Transcranial Electrical Stimulation Studies Research Articles

Can visual cortex non-invasive brain stimulation improve normal visual function? A systematic review and meta-analysis.

Multiple studies have explored the use of visual cortex non-invasive brain stimulation (NIBS) to enhance visual function. These studies vary in sample size, outcome measures, and methodology. We conducted a systematic review and meta-analyses to assess the effects of NIBS on visual functions in human participants with normal vision. We followed the PRISMA guidelines, and a review protocol was registered with PROSPERO before study commencement (CRD42021255882). We searched Embase, Medline, PsychInfo, PubMed, OpenGrey and Web of Science using relevant keywords. The search covered the period from 1st January 2000 until 1st September 2021. Comprehensive meta-analysis (CMA) software was used for quantitative analysis. Fifty studies were included in the systematic review. Only five studies utilized transcranial magnetic stimulation (TMS) and no TMS studies met our pre-specified criteria for meta-analysis. Nineteen transcranial electrical stimulation studies (tES, 38%) met the criteria for meta-analysis and were the focus of our review. Meta-analysis indicated acute effects (Hedges's g = 0.232, 95% CI: 0.023-0.442, p = 0.029) and aftereffects (0.590, 95% CI: 0.182-0.998, p = 0.005) of tES on contrast sensitivity. Visual evoked potential (VEP) amplitudes were significantly enhanced immediately after tES (0.383, 95% CI: 0.110-0.665, p = 0.006). Both tES (0.563, 95% CI: 0.230-0.896, p = 0.001) and anodal-transcranial direct current stimulation (a-tDCS) alone (0.655, 95% CI: 0.273-1.038, p = 0.001) reduced crowding in peripheral vision. The effects of tES on visual acuity, motion perception and reaction time were not statistically significant. There are significant effects of visual cortex tES on contrast sensitivity, VEP amplitude, an index of cortical excitability, and crowding among normally sighted individuals. Additional studies are required to enable a comparable meta-analysis of TMS effects. Future studies with robust experimental designs are needed to extend these findings to populations with vision loss. ClinicalTrials.gov/, identifier CRD42021255882.

Neuromodulating the performance monitoring network during conflict and error processing in healthy populations: Insights from transcranial electric stimulation studies.

The performance monitoring system is fundamentally important for adapting one’s own behavior in conflicting and error-prone, highly demanding circumstances. Flexible behavior requires that neuronal populations optimize information processing through efficient multi-scale communication. Non-invasive brain stimulation (NIBS) studies using transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (tES) fields to alter the cortical activity promise to illuminate the neurophysiological mechanisms that underpin neuro-cognitive and behavioral processing and their causal relationship. Here, we focus on the transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS) that have been increasingly used in cognitive neuroscience for modulating superficial neural networks in a polarity (tDCS) and frequency/phase (tACS) fashion. Specifically, we discuss recent evidence showing how tDCS and tACS modulate the performance monitoring network in neurotypical samples. Emphasis is given to studies using behavioral tasks tapping conflict and error processing such as the Stroop, the Flanker, and the Simon tasks. The crucial role of mid-frontal brain regions (such as the medial frontal cortex, MFC; and the dorsal anterior cingulate cortex, dACC) and of theta synchronization in monitoring conflict and error is highlighted. We also discuss current technological limitations (e.g., spatial resolution) and the specific methodological strategies needed to properly modulate the cortical and subcortical regions.

RBIO-04. NEW THERAPEUTIC DELIVERY METHODS FOR TUMOR-TREATING FIELDS FOR HIGHER EFFICACY

Abstract Tumor-treating fields (TTFields) are the fourth modality of glioblastoma (GBM) treatment and in conjunction with chemotherapy can increase overall survival of GBM patients up to 60 months. However, in vitro and in animal models TTFields show 100% efficacy on a variety of tumor cell types including GBM cells when field strength is 4 V/cm, versus ~2 V/cm that is the clinical delivery target, TTFields are delivered transcranially. TTFields finite element modeling studies, supported by similar transcranial electric stimulation studies, show that the principal obstacle to delivering 4 V/cm is the electrically resistive skull. Our modeling shows the biophysics is more complicated than these findings. For instance, electrically-conductive cerebrospinal fluid regions surrounding the grey matter and in ventricles shunt electric current from anode to cathode, hindering delivery of the current required to produce 4 V/cm at the tumor/peritumor target. Thus, we consider two new delivery methods for TTFields. First, the transcranial array can be made more focal and directional, following modeling and development of electrode arrays used in spinal cord and deep brain stimulation. Our finite element modeling shows that similarly-designed TTFields electrode arrays can deliver field strength focally to a tumor target approaching 4 V/cm. Second, pre- or post-resection, TTFields can be delivered via electrode arrays surgically placed in the tumor or tumor resection cavity (intra-tumoral delivery), circumventing the resistive skull and CSF shunting effects. Such intra-tumoral arrays can deliver 4 V/cm to the tumor/peritumor region, opening up the potential to replicate clinically the 100% efficacy of TTFields in vitro and in animal models. Thus, new TTFields delivery may lead to unlimited survival of GMB patients via a side-effect free treatment modality.

P12-F Blinding of MRI based-individualized electrode montages for modulating excitability of the somatosensory cortex by tACS

Background Most transcranial electrical stimulation studies have been performed at the motor cortex due to easy mapping and easy excitability outread both by THere we target the sensory cortex with a multichannel stimulation array for the purpose of excitability modulation by tACS at the source level. We assume that stimulation can be optimized with precise location of the targeted source and using this information for guiding current flow into the cortex. Methods EEG and MRI data were collected from seven participants to reconstruct the P20/N20 source in the Brodmann area 3b. Real stimulation of tACS was optimized to the source using 140 Hz at 1 mA for 10minutes with 8 mm diameter EGI electrodes. A new sham protocol was developed with 1 ms pulse stimulation for 10 s (0.5 Hz) at 0.2 mA. FDM and eLORETA were used to generate an optimized source based tACS electrode montage. Results Total current density at the skin in the real stimulation montage varies from 0.365 mA/cm2 to 0.539 mA/cm2 which is about 10 times higher than standard 35 cm2 (0.029 mA/cm2) and 16 cm2 (0.062 mA/cm2) electrodes. On the other hand, the current density of the sham protocol was 0.0077 mA/cm2 to 0.0175 mA/cm2 which is 1.4 to 3.1 times higher than with the 35 cm2 electrode (0.0057 mA/cm2). Even with higher current density, with multiple electrodes used here a lesser amount of discomfort feeling was reported (real stimulation = 67% of participants reported with mild to moderate itching and warm; sham = 60% claimed to feel mildly warm and itchy). Conclusion Multichannel electrodes with higher current densities per electrode induce a more focal stimulation as compared to standard rubber electrodes. Stimulation was tolerable and provided better blinding.

Erratum to: Cognitive Enhancement of Numerical and Arithmetic Capabilities: a Mini-Review of Available Transcranial Electric Stimulation Studies

Erratum to: Cognitive Enhancement of Numerical and Arithmetic Capabilities: a Mini-Review of Available Transcranial Electric Stimulation Studies

Cognitive Enhancement of Numerical and Arithmetic Capabilities: a Mini-Review of Available Transcranial Electric Stimulation Studies

Arithmetic capabilities are complex cognitive skills essential for handling requirements of the modern world. At the same time, educational institutions are challenged with math-related problems, e.g., developmental dyscalculia and math anxiety, and also with less severe difficulties of arithmetic understanding. Thus, non-invasive techniques for cognitive enhancement have attracted researchers’ and practitioners’ interest in the fields of education, psychology, and neuroscience. Particularly, studies employing transcranial electric stimulation (tES) in arithmetic learning, problem solving, and performance in numerical tasks and operations have shaped an optimistic perspective of cognitive enhancement in these domains, building on the fronto-parietal correlates of healthy and deficient arithmetic performance and learning. However, the heterogeneity of stimulation approaches in numerical cognition research—with different electrode montages, stimulation protocols, tasks, outcomes, and combinations thereof—may also showcase a variety of parameters relevant more generally to the cognitive domain. Here, we present a short overview of the different tES approaches to enhance numerical and arithmetic capabilities in performance and training within the general framework of cognitive enhancement. We conclude that performance and training gains can be obtained from different strategical tES configurations, but more standardization, better translation between neurodevelopmental perspectives and tES principles, as well as pre-registered and controlled studies in critical populations are needed.