Effects of Short-Term Random Noise Electrical Stimulation on Dissociated Pyramidal Neurons from the Cerebral Cortex

Effects of online tDCS and hf-tRNS on reading performance in children and adolescents with developmental dyslexia: a study protocol for a cross sectional, within-subject, randomized, double-blind, and sham-controlled trial

Background

Developmental Dyslexia (DD) is a brain-based developmental disorder causing severe reading difficulties. The extensive data on the neurobiology of DD have increased interest in brain-directed approaches, such as transcranial direct current stimulation (tDCS), which have been proposed for DD. While positive outcomes have been observed, results remain heterogeneous. Various methodological approaches have been employed to address this issue. However, no studies have compared the effects of different transcranial electrical stimulation techniques (e.g., tDCS and transcranial random noise stimulation, tRNS), on reading in children and adolescents with DD.

Methods

The present within-subject, double-blind, and sham-controlled trial aims to investigate the effects of tDCS and hf-tRNS on reading in children and adolescents with DD. Participants will undergo three conditions with a one-week interval session: (A) single active tDCS session; (B) single active hf-tRNS session; and (C) single sham session (tDCS/hf-tRNS). Left anodal/right cathodal tDCS and bilateral tRNS will be applied over the temporo-parietal regions for 20 min each. Reading measures will be collected before and during each session. Safety and blinding parameters will be recordered.

Discussion

We hypothesize that tRNS will demonstrate comparable effectiveness to tDCS in improving reading compared to sham conditions. Additionally, we anticipate that hf-tRNS will exhibit a similar safety profile to tDCS. This study will contribute novel insights into the effectiveness of hf-tRNS, expediting the validation of brain-based treatments for DD.

tRNS boosts visual perceptual learning in participants with bilateral macular degeneration

Perceptual learning (PL) has shown promise in enhancing residual visual functions in patients with age-related macular degeneration (MD), however it requires prolonged training and evidence of generalization to untrained visual functions is limited. Recent studies suggest that combining transcranial random noise stimulation (tRNS) with perceptual learning produces faster and larger visual improvements in participants with normal vision. Thus, this approach might hold the key to improve PL effects in MD. To test this, we trained two groups of MD participants on a contrast detection task with (n = 5) or without (n = 7) concomitant occipital tRNS. The training consisted of a lateral masking paradigm in which the participant had to detect a central low contrast Gabor target. Transfer tasks, including contrast sensitivity, near and far visual acuity, and visual crowding, were measured at pre-, mid and post-tests. Combining tRNS and perceptual learning led to greater improvements in the trained task, evidenced by a larger increment in contrast sensitivity and reduced inhibition at the shortest target to flankers' distance. The overall amount of transfer was similar between the two groups. These results suggest that coupling tRNS and perceptual learning has promising potential applications as a clinical rehabilitation strategy to improve vision in MD patients.

Contrast detection is enhanced by deterministic, high-frequency transcranial alternating current stimulation with triangle and sine waveform

Stochastic resonance (SR) describes a phenomenon where an additive noise (stochastic carrier-wave) enhances the signal transmission in a nonlinear system. In the nervous system, nonlinear properties are present from the level of single ion channels all the way to perception and appear to support the emergence of SR. For example, SR has been repeatedly demonstrated for visual detection tasks, also by adding noise directly to cortical areas via transcranial random noise stimulation (tRNS). When dealing with nonlinear physical systems, it has been suggested that resonance can be induced not only by adding stochastic signals (i.e., noise) but also by adding a large class of signals that are not stochastic in nature that cause "deterministic amplitude resonance" (DAR). Here, we mathematically show that high-frequency, deterministic, periodic signals can yield resonance-like effects with linear transfer and infinite signal-to-noise ratio at the output. We tested this prediction empirically and investigated whether nonrandom, high-frequency, transcranial alternating current stimulation (tACS) applied to the visual cortex could induce resonance-like effects and enhance the performance of a visual detection task. We demonstrated in 28 participants that applying 80-Hz triangular-waves or sine-waves with tACS reduced the visual contrast detection threshold for optimal brain stimulation intensities. The influence of tACS on contrast sensitivity was equally effective to tRNS-induced modulation, demonstrating that both tACS and tRNS can reduce contrast detection thresholds. Our findings suggest that a resonance-like mechanism can also emerge when deterministic electrical waveforms are applied via tACS.NEW & NOTEWORTHY Our findings extend our understanding of neuromodulation induced by noninvasive electrical stimulation. We provide the first evidence showing acute online benefits of transcranial alternating current stimulation (tACS)triangle and tACSsine targeting the primary visual cortex (V1) on visual contrast detection in accordance with the resonance-like phenomenon. The "deterministic" tACS and "stochastic" high-frequency-transcranial random noise stimulation (tRNS) are equally effective in enhancing visual contrast detection.

The effects of transcranial random noise stimulation on motor function: A comprehensive review of the literature

The present review considers all papers published on the topic up to the end of the year 2022. Transcranial random noise stimulation (tRNS) is a non-invasive neuromodulation technique introduced about 15 years ago whose use is becoming increasingly widespread in neuroscience. It consists of the application over the scalp of a weak, white noise-like current, through electrodes having a surface of several square centimetres, for a duration ranging from seconds to minutes. Despite its relatively low spatial and temporal resolution, tRNS has well defined effects on central motor excitability, which critically depend on stimulation parameters. These effects seem to be chiefly based on an effect on neuronal membrane sodium channels and can last much longer than the stimulation itself. While the effects at the cellular level in the motor cortex are becoming progressively clear, much more studies are needed to understand the effects of tRNS on motor behaviour and performance, where initial research results are nevertheless promising, in both basic and applied research.

Transcranial random noise stimulation to augment hand function in individuals with moderate-to-severe stroke: A pilot randomized clinical trial

Background

Interventions to recover upper extremity (UE) function after moderate-to-severe stroke are limited. Transcranial random noise stimulation (tRNS) is an emerging non-invasive technique to improve neuronal plasticity and may potentially augment functional outcomes when combined with existing interventions, such as functional electrical stimulation (FES).

Objective

The objective of this study was to investigate the feasibility and preliminary efficacy of combined tRNS and FES-facilitated task practice to improve UE impairment and function after moderate-to-severe stroke.

Methods

Fourteen individuals with UE weakness were randomized into one of two groups: 1) tRNS with FES-facilitated task practice, or 2) sham-tRNS with FES-facilitated task practice. Both groups involved 18 intervention sessions (3 per week for 6 weeks). tRNS was delivered at 2 mA current between 100-500 Hz for the first 30 minutes of FES-facilitated task practice. We evaluated the number of sessions completed, adverse effects, participant satisfaction, and intervention fidelity between the two therapists. UE impairment (Fugl-Meyer Upper Extremity, FMUE), function (Wolf Motor Function Test, WMFT), participation (Stroke Impact Scale hand score, SIS-H), and grip strength were assessed at baseline, within 1 week and 3 months after completing the intervention.

Results

All participants completed the 18 intervention sessions. Participants reported minimal adverse effects (mild tingling in head). The two trained therapists demonstrated 93% adherence and 96% competency with the intervention protocol. FMUE and SIS-H improved significantly more in the tRNS group than in the sham-tRNS group at both timepoints (p≤0.05), and the differences observed exceeded the clinically meaningful differences for these scores. The WMFT and paretic hand grip strength improved in both groups after the intervention (p≤0.05), with no significant between group differences.

Conclusion

Our findings show for the first time that combining tRNS and FES-facilitated task practice is a feasible and promising approach to improve UE impairment and function after moderate-to-severe stroke.

Using noise for the better: The effects of transcranial random noise stimulation on the brain and behavior

Van der Groen, O., Potok, W., Wenderoth, N., Edwards, G., Mattingley, J.B. and Edwards, D. Using noise for the better: The effects of transcranial random noise stimulation on the brain and behavior. NEUROSCI BIOBEHAV REV X (X) XXX-XXX 2021.- Transcranial random noise stimulation (tRNS) is a non-invasive electrical brain stimulation method that is increasingly employed in studies of human brain function and behavior, in health and disease. tRNS is effective in modulating perception acutely and can improve learning. By contrast, its effectiveness for modulating higher cognitive processes is variable. Prolonged stimulation with tRNS, either as one longer application, or multiple shorter applications, may engage plasticity mechanisms that can result in long-term benefits. Here we provide an overview of the current understanding of the effects of tRNS on the brain and behavior and provide some specific recommendations for future research.

Stochastic and sinusoidal electrical stimuli increase the irregularity and gain of Type A and B medial vestibular nucleus neurons, in vitro

Galvanic vestibular stimulation (GVS) has been shown to improve vestibular function potentially via stochastic resonance, however, it remains unknown how central vestibular nuclei process these signals. In vivo work applying electrical stimuli to the vestibular apparatus of animals has shown changes in neuronal discharge at the level of the primary vestibular afferents and hair cells. This study aimed to determine the cellular impacts of stochastic, sinusoidal, and stochastic + sinusoidal stimuli on individual medial vestibular nucleus (MVN) neurons of male and female C57BL/6 mice. All stimuli increased the irregularity of MVN neuronal discharge, while differentially affecting neuronal gain. This suggests that the heterogeneous MVN neuronal population (marked by differential expression of ion channels), may influence the impact of electrical stimuli on neuronal discharge. Neuronal subtypes showed increased variability of neuronal firing, where Type A and B neurons experienced the largest gain changes in response to stochastic and sinusoidal stimuli. Type C neurons were the least affected regarding neuronal firing variability and gain changes. The membrane potential (MP) of neurons was altered by sinusoidal and stochastic + sinusoidal stimuli, with Type B and C neuronal MP significantly affected. These results indicate that GVS-like electrical stimuli impact MVN neuronal discharge differentially, likely as a result of heterogeneous ion channel expression.

Transcranial Random Noise Stimulation Acutely Lowers the Response Threshold of Human Motor Circuits

Transcranial random noise stimulation (tRNS) over cortical areas has been shown to acutely improve performance in sensory detection tasks. One explanation for this behavioral effect is stochastic resonance (SR), a mechanism that explains how signal processing in nonlinear systems can benefit from added noise. While acute noise benefits of electrical RNS have been demonstrated at the behavioral level as well as in in vitro preparations of neural tissue, it is currently largely unknown whether similar effects can be shown at the neural population level using neurophysiological readouts of human cortex. Here, we hypothesized that acute tRNS will increase the responsiveness of primary motor cortex (M1) when probed with transcranial magnetic stimulation (TMS). Neural responsiveness was operationalized via the well-known concept of the resting motor threshold (RMT). We showed that tRNS acutely decreases RMT. This effect was small, but it was consistently replicated across four experiments including different cohorts (total N = 81, 46 females, 35 males), two tRNS electrode montages, and different control conditions. Our experiments provide critical neurophysiological evidence that tRNS can acutely generate noise benefits by enhancing the neural population response of human M1.SIGNIFICANCE STATEMENT A hallmark feature of stochastic resonance (SR) is that signal processing can benefit from added noise. This has mainly been demonstrated at the single-cell level in vitro where the neural response to weak input signals can be enhanced by simultaneously applying random noise. Our finding that transcranial random noise stimulation (tRNS) acutely increases the excitability of corticomotor circuits extends the principle of noise benefits to the neural population level in human cortex. Our finding is in line with the notion that tRNS might affect cortical processing via the SR phenomenon. It suggests that enhancing the response of cortical populations to an external stimulus might be one neurophysiological mechanism mediating performance improvements when tRNS is applied to sensory cortex during perception tasks.

Noisy Light Augments the Na+ Current in Somatosensory Pyramidal Neurons of Optogenetic Transgenic Mice

In previous reports, we developed a method to apply Brownian optogenetic noise-photostimulation (BONP, 470 nm) up to 0.67 mW on the barrel cortex of in vivo ChR2 transgenic mice. In such studies, we found that the BONP produces an increase in the evoked field potentials and the neuronal responses of pyramidal neurons induced by somatosensory mechanical stimulation. Here we extended such findings by examining whether the same type of BONP augments the Na⁺ current amplitude elicited by voltage-clamp ramps of dissociated pyramidal neurons from the somatosensory cortex of ChR2 transgenic and wild type mice. We found that in all neurons from the ChR2 transgenic mice, but none of the wild type mice, the peak amplitude of a TTX-sensitive Na⁺ current and its inverse of latency exhibited inverted U-like graphs as a function of the BONP level. It means that an intermediate level of BONP increases both the peak amplitude of the Na⁺ current and its inverse of latency. Our research suggests that the impact of BONP on the Na⁺ channels of pyramidal neurons could be associated with the observed augmentation-effects in our previous in vivo preparation. Moreover, it provides caution information for the use of an appropriate range of light intensity, <0.67 mW, which could avoid opto non-genetics (also termed “optonongenetic”) related responses due to light-induced temperature changes.

Inconsistent effects of stochastic resonance on human auditory processing

It has been demonstrated that, while otherwise detrimental, noise can improve sensory perception under optimal conditions. The mechanism underlying this improvement is stochastic resonance. An inverted U-shaped relationship between noise level and task performance is considered as the signature of stochastic resonance. Previous studies have proposed the existence of stochastic resonance also in the human auditory system. However, the reported beneficial effects of noise are small, based on a small sample, and do not confirm the proposed inverted U-shaped function. Here, we investigated in two separate studies whether stochastic resonance may be present in the human auditory system by applying noise of different levels, either acoustically or electrically via transcranial random noise stimulation, while participants had to detect acoustic stimuli adjusted to their individual hearing threshold. We find no evidence for behaviorally relevant effects of stochastic resonance. Although detection rate for near-threshold acoustic stimuli appears to vary in an inverted U-shaped manner for some subjects, it varies in a U-shaped manner or in other manners for other subjects. Our results show that subjects do not benefit from noise, irrespective of its modality. In conclusion, our results question the existence of stochastic resonance in the human auditory system.

tRNS effects on visual contrast detection

In recent years, transcranial electrical stimulation (tES) has been used to improve cognitive and perceptual abilities and to boost learning. In the visual domain, transcranial random noise stimulation (tRNS), a type of tES in which electric current is randomly alternating in between two electrodes at high frequency, has shown potential in inducing long lasting perceptual improvements when coupled with tasks such as contrast detection. However, its cortical mechanisms and online effects have not been fully understood yet, and it is still unclear whether these long-term improvements are due to early-stage perceptual enhancements of contrast sensitivity or later stage mechanisms such as learning consolidation. Here we tested tRNS effects on multiple spatial frequencies and orientation, showing that tRNS enhances detection of a low contrast Gabor, but only for oblique orientation and high spatial frequency (12 cycles per degree of visual angle). No improvement was observed for low contrast and vertical stimuli. These results indicate that tRNS can enhance contrast sensitivity already after one training session, however this early onset is dependent on characteristics of the stimulus such as spatial frequency and orientation. In particular, the shallow depth of tRNS is likely to affect superficial layers of the visual cortex where neurons have higher preferred spatial frequencies than cells in further layers, while the lack of effect on vertical stimuli might reflect the optimization of the visual system to see cardinally oriented low contrast stimuli, leaving little room for short-term improvement. Taken together, these results suggest that online tRNS effects on visual perception are the result of a complex interaction between stimulus intensity and cortical anatomy, consistent with previous literature on brain stimulation.

Excitatory and inhibitory lateral interactions effects on contrast detection are modulated by tRNS

Contrast sensitivity for a Gabor signal is affected by collinear high-contrast Gabor flankers. The flankers reduce (inhibitory effect) or increase (facilitatory effect) sensitivity, at short (2λ) and intermediate (6λ) target-to-flanker separation respectively. We investigated whether these inhibitory/facilitatory sensitivity effects are modulated by transcranial random noise stimulation (tRNS) applied to the occipital and frontal cortex of human observers during task performance. Signal detection theory was used to measure sensitivity (d’) and the Criterion (C) in a contrast detection task, performed with sham or tRNS applied over the occipital or the frontal cortex. After occipital stimulation results show a tRNS-dependent increased sensitivity for the single Gabor signal of low but not high contrast. Moreover, results suggest a dissociation of the tRNS effect when the Gabor signal is presented with the flankers, consisting in a general increased sensitivity at 2λ where the flankers had an inhibitory effect (reduction of inhibition) and a decreased sensitivity at 6λ where the flankers had a facilitatory effect on the Gabor signal (reduction of facilitation). After a frontal stimulation, no specific effect of the tRNS was found. We account for these complex interactions between tRNS and flankers by assuming that tRNS not only enhances feedforward input from the Gabor signal to the cortex, but also enhances the excitatory or inhibitory lateral intracortical input from the flankers. The boosted lateral input depends on the excitation-inhibition (E/I) ratio, namely when the lateral input is weak, it is boosted by tRNS with consequent modification of the contrast-dependent E/I ratio.

Transcranial random noise stimulation (tRNS): a wide range of frequencies is needed for increasing cortical excitability

Transcranial random noise stimulation (tRNS) is a recent neuromodulation protocol. The high-frequency band (hf-tRNS) has shown to be the most effective in enhancing neural excitability. The frequency band of hf-tRNS typically spans from 100 to 640 Hz. Here we asked whether both the lower and the higher half of the high-frequency band are needed for increasing neural excitability. Three frequency ranges (100–400 Hz, 400–700 Hz, 100–700 Hz) and Sham conditions were delivered for 10 minutes at an intensity of 1.5 mA over the primary motor cortex (M1). Single-pulse transcranial magnetic stimulation (TMS) was delivered over the same area at baseline, 0, 10, 20, 30, 45 and 60 minutes after stimulation, while motor evoked potentials (MEPs) were recorded to evaluate changes in cortical excitability. Only the full-band condition (100–700 Hz) was able to modulate excitability by enhancing MEPs at 10 and 20 minutes after stimulation: neither the higher nor the lower sub-range of the high-frequency band significantly modulated cortical excitability. These results show that the efficacy of tRNS is strictly related to the width of the selected frequency range.