Transcranial Random Noise Stimulation Research Articles

Enhancement of phonemic verbal fluency in multilingual young adults by transcranial random noise stimulation

Several studies have analyzed the effects of transcranial direct current stimulation on verbal fluency tasks in non-clinical populations. Nevertheless, the reported effects on verbal fluency are inconsistent. In addition, the effect of other techniques such as transcranial random noise stimulation (tRNS) on verbal fluency enhancement has yet to be studied in healthy multilingual populations. This study aims to explore the effects of tRNS on verbal fluency in healthy multilingual individuals. Fifty healthy multilingual (Spanish, English and Basque) adults were randomly assigned to a tRNS or sham group. Electrodes were placed on the left dorsolateral prefrontal cortex and left inferior frontal gyrus. All participants performed phonemic and semantic verbal fluency tasks before, during (online assessment) and immediately after (offline assessment) stimulation in three different languages. The results showed significantly better performance by participants who received tRNS in the phonemic verbal fluency tasks in Spanish (in the online and offline assessment) and English (in the offline assessment). No differences between conditions were found in Basque nor semantic verbal fluency. These findings suggests that tRNS on the left prefrontal cortex could help improve phonemic, yet not semantic, fluency in healthy multilingual adults.

Transcranial random noise stimulation (tRNS) improves hot and cold executive functions in children with attention deficit-hyperactivity disorder (ADHD)

Children with attention deficit-hyperactivity disorder (ADHD) have impaired hot and cold executive functions, which is thought to be related to impaired ventromedial and dorsolateral prefrontal cortex (vmPFC and dlPFC) functions. The present study aimed to assess the impact concurrent stimulation of dlPFC and vmPFC through transcranial random noise stimulation (tRNS), a non-invasive brain stimulation tool which enhances cortical excitability via application of alternating sinusoidal currents with random frequencies and amplitudes over the respective target regions on hot and cold executive functions. Eighteen children with ADHD received real and sham tRNS over the left dlPFC and the right vmPFC in two sessions with one week interval. The participants performed Circle Tracing, Go/No-Go, Wisconsin Card Sorting, and Balloon Analogue Risk Tasks during stimulation in each session. The results showed improved ongoing inhibition, prepotent inhibition, working memory, and decision making, but not set-shifting performance, during real, as compared to sham stimulation. This indicates that simultaneous stimulation of the dlPFC and the vmPFC improves hot and cold executive functions in children with ADHD.

Exploring the Prospects of Transcranial Electrical Stimulation (tES) as a Therapeutic Intervention for Post-Stroke Motor Recovery: A Narrative Review.

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

Transcranial Random Noise Stimulation in the Management of Cognitive and Behavioral Symptoms in a Suicidal Hanging Survivor: A Case Study.

Transcranial Random Noise Stimulation in the Management of Cognitive and Behavioral Symptoms in a Suicidal Hanging Survivor: A Case Study.

No Frequency-Specific Effect of Transcranial Random Noise Stimulation on Resting EEG.

Transcranial random noise stimulation (tRNS) is a form of noninvasive transcranial electrical stimulation that applies alternating current in various randomized frequencies to the cortex, thereby improving cognitive functioning in multiple domains. However, the precise mechanism of tRNS, as well as its impact on human electroencephalography (EEG), remains unclear. This is partly because most studies have used tRNS in conjunction with a cognitive task, making it difficult to tease apart whether the observed changes in EEG are a result of tRNS, the cognitive task, or their interaction. Forty-nine healthy individuals participated in this study and were randomly assigned to active tRNS (n = 24) and sham (n = 25) groups. tRNS was delivered for 20 minutes over Fp1/Fp2 and Oz. Resting-state EEG data were collected before and after either tRNS or sham stimulation. Cluster-based permutation tests using FieldTrip revealed no frequency-specific effect of tRNS on resting-state EEG data across four frequency bands (theta, alpha, beta, gamma). These observations suggest that tRNS itself does not target or alter specific EEG frequencies. Rather, tRNS most likely interacts with the cognitive task/activity at hand to produce an observable difference in post-tRNS EEG. Positive tRNS-EEG findings from previous studies are also likely to have resulted from the interactive and cognitive activity-dependent nature of tRNS.

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.

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. 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. 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.

Mechanistic account of the left auditory cortex for tone-matching in schizophrenia: A pilot transcranial random noise stimulation (tRNS) sham-controlled study

ObjectiveDeficits in the ability to match tones following brief delay and their contribution to higher-order cognitive alterations have been repeatedly documented in schizophrenia. The aim was to explore if left fronto-temporal high-frequency transcranial random noise stimulation (hf-tRNS), with electrodes placed over brain regions involved in tone-matching would significantly modulate performances in participants with schizophrenia. MethodsIn a randomized, double-blind sham-controlled study, 10 participants with schizophrenia were allocated to receive ten sessions of either active or sham hf-tRNS. The anode was placed over the left prefrontal cortex and the cathode over the left temporoparietal junction. A tone-matching task was administered before and after the hf-tRNS. ResultsWe calculated the changes in tone-matching performance before and after hf-tRNS session in each group. A significant between-group difference was observed for the difficult tone-matching conditions (W= 14.500, p = 0.032), with tone-matching improvement in the sham group and no improvement in the active group. Discussionhf-tRNS could disrupt the test-retest learning effect in the tone-matching task in individuals with schizophrenia. It is likely that this disruption resulted from cathodal-induced inhibition of the functional coupling between auditory cortical areas that correlates with tone-matching performance in patients. ConclusionThe findings contribute to our understanding of hf-tRNS effects on early auditory processing in schizophrenia.

Single sessions of transcranial direct current stimulation and transcranial random noise stimulation exert no effect on sleepiness in patients with narcolepsy and idiopathic hypersomnia.

Hypersomnia poses major challenges to treatment providers given the limitations of available treatment options. In this context, the application of non-invasive brain stimulation techniques such as transcranial electrical stimulation (tES) may open up new avenues to effective treatment. Preliminary evidence suggests both acute and longer-lasting positive effects of transcranial direct current stimulation (tDCS) on vigilance and sleepiness in hypersomniac patients. Based on these findings, the present study sought to investigate short-term effects of single sessions of tDCS and transcranial random noise stimulation (tRNS) on sleepiness in persons suffering from hypersomnia. A sample of 29 patients suffering from narcolepsy or idiopathic hypersomnia (IH) was recruited from the Regensburg Sleep Disorder Center and underwent single sessions of tES (anodal tDCS, tRNS, sham) over the left and right dorsolateral prefrontal cortex on three consecutive days in a double-blind, sham-controlled, pseudorandomized crossover trial. The primary study endpoint was the mean reaction time measured by the Psychomotor Vigilance Task (PVT) before and directly after the daily tES sessions. Secondary endpoints were additional PVT outcome metrics as well as subjective outcome parameters (e.g., Karolinska Sleepiness Scale; KSS). There were no significant treatment effects neither on objective (i.e., PVT) nor on subjective indicators of sleepiness. We could not demonstrate any clinically relevant effects of single sessions of tDCS or tRNS on objective or subjective measures of sleepiness in patients with hypersomnia. However, we cannot exclude that repeated sessions of tES may affect vigilance or sleepiness in hypersomniac patients.

Effects of transcranial electrical stimulation of the right posterior parietal cortex on physical control responses

The posterior parietal cortex plays an important role in postural stability by adapting to changes in input from the visual, vestibular, and proprioceptive systems. However, little is known regarding whether transcranial electrical stimulation of the posterior parietal cortex affects reactive postural responses. This study aimed to investigate changes in physical control responses to anodal and cathodal transcranial direct current stimulation and transcranial random noise stimulation of the right posterior parietal cortex using a simultaneous inertial measurement unit. The joint movements of the lower limb of 33 healthy volunteers were measured while standing on a soft-foam surface with eyes closed during various stimulation modalities. These modalities included anodal, cathodal transcranial direct current stimulation, and sham stimulation in Experiment 1, and transcranial random noise and sham stimulations in Experiment 2. The results showed that cathodal stimulation significantly decreased the joint angular velocity in the hip rotation, ankle inversion-eversion, and abduction–adduction directions compared to anodal or sham stimulation in Experiment 1. In contrast, there were no significant differences in physical control responses with transcranial random noise stimulation coeducation in Experiment 2. These findings suggest that transcranial electrical stimulation of the right posterior parietal cortex may modulate physical control responses; however, the effect depends on the stimulus modality.

Effects of transcranial direct current stimulation and transcranial random noise stimulation on working memory and task-related EEG in major depressive disorder

ObjectiveTo compare effects of transcranial direct current stimulation (tDCS) and transcranial random noise stimulation with a direct-current offset (tRNS + DC-offset) on working memory (WM) performance and task-related electroencephalography (EEG) in individuals with Major Depressive Disorder (MDD). MethodsUsing a sham-controlled, parallel-groups design, 49 participants with MDD received either anodal tDCS (N = 16), high-frequency tRNS + DC-offset (N = 16), or sham stimulation (N = 17) to the left dorsolateral prefrontal cortex (DLPFC) for 20-minutes. The Sternberg WM task was completed with concurrent EEG recording before and at 5- and 25-minutes post-stimulation. Event-related synchronisation/desynchronisation (ERS/ERD) was calculated for theta, upper alpha, and gamma oscillations during WM encoding and maintenance. ResultstDCS significantly increased parieto-occipital upper alpha ERS/ERD during WM maintenance, observed on EEG recorded 5- and 25-minutes post-stimulation. tRNS + DC-offset did not significantly alter WM-related oscillatory activity when compared to sham stimulation. Neither tDCS nor tRNS + DC-offset improved WM performance to a significantly greater degree than sham stimulation. ConclusionsAlthough tDCS induced persistent effects on WM-related oscillatory activity, neither tDCS nor tRNS + DC-offset enhanced WM performance in MDD. SignificanceThis reflects the first sham-controlled comparison of tDCS and tRNS + DC-offset in MDD. These findings directly contrast with evidence of tRNS-induced enhancements in WM in healthy individuals.

69 Transcranial Random Noise Stimulation Facilitates Phonemic Verbal Fluency and Convergent Thinking in Multilingual Healthy Adults.

Objective:The aim of the present study was to analyse the effects of the transcranial random noise stimulation (tRNS) technique when placed on the left dorsolateral prefrontal cortex (L-DPFC) and left inferior frontal gyrus (L-IFG), for the improvement of verbal fluency performance and creativity skills in a group of multilingual healthy adults.Participants and Methods:Fifty healthy adults, aged 18-47 years, participated in the study. All of them were native Spanish speakers of which three were bilingual (Spanish and English) and 47 were multilingual (Spanish, Basque and English). The study had a randomized, counterbalanced, double-blind, sham-controlled design. The participants were randomly allocated to either a tRNS active group or a placebo-control group. All participants were tested individually in one session divided into three parts: (1) baseline, (2) online, and (3) offline assessment. In the active condition, a 1.5mA current (100-500 Hz) was delivered for 20 minutes (online phase). Participants’ verbal fluency was assessed through semantic and phonemic verbal fluency tasks in three different languages (Spanish, Basque and English), while creativity was assessed in their native language with the Remote Associations Test (RAT, pre and post forms) for convergent thinking, and with the Unusual Uses subtest (UU, pre and post forms) for divergent thinking. In addition, the linguistic profile of the participants was evaluated with the Language Experience and Proficiency Questionnaire (LEAP-Q), and their processing speed and cognitive flexibility were assessed with the Stroop Color and Word Test (SCWT).Results:The results showed significant differences in phonemic fluency between the groups during the online assessment in Spanish (F= 5.31, p = 0.026), and in the offline assessments in Spanish (F=6.44, p = 0.015) and English (F=10.80, p = 0.002), with participants in the active condition performing better. While no differences were observed in the performance of the groups in verbal fluency in Basque, neither in the online (F=1.06, p = 0.31), nor in the offline assessment (F=2.62, p = 0.11). Furthermore, no significant differences were observed between groups in semantic verbal fluency tasks in any of the languages, neither during stimulation nor offline. However, there were no differences between conditions in the online (Spanish, F=0.86, p = 0.35; English, F=2.95, p = 0.09; and Basque, F=0.01 p = 0.94) and offline (Spanish, F=2.53, p = 0.11; English, F=0.74, p = 0.39; and Basque, F=1.39, p = 0.24) semantic tasks. In creativity, significant differences were observed between groups on the RAT (F=9.58, p = 0.003), while no differences were observed in the performance of any of the three dimensions of the UU (Originality, F=0.44, p = 0.51; Flexibility, F=0.42, p = 0.51; Fluency, F=0.69, p = 0.41). In the SCWT, statistically significant differences were only observed in the colour-word part (F=7.60, p = 0.008) during the online assessment, showing a better performance of the participants under the tRNS condition compare to the sham condition.Conclusions:The results obtained in this study suggest that the excitatory effects of tRNS over the L-DLPFC L-IFG could contribute to the improvement of phonemic verbal fluency and verbal convergent thinking, in healthy individuals.

Characterising modulatory effects of high-intensity high frequency transcranial random noise stimulation using the perceptual template model

Neural noise is an inherent property of all nervous systems. However, our understanding of the mechanisms by which noise influences perception is still limited. To elucidate this relationship, we require techniques that can safely modulate noise in humans. Transcranial random noise stimulation (tRNS) has been proposed to induce noise into cortical processing areas according to the principles of stochastic resonance (SR). Specifically, it has been demonstrated that small to moderate intensities of noise improve performance. To date, however, high intensity tRNS effects on neural noise levels have not been directly quantified, nor have the detrimental effects proposed by SR been demonstrated in early visual function. Here, we applied 3 mA high-frequency tRNS to primary visual cortex during an orientation-discrimination task across increasing external noise levels and used the Perceptual Template Model to quantify the mechanisms by which noise changes perceptual performance in healthy observers. Results show that, at a group level, high-intensity tRNS worsened perceptual performance. Our computational analysis reveals that this change in performance was underpinned by an increased amount of additive noise and a reduced ability to filter external noise compared to sham stimulation. Interestingly, while most observers experienced detrimental effects, a subset of participants demonstrated improved performance. Preliminary evidence suggests that differences in baseline internal noise levels might account for these individual differences. Together, these results refine our understanding of the mechanisms underlying the influence of neural noise on perception and have important implications for the application of tRNS as a research tool.

Non-invasive brain stimulation on clinical symptoms in multiple sclerosis patients: A systematic review and meta-analysis.

Non-invasive brain stimulation (NIBS) has demonstrated mixed effects on the clinical symptoms of multiple sclerosis. This systematic review and meta-analysis aimed to evaluate the effects of NIBS techniques on the most common symptoms of MS. A literature search was performed until October 2022 which included randomized controlled trials and quasi-experimental studies that used sham-controlled NIBS in patients with MS. We calculated the Hedge's effect sizes of each domain of interest and their 95% confidence intervals (95% CIs) and performed random effects meta-analyses. A total of 49 studies were included in the systematic review (944 participants). Forty-four eligible studies were included for quantitative analysis, of which 33 applied transcranial direct current stimulation (tDCS), 9 transcranial magnetic stimulation (TMS), and 2 transcranial random noise stimulation (tRNS). We found a significant decrease in fatigue (ES: -0.86, 95% CI: -1.22 to-0.51, p<0.0001), pain (ES:-1.91, 95% CI,-3.64 to-0.19, p=0.03) and psychiatric symptoms (ES:-1.44, 95% CI-2.56 to-0.32, p=0.01) in favor of tDCS compared with the sham. On the other hand, there was no strong evidence showing tDCS effectiveness on motor performance and cognition (ES:-0.03, 95% CI-0.35 to 0.28, p=0.83 and ES: 0.71, 95% CI,-0.09 to 1.52, p=0.08, respectively). Regarding TMS, we found a significant decrease in fatigue (ES:-0.45, 95% CI:-0.84 to -0.07, p=0.02) and spasticity levels (ES:-1.11, 95% CI:-1.48 to-0.75, p<0.00001) compared to the sham. However, there was no strong evidence of the effectiveness of TMS on motor performance (ES:-0.39, 95% CI-0.95 to 0.16, p=0.16). Finally, there was no significant evidence showing the effectiveness of tRNS on fatigue levels (ES:-0.28, 95% CI:-1.02 to 0.47, p=0.46) and cognitive improvement (ES:-0.04, 95% CI:-0.6, 0.52, p=0.88) compared with the sham. Overall, most studies have investigated the effects of tDCS on MS symptoms, particularly fatigue. The symptom that most benefited from NIBS was fatigue, while the least to benefit was motor performance. In addition, we found that disability score was associated with fatigue improvement. Thus, these findings support the idea that NIBS could have some promising effects on specific MS symptoms. It is also important to underscore that studies are very heterogeneous regarding the parameters of stimulation, and this may also have influenced the effects on some specific behavioral domains.

Human neuronal excitation/inhibition balance explains and predicts neurostimulation induced learning benefits.

Previous research has highlighted the role of the excitation/inhibition (E/I) ratio for typical and atypical development, mental health, cognition, and learning. Other research has highlighted the benefits of high-frequency transcranial random noise stimulation (tRNS)-an excitatory form of neurostimulation-on learning. We examined the E/I as a potential mechanism and studied whether tRNS effect on learning depends on E/I as measured by the aperiodic exponent as its putative marker. In addition to manipulating E/I using tRNS, we also manipulated the level of learning (learning/overlearning) that has been shown to influence E/I. Participants (n = 102) received either sham stimulation or 20-minute tRNS over the dorsolateral prefrontal cortex (DLPFC) during a mathematical learning task. We showed that tRNS increased E/I, as reflected by the aperiodic exponent, and that lower E/I predicted greater benefit from tRNS specifically for the learning task. In contrast to previous magnetic resonance spectroscopy (MRS)-based E/I studies, we found no effect of the level of learning on E/I. A further analysis using a different data set suggest that both measures of E/I (EEG versus MRS) may reflect, at least partly, different biological mechanisms. Our results highlight the role of E/I as a marker for neurostimulation efficacy and learning. This mechanistic understanding provides better opportunities for augmented learning and personalized interventions.

Transcranial random noise stimulation combined with cognitive training for treating ADHD: a randomized, sham-controlled clinical trial

Non-invasive brain stimulation has been suggested as a potential treatment for improving symptomology and cognitive deficits in Attention-Deficit/Hyperactivity Disorder (ADHD), the most common childhood neurodevelopmental disorder. Here, we examined whether a novel form of stimulation, high-frequency transcranial random noise stimulation (tRNS), applied with cognitive training (CT), may impact symptoms and neural oscillations in children with ADHD. We conducted a randomized, double-blind, sham-controlled trial in 23 unmedicated children with ADHD, who received either tRNS over the right inferior frontal gyrus (rIFG) and left dorsolateral prefrontal cortex (lDLPFC) or sham stimulation for 2 weeks, combined with CT. tRNS + CT yielded significant clinical improvements (reduced parent-reported ADHD rating-scale scores) following treatment, compared to the control intervention. These improvements did not change significantly at a 3-week follow-up. Moreover, resting state (RS)-EEG periodic beta bandwidth of the extracted peaks was reduced in the experimental compared to control group immediately following treatment, with further reduction at follow-up. A lower aperiodic exponent, which reflects a higher cortical excitation/inhibition (E/I) balance and has been related to cognitive improvement, was seen in the experimental compared to control group. This replicates previous tRNS findings in adults without ADHD but was significant only when using a directional hypothesis. The experimental group further exhibited longer sleep onset latencies and more wake-up times following treatment compared to the control group. No significant group differences were seen in executive functions, nor in reported adverse events. We conclude that tRNS + CT has a lasting clinical effect on ADHD symptoms and on beta activity. These results provide a preliminary direction towards a novel intervention in pediatric ADHD.

The effect of visual statistical learning on proactive motor control is modulated by transcranial random noise stimulation over frontoparietal cortex.

The effect of visual statistical learning on proactive motor control is modulated by transcranial random noise stimulation over frontoparietal cortex.

The effects of transcranial electrical stimulation of the left dorsolateral prefrontal cortex on tactile spatial discrimination performance

The dorsolateral prefrontal cortex (DLPFC) plays a key role in tactile perceptual discrimination performance. Both transcranial random noise stimulation (tRNS) and anodal transcranial pulsed current stimulation (tPCS) have been shown to modulate neural activity in cortical regions. In this study, we aimed to determine whether tRNS and anodal tPCS over the left DLPFC would improve tactile perceptual discrimination performance of the right index finger in healthy neurological individuals. Subjects underwent a grating orientation task before, immediately after, and 30 min after applying tRNS in Experiment 1 or anodal tPCS in Experiment 2. tRNS application on the left DLPFC tended to enhance tactile perceptual discrimination performance. In contrast, the application of anodal tPCS over the left DLPFC did not affect tactile perceptual discrimination performance. These findings indicate that transcranial electrical stimulation to the left DLPFC may improve tactile perceptual discrimination performance, with effects that depend on stimulus modality.

The effect of emotion intensity on time perception: a study with transcranial random noise stimulation

Emotional facial expressions provide cues for social interactions and emotional events can distort our sense of time. The present study investigates the effect of facial emotional stimuli of anger and sadness on time perception. Moreover, to investigate the causal role of the orbitofrontal cortex (OFC) in emotional recognition, we employed transcranial random noise stimulation (tRNS) over OFC and tested the effect on participants’ emotional recognition as well as on time processing. Participants performed a timing task in which they were asked to categorize as “short” or “long” temporal intervals marked by images of people expressing anger, sad or neutral emotional facial expressions. In addition, they were asked to judge if the image presented was of a person expressing anger or sadness. The visual stimuli were facial emotional stimuli indicating anger or sadness with different degrees of intensity at high (80%), medium (60%) and low (40%) intensity, along with neutral emotional face stimuli. In the emotional recognition task, results showed that participants were faster and more accurate when emotional intensity was higher. Moreover, tRNS over OFC interfered with emotion recognition, which is in line with its proposed role in emotion recognition. In the timing task, participants overestimated the duration of angry facial expressions, although neither emotional intensity not OFC stimulation significantly modulated this effect. Conversely, as the emotional intensity increased, participants exhibited a greater tendency to overestimate the duration of sad faces in the sham condition. However, this tendency disappeared with tRNS. Taken together, our results are partially consistent with previous findings showing an overestimation effect of emotionally arousing stimuli, revealing the involvement of OFC in emotional distortions of time, which needs further investigation.

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.