Clinical and cognitive effects of external trigeminal nerve stimulation (eTNS) in neurological and psychiatric disorders: a systematic review and meta-analysis.

This pre-registered (CRD42022322038) systematic review and meta-analysis investigated clinical and cognitive outcomes of external trigeminal nerve stimulation (eTNS) in neurological and psychiatric disorders. PubMed, OVID, Web of Science, Chinese National Knowledge Infrastructure, Wanfang, and VIP database for Chinese technical periodicals were searched (until 16/03/2022) to identify trials investigating cognitive and clinical outcomes of eTNS in neurological or psychiatric disorders. The Cochrane Risk of Bias 2.0 tool assessed randomized controlled trials (RCTs), while the Risk of Bias of Non-Randomized Studies (ROBINS-I) assessed single-arm trials. Fifty-five peer-reviewed articles based on 48 (27 RCTs; 21 single-arm) trials were included, of which 12 trials were meta-analyzed (N participants = 1048; of which ~3% ADHD, ~3% Epilepsy, ~94% Migraine; age range: 10-49 years). The meta-analyses showed that migraine pain intensity (K trials = 4, N = 485; SMD = 1.03, 95% CI[0.84-1.23]) and quality of life (K = 2, N = 304; SMD = 1.88, 95% CI[1.22-2.53]) significantly improved with eTNS combined with anti-migraine medication. Dimensional measures of depression improved with eTNS across 3 different disorders (K = 3, N = 111; SMD = 0.45, 95% CI[0.01-0.88]). eTNS was well-tolerated, with a good adverse event profile across disorders. eTNS is potentially clinically relevant in other disorders, but well-blinded, adequately powered RCTs must replicate findings and support optimal dosage guidance.

Computerized cognitive training in attention-deficit/hyperactivity disorder (ADHD): a meta-analysis of randomized controlled trials with blinded and objective outcomes.

This meta-analysis investigated the effects of computerized cognitive training (CCT) on clinical, neuropsychological and academic outcomes in individuals with attention-deficit/hyperactivity disorder (ADHD). The authors searched PubMed, Ovid, and Web of Science until 19th January 2022 for parallel-arm randomized controlled trials (RCTs) using CCT in individuals with ADHD. Random-effects meta-analyses pooled standardized mean differences (SMD) between CCT and comparator arms. RCT quality was assessed with the Cochrane Risk of Bias 2.0 tool (PROSPERO: CRD42021229279). Thirty-six RCTs were meta-analysed, 17 of which evaluated working memory training (WMT). Analysis of outcomes measured immediately post-treatment and judged to be "probably blinded" (PBLIND; trial n = 14) showed no effect on ADHD total (SMD = 0.12, 95%CI[-0.01 to -0.25]) or hyperactivity/impulsivity symptoms (SMD = 0.12, 95%[-0.03 to-0.28]). These findings remained when analyses were restricted to trials (n: 5-13) with children/adolescents, low medication exposure, semi-active controls, or WMT or multiple process training. There was a small improvement in inattention symptoms (SMD = 0.17, 95%CI[0.02-0.31]), which remained when trials were restricted to semi-active controls (SMD = 0.20, 95%CI[0.04-0.37]), and doubled in size when assessed in the intervention delivery setting (n = 5, SMD = 0.40, 95%CI[0.09-0.71]), suggesting a setting-specific effect. CCT improved WM (verbal: n = 15, SMD = 0.38, 95%CI[0.24-0.53]; visual-spatial: n = 9, SMD = 0.49, 95%CI[0.31-0.67]), but not other neuropsychological (e.g., attention, inhibition) or academic outcomes (e.g., reading, arithmetic; analysed n: 5-15). Longer-term improvement (at ~6-months) in verbal WM, reading comprehension, and ratings of executive functions were observed but relevant trials were limited in number (n: 5-7). There was no evidence that multi-process training was superior to working memory training. In sum, CCT led to shorter-term improvements in WM, with some evidence that verbal WM effects persisted in the longer-term. Clinical effects were limited to small, setting specific, short-term effects on inattention symptoms.

Effects of repetitive transcranial magnetic stimulation in children and young people with psychiatric disorders: a systematic review.

Repetitive transcranial magnetic stimulation (rTMS) has demonstrated benefits in adults with psychiatric disorders, but its clinical utility in children and young people (CYP) is unclear. This PRISMA systematic review used published and ongoing studies to examine the effects of rTMS on disorder-specific symptoms, mood and neurocognition in CYP with psychiatric disorders. We searched Medline via PubMed, Embase, PsychINFO via OVID, and Clinicaltrials.gov up to July 2023. Eligible studies involved multiple-session (i.e., treatment) rTMS in CYP (≤ 25 years-old) with psychiatric disorders. Two independent raters assessed the eligibility of studies and extracted data using a custom-built form. Out of 78 eligible studies (participant N = 1389), the majority (k = 54; 69%) reported an improvement in at least one outcome measure of disorder-specific core symptoms. Some studies (k = 21) examined rTMS effects on mood or neurocognition,: findings were largely positive. Overall, rTMS was well-tolerated with minimal side-effects. Of 17 ongoing or recently completed studies, many are sham-controlled RCTs with better blinding techniques and a larger estimated participant enrolment. Findings provide encouraging evidence for rTMS-related improvements in disorder-specific symptoms in CYP with different psychiatric disorders. However, in terms of both mood (for conditions other than depression) and neurocognitive outcomes, evidence is limited. Importantly, rTMS is well-tolerated and safe. Ongoing studies appear to be of improved methodological quality; however, future studies should broaden outcome measures to more comprehensively assess the effects of rTMS and develop guidance on dosage (i.e., treatment regimens).

Transcranial direct current stimulation (tDCS) combined with cognitive training in adolescent boys with ADHD: a double-blind, randomised, sham-controlled trial.

BACKGROUND: Transcranial direct current stimulation (tDCS) could be a side-effect-free alternative to psychostimulants in attention-deficit/hyperactivity disorder (ADHD). Although there is limited evidence for clinical and cognitive effects, most studies were small, single-session and stimulated left dorsolateral prefrontal cortex (dlPFC). No sham-controlled study has stimulated the right inferior frontal cortex (rIFC), which is the most consistently under-functioning region in ADHD, with multiple anodal-tDCS sessions combined with cognitive training (CT) to enhance effects. Thus, we investigated the clinical and cognitive effects of multi-session anodal-tDCS over rIFC combined with CT in double-blind, randomised, sham-controlled trial (RCT, ISRCTN48265228). METHODS: Fifty boys with ADHD (10-18 years) received 15 weekday sessions of anodal- or sham-tDCS over rIFC combined with CT (20 min, 1 mA). ANCOVA, adjusting for baseline measures, age and medication status, tested group differences in clinical and ADHD-relevant executive functions at posttreatment and after 6 months. RESULTS: ADHD-Rating Scale, Conners ADHD Index and adverse effects were significantly lower at post-treatment after sham relative to anodal tDCS. No other effects were significant. CONCLUSIONS: This rigorous and largest RCT of tDCS in adolescent boys with ADHD found no evidence of improved ADHD symptoms or cognitive performance following multi-session anodal tDCS over rIFC combined with CT. These findings extend limited meta-analytic evidence of cognitive and clinical effects in ADHD after 1-5 tDCS sessions over mainly left dlPFC. Given that tDCS is commercially and clinically available, the findings are important as they suggest that rIFC stimulation may not be indicated as a neurotherapy for cognitive or clinical remediation for ADHD.

Effects of transcranial direct current stimulation in children and young people with psychiatric disorders: a systematic review.

Transcranial direct current stimulation (tDCS) has demonstrated benefits in adults with various psychiatric disorders, but its clinical utility in children and young people (CYP) remains unclear. This PRISMA systematic review used published and ongoing studies to examine the effects of tDCS on disorder-specific symptoms, mood and neurocognition in CYP with psychiatric disorders. We searched Medline via PubMed, Embase, PsychINFO via OVID, and Clinicaltrials.gov up to December 2022. Eligible studies involved multiple session (i.e., treatment) tDCS in CYP (≤ 25 years old) with psychiatric disorders. Two independent raters assessed the eligibility of studies and extracted data using a custom-built form. Of 33 eligible studies (participant N = 517), the majority (n = 27) reported an improvement in at least one outcome measure of disorder-specific symptoms. Few studies (n = 13) examined tDCS effects on mood and/or neurocognition, but findings were mainly positive. Overall, tDCS was well tolerated with minimal side effects. Of 11 eligible ongoing studies, many are sham-controlled RCTs (n = 9) with better blinding techniques and a larger estimated participant enrolment (M = 79.7; range 15-172) than published studies. Although encouraging, the evidence to date is insufficient to firmly conclude that tDCS can improve clinical symptoms, mood, or cognition in CYP with psychiatric disorders. Ongoing studies appear of improved methodological quality; however, future studies should broaden outcome measures to more comprehensively assess the effects of tDCS and develop dosage guidance (i.e., treatment regimens).

Noninvasive brain stimulation in children and adults with attention-deficit/hyperactivity disorder: a systematic review and meta-analysis.

BACKGROUND: Repetitive transcranial magnetic stimulation (rTMS) or transcranial direct current stimulation (tDCS) could provide treatment alternatives to stimulant medication for attention-deficit/hyperactivity disorder (ADHD), given some evidence for improvements in cognition and clinical symptoms. However, despite a lack of solid evidence for their use, rTMS and tDCS are already offered clinically and commercially in ADHD. This systematic review and meta-analysis aimed to critically appraise rTMS and tDCS studies in ADHD to inform good research and clinical practice. METHODS: A systematic search (up to February 2019) identified 18 studies (rTMS 4, tDCS 14; 311 children and adults with ADHD) stimulating mainly the dorsolateral prefrontal cortex (dlPFC). We included 12 anodal tDCS studies (232 children and adults with ADHD) in 3 random-effects meta-analyses of cognitive measures of attention, inhibition and processing speed. RESULTS: The review of rTMS and tDCS showed positive effects in some functions but not others, and little evidence for clinical improvement. The meta-analyses of 1 to 5 sessions of anodal tDCS over mainly the left or bilateral dlPFC showed trend-level improvements in inhibition and processing speed, but not in attention. LIMITATIONS: Heterogeneity in stimulation parameters, patient age and outcome measures limited the interpretation of findings. CONCLUSION: The review and meta-analysis showed limited evidence that 1 to 5 sessions of rTMS and tDCS, mostly of the dlPFC, improved clinical or cognitive measures of ADHD. These findings did not support using rTMS or tDCS of the dlPFC as an alternative neurotherapy for ADHD as yet. Larger, multi-session stimulation studies identifying more optimal sites and stimulation parameters in combination with cognitive training could achieve larger effects.

Association between alexithymia and non-suicidal self-injury in psychiatric patients: the mediating role of self-esteem and the moderating role of emotional intelligence.

BACKGROUND: Raffagnato's theory claims that if people have no words to express their emotions (alexithymia), they express themselves by venting or through non-suicidal self-injury (NSSI). However, these associations have not been confirmed in psychiatric patients. This study explored the relationship between alexithymia and NSSI in psychiatric patients and the potential underlying psychological mechanisms. METHODS: This retrospective study involved face-to-face interviews with 449 outpatients consecutively recruited from West China Hospital. Alexithymia, self-esteem, NSSI, and emotional intelligence (EI) were measured. The moderating role of EI and the mediating role of self-esteem between alexithymia and NSSI were also explored. Logistic regressions were used to examine whether sociodemographic, clinical variables and alexithymia were independently associated with NSSI. RESULTS: The DSM-5 NSSI disorder and alexithymia prevalences were found to be 32.5% and 45.2%. When the other covariables were controlled for, the alexithymic patients were found to be at increased odds (OR 2.76) of engaging in NSSI behaviors. These results confirmed the strong associations between alexithymia, low self-esteem, and NSSI risk. Lower EI was found to be related to the connections between alexithymia and NSSI. Except for the lower risk in anxiety patients, the risk of NSSI was similar for patients with other mental disorders, CONCLUSION: This study revealed the psychological mechanisms through which alexithymia increases the risk of NSSI. Therefore, to reduce NSSI risk, screening for alexithymia should be emphasized. Self-esteem as a targeted psychological intervention could also assist in mitigating the process from alexithymia to NSSI behaviors, and EI training for psychiatric patients could weaken the relationship between alexithymia and NSSI.

Are Small Effects the Indispensable Foundation for a Cumulative Psychological Science? A Reply to Götz et al. (2022).

In the January 2022 issue of Perspectives, Götz et al. argued that small effects are "the indispensable foundation for a cumulative psychological science." They supported their argument by claiming that (a) psychology, like genetics, consists of complex phenomena explained by additive small effects; (b) psychological-research culture rewards large effects, which means small effects are being ignored; and (c) small effects become meaningful at scale and over time. We rebut these claims with three objections: First, the analogy between genetics and psychology is misleading; second, p values are the main currency for publication in psychology, meaning that any biases in the literature are (currently) caused by pressure to publish statistically significant results and not large effects; and third, claims regarding small effects as important and consequential must be supported by empirical evidence or, at least, a falsifiable line of reasoning. If accepted uncritically, we believe the arguments of Götz et al. could be used as a blanket justification for the importance of any and all "small" effects, thereby undermining best practices in effect-size interpretation. We end with guidance on evaluating effect sizes in relative, not absolute, terms.

Teaching open and reproducible scholarship: a critical review of the evidence base for current pedagogical methods and their outcomes.

In recent years, the scientific community has called for improvements in the credibility, robustness and reproducibility of research, characterized by increased interest and promotion of open and transparent research practices. While progress has been positive, there is a lack of consideration about how this approach can be embedded into undergraduate and postgraduate research training. Specifically, a critical overview of the literature which investigates how integrating open and reproducible science may influence student outcomes is needed. In this paper, we provide the first critical review of literature surrounding the integration of open and reproducible scholarship into teaching and learning and its associated outcomes in students. Our review highlighted how embedding open and reproducible scholarship appears to be associated with (i) students' scientific literacies (i.e. students' understanding of open research, consumption of science and the development of transferable skills); (ii) student engagement (i.e. motivation and engagement with learning, collaboration and engagement in open research) and (iii) students' attitudes towards science (i.e. trust in science and confidence in research findings). However, our review also identified a need for more robust and rigorous methods within pedagogical research, including more interventional and experimental evaluations of teaching practice. We discuss implications for teaching and learning scholarship.

A reproducible systematic map of research on the illusory truth effect.

People believe information more if they have encountered it before, a finding known as the illusory truth effect. But what is the evidence for the generality and pervasiveness of the illusory truth effect? Our preregistered systematic map describes the existing knowledge base and objectively assesses the quality, completeness and interpretability of the evidence provided by empirical studies in the literature. A systematic search of 16 bibliographic and grey literature databases identified 93 reports with a total of 181 eligible studies. All studies were conducted at Western universities, and most used convenience samples. Most studies used verbatim repetition of trivia statements in a single testing session with a minimal delay between exposure and test. The exposure tasks, filler tasks and truth measures varied substantially across studies, with no standardisation of materials or procedures. Many reports lacked transparency, both in terms of open science practices and reporting of descriptive statistics and exclusions. Systematic mapping resulted in a searchable database of illusory truth effect studies ( https://osf.io/37xma/ ). Key limitations of the current literature include the need for greater diversity of materials as stimuli (e.g., political or health contents), more participants from non-Western countries, studies examining effects of multiple repetitions and longer intersession intervals, and closer examination of the dependency of effects on the choice of exposure task and truth measure. These gaps could be investigated using carefully designed multi-lab studies. With a lack of external replications, preregistrations, data and code, verifying replicability and robustness is only possible for a small number of studies.

What senior academics can do to support reproducible and open research: a short, three-step guide.

Increasingly, policies are being introduced to reward and recognise open research practices, while the adoption of such practices into research routines is being facilitated by many grassroots initiatives. However, despite this widespread endorsement and support, as well as various efforts led by early career researchers, open research is yet to be widely adopted. For open research to become the norm, initiatives should engage academics from all career stages, particularly senior academics (namely senior lecturers, readers, professors) given their routine involvement in determining the quality of research. Senior academics, however, face unique challenges in implementing policy changes and supporting grassroots initiatives. Given that-like all researchers-senior academics are motivated by self-interest, this paper lays out three feasible steps that senior academics can take to improve the quality and productivity of their research, that also serve to engender open research. These steps include changing (a) hiring criteria, (b) how scholarly outputs are credited, and (c) how we fund and publish in line with open research principles. The guidance we provide is accompanied by material for further reading.

Towards a culture of open scholarship: the role of pedagogical communities.

The UK House of Commons Science and Technology Committee has called for evidence on the roles that different stakeholders play in reproducibility and research integrity. Of central priority are proposals for improving research integrity and quality, as well as guidance and support for researchers. In response to this, we argue that there is one important component of research integrity that is often absent from discussion: the pedagogical consequences of how we teach, mentor, and supervise students through open scholarship. We justify the need to integrate open scholarship principles into research training within higher education and argue that pedagogical communities play a key role in fostering an inclusive culture of open scholarship. We illustrate these benefits by presenting the Framework for Open and Reproducible Research Training (FORRT), an international grassroots community whose goal is to provide support, resources, visibility, and advocacy for the adoption of principled, open teaching and mentoring practices, whilst generating conversations about the ethics and social impact of higher-education pedagogy. Representing a diverse group of early-career researchers and students across specialisms, we advocate for greater recognition of and support for pedagogical communities, and encourage all research stakeholders to engage with these communities to enable long-term, sustainable change.

The effect of transcranial direct current stimulation (tDCS) combined with cognitive training on EEG spectral power in adolescent boys with ADHD: A double-blind, randomized, sham-controlled trial.

Transcranial direct current stimulation (tDCS) is a possible alternative to psychostimulants in Attention-Deficit/Hyperactivity Disorder (ADHD), but its mechanisms of action in children and adolescents with ADHD are poorly understood. We conducted the first 15-session, sham-controlled study of anodal tDCS over right inferior frontal cortex (rIFC) combined with cognitive training (CT) in 50 children/adolescents with ADHD. We investigated the mechanisms of action on resting and Go/No-Go Task-based QEEG measures in a subgroup of 23 participants with ADHD (n, sham = 10; anodal tDCS = 13). We failed to find a significant sham versus anodal tDCS group differences in QEEG spectral power during rest and Go/No-Go Task performance, a correlation between QEEG and Go/No-Go Task performance, and changes in clinical and cognitive measures. These findings extend the non-significant clinical and cognitive effects in our sample of 50 children/adolescents with ADHD. Given that the subgroup of 23 participants would have been underpowered, the interpretation of our findings is limited and should be used as a foundation for future investigations. Larger, adequately powered randomized controlled trials should explore different protocols titrated to the individual and using comprehensive measures to assess cognitive, clinical, and neural effects of tDCS and its underlying mechanisms of action in ADHD.

Systematic Review and Meta-analysis: Screening Tools for Attention-Deficit/Hyperactivity Disorder in Children and Adolescents.

OBJECTIVE: This systematic review and meta-analysis aimed to determine the accuracies of a broad range of screening tools for attention-deficit/hyperactivity disorder (ADHD) in children and adolescents, and to compare the diagnostic accuracy of tools between population-based and clinical/high-risk samples, and across reporters. METHOD: MEDLINE, PsycINFO, EMBASE, and PubMed were searched up until February 20, 2020, with no language restrictions. Studies reporting diagnostic accuracy of a screening tool against a diagnosis of ADHD in children and adolescents <18 years of age were eligible for inclusion. Meta-analyses were undertaken to provide pooled estimates of the area under the curve (AUC), and sensitivity and specificity of groups of measures. RESULTS: A total of 75 studies published between 1985 and 2021 reporting on 41 screening tools that were grouped into 4 categories (Achenbach System of Empirically Based Assessment [ASEBA], DSM-IV symptom scales, SDQ, and Other Scales) were retained. The pooled AUC for studies using a combined ADHD symptoms score was 0.82 (95% CI = 0.78-0.86), although this varied considerably across reporters (0.67-0.92) and populations (CI = 0.60-0.95). None of the measures met minimal standards for acceptable sensitivity (0.8) and specificity (0.8). CONCLUSION: Most tools have excellent overall diagnostic accuracy as indicated by the AUC. However, a single measure completed by a single reporter is unlikely to have sufficient sensitivity and specificity for clinical use or population screening.

Double-Blind, Sham-Controlled Randomized Trial Testing the Efficacy of fMRI Neurofeedback on Clinical and Cognitive Measures in Children With ADHD.

OBJECTIVE: Functional MRI neurofeedback (fMRI-NF) could potentially be a novel, safe nonpharmacological treatment for attention deficit hyperactivity disorder (ADHD). A proof-of-concept randomized controlled trial of fMRI-NF of the right inferior frontal cortex (rIFC), compared to an active control condition, showed promising improvement of ADHD symptoms (albeit in both groups) and in brain function. However, comparison with a placebo condition in a larger trial is required to test efficacy. METHODS: This double-blind, sham-controlled randomized controlled trial tested the effectiveness and efficacy of fMRI-NF of the rIFC on symptoms and executive functions in 88 boys with ADHD (44 each in the active and sham arms). To investigate treatment-related changes, groups were compared at the posttreatment and 6-month follow-up assessments, controlling for baseline scores, age, and medication status. The primary outcome measure was posttreatment score on the ADHD Rating Scale (ADHD-RS). RESULTS: No significant group differences were found on the ADHD-RS. Both groups showed similar decreases in other clinical and cognitive measures, except for a significantly greater decrease in irritability and improvement in motor inhibition in sham relative to active fMRI-NF at the posttreatment assessment, covarying for baseline. There were no significant side effects or adverse events. The active relative to the sham fMRI-NF group showed enhanced activation in rIFC and other frontal and temporo-occipital-cerebellar self-regulation areas. However, there was no progressive rIFC upregulation, correlation with ADHD-RS scores, or transfer of learning. CONCLUSIONS: Contrary to the hypothesis, the study findings do not suggest that fMRI-NF of the rIFC is effective in improving clinical symptoms or cognition in boys with ADHD.

Null Effects on Working Memory and Verbal Fluency Tasks When Applying Anodal tDCS to the Inferior Frontal Gyrus of Healthy Participants.

Transcranial direct current stimulation (tDCS) is a technique used to modify cognition by modulating underlying cortical excitability via weak electric current applied through the scalp. Although many studies have reported positive effects with tDCS, a number of recent studies highlight that tDCS effects can be small and difficult to reproduce. This is especially the case when attempting to modulate performance using single applications of tDCS in healthy participants. Possible reasons may be that optimal stimulation parameters have yet to be identified, and that individual variation in cortical activity and/or level of ability confound outcomes. To address these points, we carried out a series of experiments in which we attempted to modulate performance in fluency and working memory probe tasks using stimulation parameters which have been associated with positive outcomes: we targeted the left inferior frontal gyrus (LIFG) and compared performance when applying a 1.5 mA anodal current for 25 min and with sham stimulation. There is evidence that LIFG plays a role in these tasks and previous studies have found positive effects of stimulation. We also compared our experimental group (N = 19-20) with a control group receiving no stimulation (n = 24). More importantly, we also considered effects on subgroups subdivided according to memory span as well as to more direct measures of executive function abilities and motivational levels. We found no systematic effect of stimulation. Our findings are in line with a growing body of evidence that tDCS produces unreliable effects. We acknowledge that our findings speak to the conditions we investigated, and that alternative protocols (e.g., multiple sessions, clinical samples, and different stimulation polarities) may be more effective. We encourage further research to explore optimal conditions for tDCS efficacy, given the potential benefits that this technique poses for understanding and enhancing cognition.

Transcranial direct current stimulation (tDCS) modulation of picture naming and word reading: A meta-analysis of single session tDCS applied to healthy participants.

Recent reviews quantifying the effects of single sessions of transcranial direct current stimulation (or tDCS) in healthy volunteers find only minor effects on cognition despite the popularity of this technique. Here, we wanted to quantify the effects of tDCS on language production tasks that measure word reading and picture naming. We reviewed 14 papers measuring tDCS effects across a total of 96 conditions to a) quantify effects of conventional stimulation on language regions (i.e., left hemisphere anodal tDCS administered to temporal/frontal areas) under normal conditions or under conditions of cognitive (semantic) interference; b) identify parameters which may moderate the size of the tDCS effect within conventional stimulation protocols (e.g., online vs offline, high vs. low current densities, and short vs. long durations), as well as within types of stimulation not typically explored by previous reviews (i.e., right hemisphere anodal tDCS or left/right hemisphere cathodal tDCS). In all analyses there was no significant effect of tDCS, but we did find a small but significant effect of time and duration of stimulation with stronger effects for offline stimulation and for shorter durations (< 15min). We also found some indication of publication bias towards reporting positive effects. We encourage further experimentation in order resolve the disparity between the current popularity of tDCS and its poor efficacy in healthy participants.

Limits to tDCS effects in language: Failures to modulate word production in healthy participants with frontal or temporal tDCS.

Transcranial direct current stimulation (tDCS) is a method of non-invasive brain stimulation widely used to modulate cognitive functions. Recent studies, however, suggests that effects are unreliable, small and often non-significant at least when stimulation is applied in a single session to healthy individuals. We examined the effects of frontal and temporal lobe anodal tDCS on naming and reading tasks and considered possible interactions with linguistic activation and selection mechanisms as well as possible interactions with item difficulty and participant individual variability. Across four separate experiments (N, Exp 1A = 18; 1B = 20; 1C = 18; 2 = 17), we failed to find any difference between real and sham stimulation. Moreover, we found no evidence of significant effects limited to particular conditions (i.e., those requiring suppression of semantic interference), to a subset of participants or to longer RTs. Our findings sound a cautionary note on using tDCS as a means to modulate cognitive performance. Consistent effects of tDCS may be difficult to demonstrate in healthy participants in reading and naming tasks, and be limited to cases of pathological neurophysiology and/or to the use of learning paradigms.