tACS. We outline the biophysics of electrical brain stimulation and the factors that contribute to the weak field intensities achievable in the brain. Since the applied current predominantly shunts through the scalp—stimulating the nerves that innervate it—the plausibility of transcutaneous (rather than transcranial) effects of tACS is also discussed. In examining the effects of tACS on brain activity, the complex problem of salvaging electrophysiological recordings from artefacts of tACS is described. Nevertheless, these challenges by no means mark the rise and fall of tACS: the second part of this review outlines the recent advancements in the field. We describe some ways in which artefacts of tACS may be better managed using high-frequency protocols, and describe innovative methods for current interactions within the brain that offer either dynamic or more focal current distributions while also minimising transcutaneous effects.
Highlights • We meta-analyzed 233 within-subject experiments investigating the effect of single-session DLPFC tDCS on cognitive outcomes. • No main effects of cathodal tDCS on reaction time, nor ...response accuracy were found. • No effects of stimulation parameters on cathodal tDCS effects on cognition were found. • Anodal tDCS significantly decreased response time in healthy participants, and increased response accuracy in neuropsychiatric patients. • In healthy participants, increased current densities/charges are associated to increased a-tDCS effects on response accuracy. • In neuropsychiatric patients, online task performance is associated to increased a-tDCS effects on accuracy, compared to offline task performance.
Transcranial direct current stimulation (tDCS) uses electrode pads placed on the head to deliver weak direct current to the brain and modulate neuronal excitability. The effects depend on the ...intensity and spatial distribution of the electric field. This in turn depends on the geometry and electric properties of the head tissues and electrode pads. Previous numerical studies focused on providing a reasonable level of detail of the head anatomy, often using simplified electrode models. Here, we explore via finite element method (FEM) simulations based on a high-resolution head model how detailed electrode modeling influences the calculated electric field in the brain. We take into account electrode shape, size, connector position and conductivities of different electrode materials (including saline solutions and electrode gels). These factors are systematically characterized to demonstrate their impact on the field distribution in the brain. The goals are to assess the effect of simplified electrode models; and to develop practical rules-of-thumb to achieve a stronger stimulation of the targeted brain regions underneath the electrode pads. We show that for standard rectangular electrode pads, lower saline and gel conductivities result in more homogeneous fields in the region of interest (ROI). Placing the connector at the center of the electrode pad or farthest from the second electrode substantially increases the field strength in the ROI. Our results highlight the importance of detailed electrode modeling and of having an adequate selection of electrode pads/gels in experiments. We also advise for a more detailed reporting of the electrode montages when conducting tDCS experiments, as different configurations significantly affect the results.
•Realistic modeling of the electrode pads used in tDCS•The electrode properties have a strong impact on the electric field in the brain.•The generated fields differ markedly from those predicted by simplified models.•Electrode and gel properties should be carefully selected and reported.
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