Noninvasive modulation of predictive coding in humans: causal evidence for frequency-specific temporal dynamics.

Increasing evidence indicates that the brain predicts sensory input based on past experiences, importantly constraining how we experience the world. Despite a growing interest on this framework, known as predictive coding, most of such approaches to multiple psychological domains continue to be theoretical or primarily provide correlational evidence. We here explored the neural basis of predictive processing using noninvasive brain stimulation and provide causal evidence of frequency-specific modulations in humans. Participants received 20 Hz (associated with top-down/predictions), 50 Hz (associated with bottom-up/prediction errors), or sham transcranial alternating current stimulation on the left dorsolateral prefrontal cortex while performing a social perception task in which facial expression predictions were induced and subsequently confirmed or violated. Left prefrontal 20 Hz stimulation reinforced stereotypical predictions. In contrast, 50 Hz and sham stimulation failed to yield any significant behavioral effects. Moreover, the frequency-specific effect observed was further supported by electroencephalography data, which showed a boost of brain activity at the stimulated frequency band. These observations provide causal evidence for how predictive processing may be enabled in the human brain, setting up a needed framework to understand how it may be disrupted across brain-related conditions and potentially restored through noninvasive methods.

Neuromodulation with transcranial focused ultrasound.

The understanding of brain function and the capacity to treat neurological and psychiatric disorders rest on the ability to intervene in neuronal activity in specific brain circuits. Current methods of neuromodulation incur a tradeoff between spatial focus and the level of invasiveness. Transcranial focused ultrasound (FUS) is emerging as a neuromodulation approach that combines noninvasiveness with focus that can be relatively sharp even in regions deep in the brain. This may enable studies of the causal role of specific brain regions in specific behaviors and behavioral disorders. In addition to causal brain mapping, the spatial focus of FUS opens new avenues for treatments of neurological and psychiatric conditions. This review introduces existing and emerging FUS applications in neuromodulation, discusses the mechanisms of FUS effects on cellular excitability, considers the effects of specific stimulation parameters, and lays out the directions for future work.

Design of NIRS Probe Based on Computational Model to Find Out the Optimal Location for Non-Invasive Brain Stimulation.

The paper presents a computational model to analyse the electric field distribution on the cerebral cortex during high definition transcranial direct current stimulation (HD-tDCS) technique. The current research aims to improve the focality in term of magnitude of electric field (norm [E]) and magnitude of current density (norm [J]) in the gyri and sulci of white matter. The proposed computational model is used to predict the magnitude of current density and magnitude of electric field distribution generated across the target region of cerebral cortex for specific small size 1 × 1 cm2 multi-electrode HD-tDCS configurations. The current works aims at optimizing the number of electrodes and current density for multielectrode HD-tDCS configuration and weak current intensity is obtained by calculating surface area and penetration depth of target region of cerebral cortex. In terms of surface area and penetration depth 4 × 1 HD-tDCS and 2 mA weak dc current configuration has been selected. The optimized 4 × 1 HD-tDCS configuration is placed on target location of the brain surface and the changes in the magnitude of current density and magnitude of electric field distribution is calculated at the different locations on brain surface including scalp surface, skull surface gray matter and white matter surface. The variation in magnitude electric field distribution is seen in the cerebrospinal fluid (CSF), gray and white matter surface of target cerebral cortex. Based on the insights received from the variation in the magnitude of current density and magnitude of electric field distribution, the design of an appropriate NIRS probe has been proposed to aid in non-invasive brain stimulation. Designed NIRS probe is based on distance of separation between source and photodetector to cover the affected area with 4 × 1 HD-tDCS technique and measurement sensitivity distribution at gray matter surface of cerebral cortex. The estimated percentage of pixel area of measurement sensitivity distribution is 17.094%, which confirm to cover the 7.9384% distributed pixel area in term of calculated magnitude of current density affected with 4 × 1 HD-tDCS configuration.

Combining non-invasive transcranial brain stimulation with neuroimaging and electrophysiology: Current approaches and future perspectives.

Non-invasive transcranial brain stimulation (NTBS) techniques such as transcranial magnetic stimulation (TMS) and transcranial current stimulation (TCS) are important tools in human systems and cognitive neuroscience because they are able to reveal the relevance of certain brain structures or neuronal activity patterns for a given brain function. It is nowadays feasible to combine NTBS, either consecutively or concurrently, with a variety of neuroimaging and electrophysiological techniques. Here we discuss what kind of information can be gained from combined approaches, which often are technically demanding. We argue that the benefit from this combination is twofold. Firstly, neuroimaging and electrophysiology can inform subsequent NTBS, providing the required information to optimize where, when, and how to stimulate the brain. Information can be achieved both before and during the NTBS experiment, requiring consecutive and concurrent applications, respectively. Secondly, neuroimaging and electrophysiology can provide the readout for neural changes induced by NTBS. Again, using either concurrent or consecutive applications, both "online" NTBS effects immediately following the stimulation and "offline" NTBS effects outlasting plasticity-inducing NTBS protocols can be assessed. Finally, both strategies can be combined to close the loop between measuring and modulating brain activity by means of closed-loop brain state-dependent NTBS. In this paper, we will provide a conceptual framework, emphasizing principal strategies and highlighting promising future directions to exploit the benefits of combining NTBS with neuroimaging or electrophysiology.

Using reciprocity for relating the simulation of transcranial current stimulation to the EEG forward problem.

To explore the relationship between transcranial current stimulation (tCS) and the electroencephalography (EEG) forward problem, we investigate and compare accuracy and efficiency of a reciprocal and a direct EEG forward approach for dipolar primary current sources both based on the finite element method (FEM), namely the adjoint approach (AA) and the partial integration approach in conjunction with a transfer matrix concept (PI). By analyzing numerical results, comparing to analytically derived EEG forward potentials and estimating computational complexity in spherical shell models, AA turns out to be essentially identical to PI. It is then proven that AA and PI are also algebraically identical even for general head models. This relation offers a direct link between the EEG forward problem and tCS. We then demonstrate how the quasi-analytical EEG forward solutions in sphere models can be used to validate the numerical accuracies of FEM-based tCS simulation approaches. These approaches differ with respect to the ease with which they can be employed for realistic head modeling based on MRI-derived segmentations. We show that while the accuracy of the most easy to realize approach based on regular hexahedral elements is already quite high, it can be significantly improved if a geometry-adaptation of the elements is employed in conjunction with an isoparametric FEM approach. While the latter approach does not involve any additional difficulties for the user, it reaches the high accuracies of surface-segmentation based tetrahedral FEM, which is considerably more difficult to implement and topologically less flexible in practice. Finally, in a highly realistic head volume conductor model and when compared to the regular alternative, the geometry-adapted hexahedral FEM is shown to result in significant changes in tCS current flow orientation and magnitude up to 45° and a factor of 1.66, respectively.

High-Frequency Transcranial Random Noise Stimulation Enhances Perception of Facial Identity.

Recently, a number of studies have demonstrated the utility of transcranial current stimulation as a tool to facilitate a variety of cognitive and perceptual abilities. Few studies, though, have examined the utility of this approach for the processing of social information. Here, we conducted 2 experiments to explore whether a single session of high-frequency transcranial random noise stimulation (tRNS) targeted at lateral occipitotemporal cortices would enhance facial identity perception. In Experiment 1, participants received 20 min of active high-frequency tRNS or sham stimulation prior to completing the tasks examining facial identity perception or trustworthiness perception. Active high-frequency tRNS facilitated facial identity perception, but not trustworthiness perception. Experiment 2 assessed the spatial specificity of this effect by delivering 20 min of active high-frequency tRNS to lateral occipitotemporal cortices or sensorimotor cortices prior to participants completing the same facial identity perception task used in Experiment 1. High-frequency tRNS targeted at lateral occipitotemporal cortices enhanced performance relative to motor cortex stimulation. These findings show that high-frequency tRNS to lateral occipitotemporal cortices produces task-specific and site-specific enhancements in face perception.

Cathodal HD-tDCS above the left dorsolateral prefrontal cortex increases environmentally sustainable decision-making.

Environmental sustainability is characterized by a conflict between short-term self-interest and longer-term collective interests. Self-control capacity has been proposed to be a crucial determinant of people's ability to overcome this conflict. Yet, causal evidence is lacking, and previous research is dominated by the use of self-report measures. Here, we modulated self-control capacity by applying inhibitory high-definition transcranial current stimulation (HD-tDCS) above the left dorsolateral prefrontal cortex (dlPFC) while participants engaged in an environmentally consequential decision-making task. The task includes conflicting and low conflicting trade-offs between short-term personal interests and long-term environmental benefits. Contrary to our preregistered expectation, inhibitory HD-tDCS above the left dlPFC, presumably by reducing self-control capacity, led to more, and not less, pro-environmental behavior in conflicting decisions. We speculate that in our exceptionally environmentally friendly sample, deviating from an environmentally sustainable default required self-control capacity, and that inhibiting the left dlPFC might have reduced participants' ability to do so.

Short-term Effect of Noninvasive Brain Stimulation Techniques on Motor Impairment in Chronic Ischemic Stroke: A Systematic Review with Meta-Analysis.

Background: In recent years, noninvasive brain stimulation (NIBS) has shown promise for stroke rehabilitation as a novel nonpharmaceutical neuromodulatory intervention with attractive neurophysiological theories backing it up. Objective: To find out the short-term effects of NIBS techniques on motor impairment in chronic ischemic stroke. Materials and Methods: A systematic review with meta-analysis was performed separately for transcranial direct current stimulation (tDCS), transcranial magnetic stimulation (TMS), and studies that combined both, utilizing various databases for a period spanning from 2001 to 2019. Good-quality randomized controlled trials (RCTs) on chronic ischemic stroke cases with homogeneous clinical upper motor short-term outcome measures were considered for the meta-analysis. RevMan 5.1 software was used for the meta-analysis. Meta-analysis registration: CRD42021196299; https://www.crd.york.ac.uk/PROSPERO. Results: A total of 319 studies were identified initially. After necessary filters to comply with the strict recruitment criteria, only four studies qualified, two each for tDCS and TMS and none qualified for analysis under the combined category. tDCS showed a nonsignificant effect on the upper limb motor function improvement (-0.10 [95% confidence interval {CI}: -0.84 to 0.64; I2 0%; P = 0.8]), whereas the repetitive TMS showed a significant effect (0.75 [95% CI: 0.03-1.48; I2 0%; P = 0.04]). The safety analysis did not reveal any major concerns for several published protocols. Conclusions: tDCS alone did not significantly benefit motor recovery; rTMS was effective in providing immediate functional benefits in chronic ischemic stroke. While the current stroke rehabilitation protocols with NIBS appear safe, more good-quality stratified RCTs with more innovative experimental protocols are needed to analyze and quantify the efficacy of these techniques in stroke rehabilitation.

Anodal high-definition transcranial direct current stimulation reduces heart rate and modulates heart-rate variability in healthy young people: A randomized cross-controlled trial.

Objective: To investigate whether anodal high-definition transcranial current stimulation (HD-tDCS) over the left dorsolateral pre-frontal cortex (DLPFC) could modulate the heart rate (HR) and heart-rate variability (HRV) in healthy young people. Methods: Forty healthy young people were enrolled in this randomized crossover trial. The participants were randomized to receive anodal HD-tDCS (n = 20) or sham HD-tDCS (n = 20) over the left DLPFC with a washout period of 1 week. Electrocardiogram (ECG) data were continuously recorded 20 min before the stimulation, during the session (20 min), and 20 min after the session. HR and the time- and frequency-domain indices of the HRV were measured to investigate the activity of the sympathetic and parasympathetic nervous systems. Results: Anodal HD-tDCS over the left DLPFC induced a significant decrease in HR and a significant increase in the average of normal-to-normal intervals (AVG NN), low-frequency (LF) power, total power (TP), and LF/high-frequency (HF) ratio in comparison with the sham stimulation and the baseline. However, sham HD-tDCS over the left DLPFC had no significant effect on HR or HRV. Conclusions: Anodal HD-tDCS over the left DLPFC could reduce HR and modulate the HRV in healthy young people. HD-tDCS may show some potential for acutely modulating cardiovascular function.

Transcranial current stimulation in epilepsy: A systematic review of the fundamental and clinical aspects.

Purpose: Transcranial electrical current stimulation (tES or tCS, as it is sometimes referred to) has been proposed as non-invasive therapy for pharmacoresistant epilepsy. This technique, which includes direct current (tDCS) and alternating current (tACS) stimulation involves the application of weak currents across the cortex to change cortical excitability. Although clinical trials have demonstrated the therapeutic efficacy of tES, its specific effects on epileptic brain activity are poorly understood. We sought to summarize the clinical and fundamental effects underlying the application of tES in epilepsy. Methods: A systematic review was performed in accordance with the PRISMA guidelines. A database search was performed in PUBMED, MEDLINE, Web of Science and Cochrane CENTRAL for articles corresponding to the keywords "epilepsy AND (transcranial current stimulation OR transcranial electrical stimulation)". Results: A total of 56 studies were included in this review. Through these records, we show that tDCS and tACS epileptic patients are safe and clinically relevant techniques for epilepsy. Recent articles reported changes of functional connectivity in epileptic patients after tDCS. We argue that tDCS may act by affecting brain networks, rather than simply modifying local activity in the targeted area. To explain the mechanisms of tES, various cellular effects have been identified. Among them, reduced cell loss, mossy fiber sprouting, and hippocampal BDNF protein levels. Brain modeling and human studies highlight the influence of individual brain anatomy and physiology on the electric field distribution. Computational models may optimize the stimulation parameters and bring new therapeutic perspectives. Conclusion: Both tDCS and tACS are promising techniques for epilepsy patients. Although the clinical effects of tDCS have been repeatedly assessed, only one clinical trial has involved a consistent number of epileptic patients and little knowledge is present about the clinical outcome of tACS. To fill this gap, multicenter studies on tES in epileptic patients are needed involving novel methods such as personalized stimulation protocols based on computational modeling. Furthermore, there is a need for more in vivo studies replicating the tES parameters applied in patients. Finally, there is a lack of clinical studies investigating changes in intracranial epileptiform discharges during tES application, which could clarify the nature of tES-related local and network dynamics in epilepsy.

Challenging control over emotions in borderline personality disorder - a tDCS study.

BACKGROUND: Deficient cognitive control (CC) over emotional distraction is a central characteristic of borderline personality disorder (BPD). Reduced activation of the left dorsolateral prefrontal cortex (dlPFC) has been linked to this deficit. This study investigates whether it is possible to ameliorate CC deficits via anodal tDCS over the left dlPFC in BPD. Furthermore, we investigate whether the extent of CC impairment influences how well one responds to tDCS. METHODS: The effect of a single-session tDCS (1 mA for 20 min, reference electrode on the contralateral mastoid bone) to the left dlPFC (F3) on the CC of patients with BPD (N = 20) and healthy control participants (HCs, N = 20) was examined in a double-blinded, balanced randomized, sham-controlled crossover trial. A delayed response working memory task with negative, neutral and positive pictures presented during the delay period was conducted to assess CC. Stimulation was applied simultaneously with the task. RESULTS: Negative pictures caused prolonged response times as compared to a control condition in patients with BPD and HCs. Anodal tDCS to the left dlPFC did not significantly reduce this interference effect in the overall sample. Further analyses showed, however, that participants with impaired CC profited the most from anodal tDCS. In the subgroup of participants who actually showed an interference effect we found the expected significant amelioration of CC under tDCS. CONCLUSIONS: The present study demonstrates that anodal tDCS applied to the left dlPFC improves deficient CC. Thereby, base-level performance moderates tDCS effects. Hence, tDCS might be suitable to support behavioral trainings to enhance CC specifically in people whose impairments in CC are comparably high.

Using Probabilistic Movement Primitives in Analyzing Human Motion Differences Under Transcranial Current Stimulation.

In medical tasks such as human motion analysis, computer-aided auxiliary systems have become the preferred choice for human experts for their high efficiency. However, conventional approaches are typically based on user-defined features such as movement onset times, peak velocities, motion vectors, or frequency domain analyses. Such approaches entail careful data post-processing or specific domain knowledge to achieve a meaningful feature extraction. Besides, they are prone to noise and the manual-defined features could hardly be re-used for other analyses. In this paper, we proposed probabilistic movement primitives (ProMPs), a widely-used approach in robot skill learning, to model human motions. The benefit of ProMPs is that the features are directly learned from the data and ProMPs can capture important features describing the trajectory shape, which can easily be extended to other tasks. Distinct from previous research, where classification tasks are mostly investigated, we applied ProMPs together with a variant of Kullback-Leibler (KL) divergence to quantify the effect of different transcranial current stimulation methods on human motions. We presented an initial result with 10 participants. The results validate ProMPs as a robust and effective feature extractor for human motions.

Augmentation of EMDR with multifocal transcranial current stimulation (MtCS) in the treatment of fibromyalgia: study protocol of a double-blind randomized controlled exploratory and pragmatic trial.

BACKGROUND: Fibromyalgia (FM) is a generalized, widespread chronic pain disorder affecting 2.7% of the general population. In recent years, different studies have observed a strong association between FM and psychological trauma. Therefore, a trauma-focused psychotherapy, such as eye movement desensitization and reprocessing (EMDR), combined with a non-invasive brain stimulation technique, such as multifocal transcranial current stimulation (MtCS), could be an innovative adjunctive treatment option. This double-blind randomized controlled trial (RCT) analyzes if EMDR therapy is effective in the reduction of pain symptoms in FM patients and if its potential is boosted with the addition of MtCS. METHODS: Forty-five patients with FM and a history of traumatic events will be randomly allocated to Waiting List, EMDR + active-MtCS, or EMDR + sham-MtCS. Therapists and patients will be kept blind to MtCS conditions, and raters will be kept blind to both EMDR and MtCS. All patients will be evaluated at baseline, post-treatment, and follow-up at 6 months after post-treatment. Evaluations will assess the following variables: sociodemographic data, pain, psychological trauma, sleep disturbance, anxiety and affective symptoms, and wellbeing. DISCUSSION: This study will provide evidence of whether EMDR therapy is effective in reducing pain symptoms in FM patients, and whether the effect of EMDR can be enhanced by MtCS. TRIAL REGISTRATION: ClinicalTrials.gov NCT04084795 . Registered on 2 August 2019.

A comprehensive analysis of the impact of head model extent on electric field predictions in transcranial current stimulation.

Objective.MRI-based head models are used to predict the electric field (E-field) in the brain in transcranial current stimulation. The standard field of view of clinical MRI often only covers the head down to the skull base, which has usually lead to models truncated at the level of the nose. Although recent pipelines can artificially extend the head model to the neck, the need for implementing full head models preserving skull holes such as the foramen magnum remains controversial. The objective of this work is to analyse the impact of head model extent on E-field accuracy, with emphasis on specific electrode montages.Approach. A full head model containing an open foramen magnum and a cut head model with closed skull were compared in terms of predicted E-field. Several electrode montages, including fronto-occipital montages recently used in validation studies, were simulated. Local and global metrics were used to evaluate the error for both E-field magnitude and distribution, along with tangential and normal components over different cortical areas. The percentage of current flowing through the lower head was also computed.Results. Regarding E-field magnitude, small relative differences (RDs) below 7% were found in grey matter for classical montages. Although considerably higher RDs near 50% were found for fronto-occipital montages, absolute errors of 0.1 V m-1were only found in non-targeted regions such as the cerebellum. Differences in tangential and normal E-fields were similar and followed the same trend observed for E-field magnitude. Our results also showed a high correlation between the percentage of current shunted through the lower head and the absolute E-field differences.Significance. The influence of head model extent on E-field accuracy depends on electrode montage. Standard cut head models provide sufficiently accurate predictions for both E-field magnitude and distribution in targeted brain areas. However, fronto-occipital montages exhibited larger errors, which might be considered in further validation studies.

Effectiveness of language training and non-invasive brain stimulation on oral and written naming performance in Primary Progressive Aphasia: A meta-analysis and systematic review.

The aim of this systematic review and meta-analysis is to examine the efficacy of language training, alone or in combination with non-invasive brain stimulation techniques, designed to improve oral and written naming abilities in Primary Progressive Aphasia (PPA), and to investigate whether gains can be maintained over time and generalize to untrained items. An electronic database search was conducted up to 31st of May 2019. Forty-three articles on language training alone and seven articles on the combined treatment fitted the inclusion criteria for the systematic review. Results indicated that language training, alone or in combination with transcranial direct current stimulation (tDCS), improves oral naming accuracy for trained items in patients with PPA, with a long-term maintenance of the gain over time. Only language training combined with tDCS improves oral naming accuracy for untrained items. Considering written naming abilities, language training combined with tDCS improves performance for both trained and untrained items, immediately after training and at follow-up.

The electroencephalographic features of the sleep onset process and their experimental manipulation with sleep deprivation and transcranial electrical stimulation protocols.

The sleep onset (SO) process is characterized by gradual electroencephalographic (EEG) changes. The interest for the possibility to manipulate the electrophysiological pattern of the wake-sleep transition is recently growing. This review aims to describe the EEG modifications of the SO process in healthy humans and the evidence about their experimental manipulation. We provide an overview of the electrophysiological changes during the wake-sleep transition, considering several methods to study the EEG signals. We then describe the impact of sleep deprivation (SD) on the electrophysiology of SO. Finally, we discuss the evidence about the possibility to modulate the local EEG activity through transcranial current stimulation protocols with the aim to promote, hinder, or manipulate the electrophysiological mechanisms of the wake-sleep transition. The reviewed findings highlight the local nature of the EEG processes during the SO and their intensification and speedup after SD. The evidence about the possibility to non-invasively affect the EEG pattern of the wake-sleep transition may have important implications for clinical conditions that would benefit from its prevention or promotion.

Transcranial Alternating Current Stimulation With the Theta-Band Portion of the Temporally-Aligned Speech Envelope Improves Speech-in-Noise Comprehension.

Transcranial alternating current stimulation with the speech envelope can modulate the comprehension of speech in noise. The modulation stems from the theta- but not the delta-band portion of the speech envelope, and likely reflects the entrainment of neural activity in the theta frequency band, which may aid the parsing of the speech stream. The influence of the current stimulation on speech comprehension can vary with the time delay between the current waveform and the audio signal. While this effect has been investigated for current stimulation based on the entire speech envelope, it has not yet been measured when the current waveform follows the theta-band portion of the speech envelope. Here, we show that transcranial current stimulation with the speech envelope filtered in the theta frequency band improves speech comprehension as compared to a sham stimulus. The improvement occurs when there is no time delay between the current and the speech stimulus, as well as when the temporal delay is comparatively short, 90 ms. In contrast, longer delays, as well as negative delays, do not impact speech-in-noise comprehension. Moreover, we find that the improvement of speech comprehension at no or small delays of the current stimulation is consistent across participants. Our findings suggest that cortical entrainment to speech is most influenced through current stimulation that follows the speech envelope with at most a small delay. They also open a path to enhancing the perception of speech in noise, an issue that is particularly important for people with hearing impairment.

Transcranial Current Stimulation Alters the Expression of Immune-Mediating Genes.

Despite its extensive use in clinical studies, the molecular mechanisms underlying the effects of transcranial direct current stimulation (tDCS) remain to be elucidated. We previously described subacute effects of tDCS on immune- and stem cells in the rat brain. To investigate the more immediate effects of tDCS regulating those cellular responses, we treated rats with a single session of either anodal or cathodal tDCS, and analyzed the gene expression by microarray; sham-stimulated rats served as control. Anodal tDCS increased expression of several genes coding for the major histocompatibility complex I (MHC I), while cathodal tDCS increased the expression of the immunoregulatory protein osteopontin (OPN). We confirmed the effects of gene upregulation by immunohistochemistry at the protein level. Thus, our data show a novel mechanism for the actions of tDCS on immune- and inflammatory processes, providing a target for future therapeutic studies.

Update on current and emerging therapies for dystonia.

Treatment strategies for dystonia depend on the focal, segmental or generalized distribution of symptoms. Chemodenervation with botulinum toxin remains the treatment of choice for focal- or select-body regions in generalized and segmental dystonia. A potentially longer acting formulation of botulinum toxin is being investigated besides the currently available formulations. Electromyography increases toxin injection accuracy and may reduce injection number, frequency, side effects and costs by identifying dystonic muscle activity. Oral anticholinergics, baclofen and clonazepam are used off-label, but novel drugs in development include sodium oxybate, zonisamide and perampanel. Characterizing dystonia as a sensorimotor circuit disorder has prompted the use of noninvasive neuromodulation procedures. These techniques need further study but simultaneous rehabilitation techniques appear to also improve outcomes. Pallidal deep-brain stimulation is beneficial for medication-refractory primary generalized and possibly focal dystonia such as cervical dystonia. Certain genetic conditions are amenable to specific therapies and future gene-targeted therapies could benefit selected dystonia patients.

Does 10-Hz Cathodal Oscillating Current of the Parieto-Occipital Lobe Modulate Target Detection?

The phase of alpha (8-12 Hz) brain oscillations have been associated with moment to moment changes in visual attention and awareness. Previous work has demonstrated that endogenous oscillations and subsequent behavior can be modulated by oscillating transcranial current stimulation (otCS). The purpose of the current study is to establish the efficacy of cathodal otCS for modulation of the ongoing alpha brain oscillations, allowing for modulation of individual's visual perception. Thirty-six participants performed a target detection with sham and 10-Hz cathodal otCS. Each participant had two practice and two experimental sets composed of three blocks of 128 trials per block. Stimulating electrodes were placed on the participant's head with the anode electrode at Cz and the cathode electrode at Oz. A 0.5 mA current was applied every 100 ms (10 Hz frequency) during the otCS condition. The same current and frequency was applied for the first 10-20 s of the sham condition, after which the current was turned off. Target detection rates were compared between the sham and otCS experimental conditions in order to test for effects of otCS phase on target detection. We found no significant difference in target detection rates between the sham and otCS conditions, and discuss potential reasons for the apparent inability of cathodal otCS to effectively modulate visual perception.