Enhancement of selective attention by tDCS: Interaction with interference in a Sternberg task

Towards optimized methodological parameters for maximizing the behavioral effects of transcranial direct current stimulation

Introduction

Transcranial direct current stimulation (tDCS) administers low-intensity direct current electrical stimulation to brain regions via electrodes arranged on the surface of the scalp. The core promise of tDCS is its ability to modulate brain activity and affect performance on diverse cognitive functions (affording causal inferences regarding regional brain activity and behavior), but the optimal methodological parameters for maximizing behavioral effects remain to be elucidated. Here we sought to examine the effects of 10 stimulation and experimental design factors across a series of five cognitive domains: motor performance, visual search, working memory, vigilance, and response inhibition. The objective was to identify a set of optimal parameter settings that consistently and reliably maximized the behavioral effects of tDCS within each cognitive domain.

Methods

We surveyed tDCS effects on these various cognitive functions in healthy young adults, ultimately resulting in 721 effects across 106 published reports. Hierarchical Bayesian meta-regression models were fit to characterize how (and to what extent) these design parameters differentially predict the likelihood of positive/negative behavioral outcomes.

Results

Consistent with many previous meta-analyses of tDCS effects, extensive variability was observed across tasks and measured outcomes. Consequently, most design parameters did not confer consistent advantages or disadvantages to behavioral effects-a domain-general model suggested an advantage to using within-subjects designs (versus between-subjects) and the tendency for cathodal stimulation (relative to anodal stimulation) to produce reduced behavioral effects, but these associations were scarcely-evident in domain-specific models.

Discussion

These findings highlight the urgent need for tDCS studies to more systematically probe the effects of these parameters on behavior to fulfill the promise of identifying causal links between brain function and cognition.

Different montages of transcranial direct current stimulation on postural stability in chronic low back pain patients: A randomized sham-controlled study

BACKGROUND

Impairment in both the motor and cognitive aspects of postural control is a critical issue in patients with chronic low back pain (CLBP) who experience high pain anxiety (HPA).

OBJECTIVE

This study aimed to compare the effects of cathodal and anodal transcranial direct current stimulation (c-tDCS and a-tDCS) over the dorsolateral prefrontal cortex (DLPFC) on postural control during cognitive postural tasks in CLBP patients with HPA.

METHODS

This study included 66 patients randomly assigned to three groups: DLPFC a-tDCS, DLPFC c-tDCS, and sham tDCS. All groups received 20 minutes of tDCS, but the stimulation was gradually turned off in the sham group. Postural stability indices were assessed using the Biodex Balance System.

RESULTS

Both the a-tDCS and c-tDCS groups showed a significant reduction in most postural stability indices at static and dynamic levels after the interventions (immediately, 24 hours, and one-week follow-up) during the cognitive postural task (P< 0.01). Additionally, there was a significant improvement in postural balance in the a-tDCS and c-tDCS groups compared to the sham tDCS group (P< 0.01). Furthermore, the a-tDCS group showed significantly greater improvement than the c-tDCS group (P< 0.01).

CONCLUSION

Based on the results, both a-tDCS and c-tDCS over the DLPFC had positive effects on postural control during cognitive postural tasks in CLBP patients with HPA.

Acute effect of transcranial direct current stimulation (tDCS) on postural control of trained athletes: A randomized controlled trial

Transcranial direct current stimulation (tDCS) is used to modulate brain function, and can modulate motor and postural control. While the acute effect of tDCS is well documented on patients, little is still known whether tDCS can alter the motor control of healthy trained participants. This study aimed to assess the acute effect of tDCS on postural control of parkour practitioners, known for their good balance abilities and their neuromuscular specificities that make them good candidates for tDCS intervention. Eighteen parkour practitioners were tested on three occasions in the laboratory for each stimulation condition (2 mA; 20 minutes)-primary motor cortex (M1), dorsolateral prefrontal cortex (dlPFC) and sham (placebo). Postural control was evaluated PRE and POST each stimulation by measuring Center of Pressure (CoP) displacements on a force platform during static conditions (bipedal and unipedal stance). Following M1 stimulation, significant decreases were observed in CoP area in unipedal (from 607.1 ± 297.9 mm2 to 451.1 ± 173.9 mm2, P = 0.003) and bipedal (from 157.5 ± 74.1 mm2 to 117.6 ± 59.8 mm2 P<0.001) stances. As well, the CoP total length was significantly reduced in bipedal (from 3416.8 ± 295.4 mm to 3280.6 ± 306.2 mm, P = 0.005) as well as in unipedal stance (from 4259.6 ± 398.4 mm to 3846.5 ± 468.9 mm, P<0.001), only after M1 stimulation. Relative pre-post changes observed after M1 stimulation were negatively correlated to experience in parkour only after unipedal stance (r = 0.715, P<0.001), meaning that the more participants were trained the less tDCS was effective. No significant changes were noticed after sham and dlPFC stimulation. These results suggested that the modulation of gait performance in athletes following an acute intervention of tDCS is specific to the targeted brain region, and that postures with reduced base of support (such as unipedal stance) were more sensitive to tDCS.

Cathodal HD-tDCS and attention: A study on patients with intractable left lateral frontal lobe epilepsy

OBJECTIVE

Defects in the attentional network in patients with epilepsy are influenced by factors such as the location of epileptic foci. Examining the impact of cathodal high-definition transcranial direct current stimulation (HD-tDCS) on attention components could provide insights into potential attention-related side effects of tDCS. This study aimed to investigate the effect of cathodal HD-tDCS on interictal epileptiform discharges (IEDs), auditory/visual (A/V) attention components, and reaction time (RT) in patients with intractable focal left lateral frontal lobe epilepsy (LFLE).

METHODS

To control for variations in individual epilepsy syndrome, 12 adult participants diagnosed with drug-resistant left LFLE with focal cortical IEDs on C3 underwent repeated measurements at pretest, posttest, and follow-up steps. 4 × 1 ring electrodes (cathode on C3 and four anodes on F3, P3, T3, and Cz) delivered 2 mA DC for 20 min per session for 10 consecutive days. The integrated visual and auditory continuous performance test (IVA+) assessed the A/V attention components and RT. One-way repeated-measure ANOVA was used.

RESULTS

The findings suggest a significant effect in reducing IEDs. The IVA+ results showed a significant improvement in auditory divided attention and visual selective and focused attention (p < 0.05). In the follow-up, these changes demonstrated lasting efficacy. A/V speed scales increased (p < 0.05), showing a significant decrease in reaction time.

CONCLUSIONS

Cathodal HD-tDCS significantly reduced IEDs and improved the components of auditory divided attention, visual focused attention, and visual selective attention, with a reduction in patient reaction time. A significant lasting, side-effect-free positive effect was observed for up to one month after the intervention.

Transcranial direct current stimulation over dorsolateral prefrontal cortex improves postural stability in non-specific chronic low back pain patients with high fear of pain: A randomized sham-controlled trial

Deficits in postural stability in response to environmental challenges are seen in chronic low back pain (CLBP) patients with high fear of pain (HFP). Hence, it is essential to follow effective approaches to treat postural stability deficits and improve the health status of these patients. The current study aimed to compare the effects of cathodal and anodal transcranial direct current stimulation (c-tDCS and a-tDCS) over the left dorsolateral prefrontal cortex (DLPFC) on postural stability in non-specific CLBP patients with HFP. In this randomized clinical trial study, 75 patients were randomly assigned to left DLPFC a-tDCS, left DLPFC c-tDCS and sham stimulation groups (n = 25 in each group). All groups received a single-session 2 mA tDCS for 20 min, but the stimulation was slowly turned off after 30 s in the sham group. Before, immediately, 24 h and 1 week after the interventions, postural stability indices were assessed using a Biodex Balance System. A significant reduction in most indices was shown in both a-tDCS and c-tDCS groups after interventions (immediately, 24 h and 1 week follow-up) during static and dynamic postural tasks compared with the sham tDCS group (p < .01). In addition, some tests showed a significant difference between a-tDCS and c-tDCS (p < .05). The findings indicated positive effects of both a-tDCS and c-tDCS on the left DLPFC, with more efficacy of a-tDCS on postural stability in LBP patients with HFP.

Modulation of resting-state networks following repetitive transcranial alternating current stimulation of the dorsolateral prefrontal cortex

Transcranial alternating current stimulation (tACS) offers a unique method to temporarily manipulate the activity of the stimulated brain region in a frequency-dependent manner. However, it is not clear if repetitive modulation of ongoing oscillatory activity with tACS over multiple days can induce changes in grey matter resting-state functional connectivity and white matter structural integrity. The current study addresses this question by applying multiple-session theta band stimulation on the left dorsolateral prefrontal cortex (L-DLPFC) during arithmetic training. Fifty healthy participants (25 males and 25 females) were randomly assigned to the experimental and sham groups, half of the participants received individually adjusted theta band tACS, and half received sham stimulation. Resting-state functional magnetic resonance (rs-fMRI) and diffusion-weighted imaging (DWI) data were collected before and after 3 days of tACS-supported procedural learning training. Resting-state network analysis showed a significant increase in connectivity for the frontoparietal network (FPN) with the precuneus cortex. Seed-based analysis with a seed defined at the primary stimulation site showed an increase in connectivity with the precuneus cortex, posterior cingulate cortex (PCC), and lateral occipital cortex. There were no effects on the structural integrity of white matter tracts as measured by fractional anisotropy, and on behavioral measures. In conclusion, the study suggests that multi-session task-associated tACS can produce significant changes in resting-state functional connectivity; however, changes in functional connectivity do not necessarily translate to changes in white matter structure or behavioral performance.

Neural Mechanism Underlying Task-Specific Enhancement of Motor Learning by Concurrent Transcranial Direct Current Stimulation

The optimal protocol for neuromodulation by transcranial direct current stimulation (tDCS) remains unclear. Using the rotarod paradigm, we found that mouse motor learning was enhanced by anodal tDCS (3.2 mA/cm2) during but not before or after the performance of a task. Dual-task experiments showed that motor learning enhancement was specific to the task accompanied by anodal tDCS. Studies using a mouse model of stroke induced by middle cerebral artery occlusion showed that concurrent anodal tDCS restored motor learning capability in a task-specific manner. Transcranial in vivo Ca2+ imaging further showed that anodal tDCS elevated and cathodal tDCS suppressed neuronal activity in the primary motor cortex (M1). Anodal tDCS specifically promoted the activity of task-related M1 neurons during task performance, suggesting that elevated Hebbian synaptic potentiation in task-activated circuits accounts for the motor learning enhancement. Thus, application of tDCS concurrent with the targeted behavioral dysfunction could be an effective approach to treating brain disorders.

Testing the Reproducibility of the Effects of Transcranial Direct Current Stimulation: Failure to Modulate Beauty Perception by Brain Stimulation

Transcranial direct current stimulation (tDCS) has been recognized as a promising tool for investigating the causal relationship between specific brain areas of interest and behavior. However, the reproducibility of previous tDCS studies is often questioned because of failures in replication. This study focused on the effects of tDCS on one cognitive domain: beauty perception. To date, the modulation of beauty perception by tDCS has been shown in two studies: Cattaneo et al. (2014) and Nakamura and Kawabata (2015). Here, we aimed at replicating their studies and investigating the effects of tDCS on beauty perception using the following parameters: (1) cathodal stimulation over the medial prefrontal cortex (mPFC) (Nakamura and Kawabata, 2015); (2) anodal stimulation over the left dorsolateral prefrontal cortex (lDLPFC) (Cattaneo et al., 2014). We also performed a more focal stimulation targeting the orbitofrontal cortex (OFC) to determine the optimal stimulation site for modulating beauty perception (3). Participants rated the subjectively-perceived beauty of the images before and after the tDCS administration. We divided images into four clusters according to the obtained scores in our preliminary study and examined changes in beauty ratings in each image cluster separately to exclude factors, such as stimuli attributions that may reduce tDCS effects. The results showed no strong effects of tDCS with the same parameters as in previous studies on beauty rating scores in any image cluster. Likewise, anodal stimulation over the OFC did not result in a change in rating scores. In contrast to previous studies, the current study did not corroborate the effects of tDCS on beauty perception. Our findings provide evidence regarding the recent reproducibility issue of tDCS effects and suggest the possible inflation of its effects on cognitive domains.

Impact of Psychosocial Occupational Therapy Combined with Anodal Transcranial Direct Current Stimulation to the Left Dorsolateral Prefrontal Cortex on the Cognitive Performance of Patients with Schizophrenia: A Randomized Controlled Trial

Background

The most common cognitive dysfunctions in patients with schizophrenia are information processing, memory, and learning. Based on the hypothesis of rehabilitation and brain stimulation in memory and learning, adding a form of neuromodulation to conventional rehabilitation might increase the effectiveness of treatments.

Aims

To explore the effects of psychosocial occupational therapy combined with anodal Transcranial Direct Current Stimulation (tDCS) on cognitive performance in patients with Schizophrenia.

Methods

Twenty-four patients diagnosed with schizophrenia were randomized into the experimental and control groups. We used The Cambridge Neuropsychological Test Automated Battery (CANTAB) and the Loewenstein Occupational Therapy Cognitive Assessment battery (LOTCA) to assess spatial recognition, attention, visual memory, learning abilities, and high-level cognitive functions like problem-solving. All participants received customized psychosocial occupational therapy activities. Furthermore, the experimental group received 12 sessions of active anodal tDCS for 20 minutes with 2 mA intensity on the left dorsolateral prefrontal cortex (DLPFC) while the patients in the sham group received sham tDCS.

Results

Combining tDCS to conventional psychosocial occupational therapy resulted in a significant increase in spatial memory, visual learning, and attention.

Conclusions

Anodal tDCS on the left DLPFC improved visual memory, attention, and learning abilities. Contrary to our expectations, we could not find any changes in complex and more demanding cognitive functions.

Motor stroke recovery after tDCS: a systematic review

The purpose of the present study was to investigate the effects of transcranial direct current stimulation (tDCS) on motor recovery in adult patients with stroke, taking into account the parameters that could influence the motor recovery responses. The second aim was to identify the best tDCS parameters and recommendations available based on the enhanced motor recovery demonstrated by the analyzed studies. Our systematic review was performed by searching full-text articles published before February 18, 2019 in the PubMed database. Different methods of applying tDCS in association with several complementary therapies were identified. Studies investigating the motor recovery effects of tDCS in adult patients with stroke were considered. Studies investigating different neurologic conditions and psychiatric disorders or those not meeting our methodologic criteria were excluded. The main parameters and outcomes of tDCS treatments are reported. There is not a robust concordance among the study outcomes with regard to the enhancement of motor recovery associated with the clinical application of tDCS. This is mainly due to the heterogeneity of clinical data, tDCS approaches, combined interventions, and outcome measurements. tDCS could be an effective approach to promote adaptive plasticity in the stroke population with significant positive premotor and postmotor rehabilitation effects. Future studies with larger sample sizes and high-quality studies with a better standardization of stimulation protocols are needed to improve the study quality, further corroborate our results, and identify the optimal tDCS protocols.

Using transcranial direct current stimulation (tDCS) on the dorsolateral prefrontal cortex to promote long-term foreign language vocabulary learning

Transcranial direct current stimulation (tDCS) on the dorsolateral prefrontal cortex (DLPFC) was used to improve foreign-langue learning while using mental imagery. Participants underwent two sessions of 1 mA, 1.5 mA, or sham stimulation prior to learning Swahili-English word pairs two consecutive days. During learning, participants were encouraged to create a mental image of the associated English word. Twenty-four hours after learning and one week later, participants received a cued recall test. A linear dose-response effect of stimulation was found across both tests that occurred long after the immediate effects of stimulation. Follow-up comparisons revealed that only the 1.5 mA condition differed from the sham group. Exploratory moderating effects revealed interactions with sleep quality and handedness. Those with poorer sleep and who were left-handed showed greater recall after 1.5 mA of stimulation than those with better sleep and right-handers. A follow-up behavioral study probing strategy usage indicated that mental imagery strategy use did not strongly impact learning but point to other possible mechanisms including the importance of attending to multimodal perceptual details and memory consolidation. This preliminary evidence supports the role of the DLPFC or connected regions in foreign language vocabulary learning and verbal memory encoding.

Identifying regions in prefrontal cortex related to working memory improvement: A novel meta-analytic method using electric field modeling

Altering cortical activity using transcranial direct current stimulation (tDCS) has been shown to improve working memory (WM) performance. Due to large inter-experimental variability in the tDCS montage configuration and strength of induced electric fields, results have been mixed. Here, we present a novel meta-analytic method relating behavioral effect sizes to electric field strength to identify brain regions underlying largest tDCS-induced WM improvement. Simulations on 69 studies targeting left prefrontal cortex showed that tDCS electric field strength in lower dorsolateral prefrontal cortex (Brodmann area 45/47) relates most strongly to improved WM performance. This region explained 7.8 % of variance, equaling a medium effect. A similar region was identified when correlating WM performance and electric field strength of right prefrontal tDCS studies (n = 18). Maximum electric field strength of five previously used tDCS configurations were outside of this location. We thus propose a new tDCS montage which maximizes the tDCS electric field strength in that brain region. Our findings can benefit future tDCS studies that aim to affect WM function.

tDCS randomized controlled trials in no-structural diseases: a quantitative review

The increasing number and quality of randomized controlled trials (RCTs) employing transcranial direct current stimulation (tDCS) denote the rising awareness of neuroscientific community about its electroceutical potential and opening to include these treatments in the framework of medical therapies under the indications of the international authorities. The purpose of this quantitative review is to estimate the recommendation strength applying the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) criteria and PICO (population, intervention, comparison, outcome) model values for effective tDCS treatments on no-structural diseases, and to provide an estimate of Sham effect for future RCTs. Applying GRADE evaluation pathway, we searched in literature the tDCS-based RCTs in psychophysical diseases displaying a major involvement of brain electrical activity imbalances. Three independent authors agreed on Class 1 RCTs (18 studies) and meta-analyses were carried out using a random-effects model for pathologies sub-selected based on PICO and systemic involvement criteria. The meta-analysis integrated with extensive evidence of negligible side effects and low-cost, easy-to-use procedures, indicated that tDCS treatments for depression and fatigue in Multiple Sclerosis ranked between moderately and highly recommendable. For these interventions we reported the PICO variables, with left vs. right dorsolateral prefrontal target for 30 min/10 days against depression and bilateral somatosensory vs occipital target for 15 min/5 days against MS fatigue. An across-diseases meta-analysis devoted to the Sham effect provided references for power analysis in future tDCS RCTs on these clinical conditions. High-quality indications support tDCS as a promising tool to build electroceutical treatments against diseases involving neurodynamics alterations.

Contributions of the Right Prefrontal and Parietal Cortices to the Attentional Blink: A tDCS Study

The AB refers to the performance impairment that occurs when visual selective attention is overloaded through the very rapid succession of two targets (T1 and T2) among distractors by using the rapid serial visual presentation task (RSVP). Under these conditions, performance is typically impaired when T2 is presented within 200–500 ms from T1 (AB). Based on neuroimaging studies suggesting a role of top-down attention and working memory brain hubs in the AB, here we potentiated via anodal or sham tDCS the activity of the right DLPFC (F4) and of the right PPC (P4) during an AB task. The findings showed that anodal tDCS over the F4 and over P4 had similar effects on the AB. Importantly, potentiating the activity of the right frontoparietal network via anodal tDCS only benefitted poor performers, reducing the AB, whereas in good performers it accentuated the AB. The contribution of the present findings is twofold: it shows both top-down and bottom-up contributions of the right frontoparietal network in the AB, and it indicates that there is an optimal level of excitability of this network, resulting from the individual level of activation and the intensity of current stimulation.

Glial cells have more important role in tDCS-induced brain activities rather than neurons

Transcranial Direct Current Stimulation (tDCS) is a non-invasive and sub-threshold method for altering the excitability of neurons to achieve target conditions. Many clinical applications of tDCS are in progress including treatment of neurological disease. Despite the therapeutic and practical potentials of tDCS, the precise mechanism of its impact is still unclear to a large extent. The initial perspective about the effect of tDCS on synaptic plasticity was that electric stimulation of the brain degrades the threshold of neural firing, thus facilitating electrical transmission and improving conductivity between neurons and ultimately leading to changes in the processing of information. However, new results of some experimental studies have changed the initial perspective. Recently, calcium imaging has shown sudden calcium fluctuations, followed by a change in cortical metaplasticity under tDCS. These pieces of evidence pinpoint the important role of astrocytes in describing the effect of tDCS. Astrocytes are glial cells that are traditionally viewed with only a supportive and nutritional role, but recent research expresses that they are active and contribute to processing and regulating synaptic information. We hypothesize that considering astrocytes as an important player in tDCS effect instead of the direct effect on voltage membrane of neurons is closer to the reality of tDCS effect mechanism. This hypothesis is examined here based on the experimental evidence published so far, which indicates astroglia involvement in tDCS-induced activities and results of our proposed computational model.

Transcranial electrical stimulation improves cognitive training effects in healthy elderly adults with low cognitive performance

OBJECTIVE

To investigate the efficacy of transcranial direct (tDCS) or alternating current stimulation (tACS) in boosting cognitive training efficiency in healthy older adults. We further explored whether such improvements depend on general cognitive performance or age.

METHODS

In this randomized, sham-controlled study, 59 healthy elderly participants (mean age 71.7) were assigned to receive computer-based cognitive training (10 sessions, 50 min, twice weekly) combined with tDCS (2 mA), tACS (5 Hz), or sham stimulation over the left dorsolateral prefrontal cortex (20 minutes). Cognitive performance was assessed with the Montreal Cognitive Assessment (MoCA), and a cognitive composite score derived from a broad neuropsychological test battery before and immediately after the intervention as well as at 6 and 12 months follow-ups.

RESULTS

Performance in the cognitive composite score improved significantly in all groups but was not further modulated by neurostimulation. Additional analyses revealed that participants with a low initial MoCA score (<1SD) improved significantly more in the tDCS than in the sham group.

CONCLUSION

TDCS increased the efficacy of cognitive training, but only in participants with initially low general cognitive performance.

SIGNIFICANCE

Cognitive interventions including tDCS should address baseline performance as modulating factor of cognitive outcomes.

Cathodal Transcranial Direct Current Stimulation Over the Right Temporoparietal Junction Suppresses Its Functional Connectivity and Reduces Contralateral Spatial and Temporal Perception

The temporoparietal junction plays key roles in vestibular function, motor-sensory ability, and attitude stability. Conventional approaches to studying the temporoparietal junction have drawbacks, and previous studies have focused on self-motion rather than on vestibular spatial perception. Using transcranial direct current stimulation, we explored the temporoparietal junction’s effects on vestibular-guided orientation for self-motion and vestibular spatial perception. Twenty participants underwent position, motion, and time tasks, as well as functional magnetic resonance imaging scans. In the position task, cathodal transcranial direct current stimulation yielded a significantly lower response in the −6, −7, −8, −9, −10, −11, and −12 stimulus conditions for leftward rotations (P < 0.05). In the time task, the temporal bias for real transcranial direct current stimulation significantly differed from that for sham stimulation (P < 0.01). Functional magnetic resonance imaging showed that cathodal transcranial direct current stimulation suppressed functional connectivity between the temporoparietal junction, right insular cortex, and right supplementary motor area. Moreover, the change in connectivity between the right temporoparietal junction seed and the right insular cortex was positively correlated with temporal bias under stimulation. The above mentioned results show that cathodal transcranial direct current stimulation induces immediate and extended vestibular effects, which could suppress the functional connectivity of the temporoparietal junction and in turn reduce contralateral spatial and temporal perception. The consistent variation in temporal and spatial bias suggested that the temporoparietal junction may be the cortical temporal integrator for the internal model. Moreover, transcranial direct current stimulation could modulate the integration process and may thus have potential clinical applications in vestibular disorders caused by temporoparietal junction dysfunction.

Hot and cold executive functions in the brain: A prefrontal-cingular network

Executive functions, or cognitive control, are higher-order cognitive functions needed for adaptive goal-directed behaviours and are significantly impaired in majority of neuropsychiatric disorders. Different models and approaches are proposed for describing how executive functions are functionally organised in the brain. One popular and recently proposed organising principle of executive functions is the distinction between hot (i.e. reward or affective-related) versus cold (i.e. purely cognitive) domains of executive functions. The prefrontal cortex is traditionally linked to executive functions, but on the other hand, anterior and posterior cingulate cortices are hugely involved in executive functions as well. In this review, we first define executive functions, their domains, and the appropriate methods for studying them. Second, we discuss how hot and cold executive functions are linked to different areas of the prefrontal cortex. Next, we discuss the association of hot versus cold executive functions with the cingulate cortex, focusing on the anterior and posterior compartments. Finally, we propose a functional model for hot and cold executive function organisation in the brain with a specific focus on the fronto-cingular network. We also discuss clinical implications of hot versus cold cognition in major neuropsychiatric disorders (depression, schizophrenia, anxiety disorders, substance use disorder, attention-deficit hyperactivity disorder, and autism) and attempt to characterise their profile according to the functional dominance or manifest of hot-cold cognition. Our model proposes that the lateral prefrontal cortex along with the dorsal anterior cingulate cortex are more relevant for cold executive functions, while the medial-orbital prefrontal cortex along with the ventral anterior cingulate cortex, and the posterior cingulate cortex are more closely involved in hot executive functions. This functional distinction, however, is not absolute and depends on several factors including task features, context, and the extent to which the measured function relies on cognition and emotion or both.

Modulation of Repeated Anodal HD-tDCS on Attention in Healthy Young Adults

High-definition transcranial direct current stimulation (HD-tDCS) is a valid brain stimulation technology to optimize cognitive function. Recent evidence indicates that single anodal tDCS session enhances attention; however, the variation in attention produced by repeated anodal HD-tDCS over a longer period of time has not been explored. We examined the modulation of attention function in healthy young participants (39 young adults) who received repeated HD-tDCS sustained for 4 weeks. The results showed a robust benefit of anodal HD-tDCS on executive control and psychomotor efficiency, but not on orienting, alerting, or selective attention (inhibition); the benefit increased successively over 4 weeks; and the enhancement on executive control of each week was significant compared to baseline in the anodal group. In addition, the subjects' performances on the test of executive control and psychomotor efficiency gradually restored to the initial level in the sham group, which appeared obviously from week 3 (after 9 interventions), but the improvement of attention in the anodal group was persistent. We conclude that repeated anodal HD-tDCS provides a positive benefit on executive control and psychomotor efficiency and has obvious accumulative effect after 9 or more times intervention compared to sham HD-tDCS. Additionally, our findings might provide pivotal guidance for the formulation of a strategy for the use of repeated anodal HD-tDCS to modulate on attention function.

Distress intolerance mediates attentional control on posttraumatic stress symptoms: Evidence from two clinical samples

Theoretical models emphasize the importance of both affective and cognitive risk factors in the development of posttraumatic stress symptoms (PTSS). Two such factors predicting PTSS have been studied extensively: distress intolerance (DI) - an affective factor indicative of the ability to tolerate negative affective states - and attentional control (AC), a cognitive factor reflecting the ability to flexibly shift and maintain attention to goal-relevant tasks. Previous work primarily highlights the independent contributions of DI and AC and their interaction to predict PTSS. Some models, however, suggest a mediational pathway such that AC indirectly affects PTSS via diminished DI. The current paper addressed this gap by first attempting to replicate prior findings, while also exploring this mediation model. Results were examined in two clinical samples - a trauma-exposed sample of adults (study 1; N = 73) and trauma-exposed treatment-seeking adults (study 2; N = 204). Results partially supported our hypotheses; both studies failed to replicate prior moderation findings, but our mediational hypothesis was supported in both samples. Low AC appears to decrease an individual's tolerance for distressing situations, which in turn increases the severity of PTSS. Results suggest that PTSD treatments may benefit by incorporating components of AC, DI, or a combination of the two to mitigate PTSS. Taken together, this study provides a novel examination of how cognitive and affective risk factors, namely AC and DI, work in tandem to increase PTSS.

An Integrative Clustering Approach to tDCS Individual Response Variability in Cognitive Performance: Beyond a Null Effect on Working Memory

Despite the growing interest in the use of transcranial direct current stimulation (tDCS) for the modulation of human cognitive function, there are contradictory findings regarding the cognitive benefits of this technique. Inter-individual response variability to tDCS may play a significant role. We explored the effects of anodal versus sham tDCS over the left prefrontal cortex (LPFC) on working memory performance, taking into account the inter-individual variability. Twenty-nine healthy volunteers received an 'offline' anodal tDCS (1.5 mA, 15 min) to the left prefrontal cortex (F3 electrode site) in an intra-individual, cross-over, sham-controlled experimental design. n-back and Sternberg task performance was assessed before (baseline), immediately after tDCS administration (T1) and 5 min post-T1 (T2). We applied an integrative clustering approach to characterize both the group and individual responses to tDCS, as well as identifying naturally occurring subgroups that may be present within the total sample. Anodal tDCS failed to improve working memory performance in the total sample. Cluster analysis identified a subgroup of 'responders' who significantly improved their performance after anodal (vs. sham) stimulation, although not to a greater extent than the best baseline or sham condition. The proportion of 'responders' ranged from 15% to 59% across task conditions and behavioral outputs. Our findings show a high inter-individual variability of the tDCS response, suggesting that the use of tCDS may not be an effective tool to improve working memory performance in healthy subjects. We propose that the use of clustering methods is more suitable in identifying 'responders' and for evaluating the efficacy of this technique.

The Effects of Anodal Transcranial Direct Current Stimulation on Sleep Time and Efficiency

A single session of anodal transcranial direct current stimulation (tDCS) has been shown to increase arousal in healthy participants for up to 24 h post-stimulation. However, little is known about the effects of tDCS on subsequent sleep in this population. Based on previous clinical studies, we hypothesized that anodal stimulation to the left dorsolateral prefrontal cortex (lDLPFC) would produce higher arousal with decreased sleep time and stimulation to the primary motor cortex (M1) would have the converse effect. Thirty-six active duty military were randomized into one of three groups (n = 12/group); active anodal tDCS over the lDLPFC, active anodal tDCS over left M1, or sham tDCS. Participants answered questionnaires 3 times a day and wore a wrist activity monitor (WAM) to measure sleep time and efficiency for 3 weeks. On weeks 2 and 3 (order counterbalance), participants received stimulation at 1800 h before 26 h of sustained wakefulness testing (sleep deprived) and at 1800 h without sleep deprivation (non-sleep deprived). There were no significant effects for the non-sleep deprived portion of testing. For the sleep deprived portion of testing, there were main effects of group and night on sleep time. The DLPFC group slept less than the other groups on the second and third night following stimulation. There is no negative effect on mood or sleep quality from a single dose of tDCS when participants have normal sleep patterns (i.e., non-sleep deprived portion of testing). The results suggest that stimulation may result in faster recovery from fatigue caused by acute periods of sleep deprivation, as their recovery sleep periods were less.

Neurotechnologies for Human Cognitive Augmentation: Current State of the Art and Future Prospects

Recent advances in neuroscience have paved the way to innovative applications that cognitively augment and enhance humans in a variety of contexts. This paper aims at providing a snapshot of the current state of the art and a motivated forecast of the most likely developments in the next two decades. Firstly, we survey the main neuroscience technologies for both observing and influencing brain activity, which are necessary ingredients for human cognitive augmentation. We also compare and contrast such technologies, as their individual characteristics (e.g., spatio-temporal resolution, invasiveness, portability, energy requirements, and cost) influence their current and future role in human cognitive augmentation. Secondly, we chart the state of the art on neurotechnologies for human cognitive augmentation, keeping an eye both on the applications that already exist and those that are emerging or are likely to emerge in the next two decades. Particularly, we consider applications in the areas of communication, cognitive enhancement, memory, attention monitoring/enhancement, situation awareness and complex problem solving, and we look at what fraction of the population might benefit from such technologies and at the demands they impose in terms of user training. Thirdly, we briefly review the ethical issues associated with current neuroscience technologies. These are important because they may differentially influence both present and future research on (and adoption of) neurotechnologies for human cognitive augmentation: an inferior technology with no significant ethical issues may thrive while a superior technology causing widespread ethical concerns may end up being outlawed. Finally, based on the lessons learned in our analysis, using past trends and considering other related forecasts, we attempt to forecast the most likely future developments of neuroscience technology for human cognitive augmentation and provide informed recommendations for promising future research and exploitation avenues.

Consecutive sessions of transcranial direct current stimulation do not remediate visual hallucinations in Lewy body dementia: a randomised controlled trial

BACKGROUND

Complex visual hallucinations are common in Lewy body dementia (LBD) and can cause significant patient and caregiver distress. Current treatments are primarily pharmacological in nature and have limited efficacy and associated side effects. The objective of this study was to assess the effects of consecutive sessions of transcranial direct current stimulation (tDCS) on visual hallucination frequency and severity in LBD, at short-term and long-term follow-up stages.

METHODS

The study was a randomised, double-blind, placebo-controlled trial involving 40 participants with LBD (Mage = 75.52 years, SDage = 8.69 years) which was conducted at a single site between November 2013 and December 2017. Participants received two consecutive 20-min sessions of active (0.048 mA/cm2) or placebo tDCS, separated by a 30-min break, over 5 consecutive days. The anodal electrode was applied to the right parietal cortex (P4) and the cathodal electrode was applied to the occipital cortex (Oz). The primary outcome measure was the Neuropsychiatric Inventory (NPI) hallucinations subscale, as completed by a caregiver/informant at baseline and day 5 (short-term) follow-up, and month 1 and month 3 (long-term) follow-up. Secondary outcome measures included visual cortical excitability, as measured using transcranial magnetic stimulation, computerised attentional and visuoperceptual tasks, and measures of global cognition and cognitive fluctuations.

RESULTS

Complete study data were obtained from 36 participants. There was an overall improvement in visual hallucinations (NPI) for both groups at day 5 relative to baseline, with a medium-to-large effect size; however, compared to placebo, active tDCS did not result in any improvements in visual hallucinations (NPI) at day 5 relative to baseline, or at month 1 or month 3 follow-up time points. Additionally, comparisons of secondary outcome measures showed that active tDCS did not result in any improvements on any measure (visual cortical excitability, attentional and visuoperceptual tasks or cognitive measures) at any time point.

CONCLUSIONS

Repeated consecutive sessions of parietal anodal tDCS, and occipital cathodal tDCS, do not improve visual hallucinations or visuoperceptual function, or alter visual cortical excitability in LBD.

TRIAL REGISTRATION

ISRCTN, ISRCTN40214749 . Registered on 25 October 2013.

Bias Toward Drug-Related Stimuli Is Affected by Loading Working Memory in Abstinent Ex-Methamphetamine Users

Background: There is a trade-off between drug-related impulsive process and cognitive reflective process among ex-drug abusers. The present study aimed to investigate the impulsive effects of methamphetamine-related stimuli on working memory (WM) performance by manipulating WM load in abstinent ex-methamphetamine users. Methods: Thirty abstinent ex-methamphetamine users and 30 nonaddict matched control participants were recruited in this study. We used a modified Sternberg task in which participants were instructed to memorize three different sets of methamphetamine-related and non-drug-related words (three, five, or seven words) while performing a secondary attention-demanding task as an interference. Results: Repeated-measures ANOVA revealed that reaction times of abstinent ex-methamphetamine users increased during low WM load (three words) compared to the control group (p = 0.01). No significant differences were observed during high WM loads (five or seven words) (both p's > 0.1). Besides, reaction times of the experimental group during trials with high interference (three, five, or seven words) were not significantly different compared to the control group (p > 0.2). Conclusion: These findings imply that increasing WM load may provide an efficient buffer against attentional capture by salient stimuli (i.e., methamphetamine-related words). This buffer might modify the effect of interference bias. Besides, presenting methamphetamine-related stimuli might facilitate the encoding phase due to bias toward task-relevant stimuli. This finding has an important implication, suggesting that performing concurrent demanding tasks may reduce the power of salient stimuli and thus improve the efficiency of emotional regulation strategies.

Concomitant Transcranial Direct Current Stimulation With Ultrabrief Electroconvulsive Therapy: A 2-Week Double-Blind Randomized Sham-Controlled Trial

OBJECTIVE

The feasibility and effectiveness of concomitant use of transcranial direct current stimulation (tDCS) with electroconvulsive therapy (ECT) has not been investigated. The study principally aimed at determining whether tDCS when combined with ECT improved the speed of antidepressant response. Secondarily, the ease of generation of seizures during electroconvulsive therapy and cognitive outcomes were investigated.

METHODS

Consecutive patients referred for ECT to treat major depression were randomized to tDCS with dorsolateral prefrontal electrode placements (n = 8) or sham (n = 8) used daily and just before thrice weekly, 6 times threshold, right unilateral ultrabrief (0.3 ms) pulse width ECT. Change of depression severity was determined using the Montgomery Asberg Depression Rating Scale along with cognitive assessments using Montreal Cognitive Assessment and visual memory testing at weeks 1 and 2, which were compared with baseline.

RESULTS

Change of depression severity from baseline was similar in tDCS and ECT compared with sham tDCS and ECT at week1 (mean [standard deviation {SD}] = 16.00 [6.78]; 13.75 [7.83]; P = 0.89) and at week 2 (mean [SD] = 23.00 [4.96]; 19.75 [9.85], P = 0.08). No between-group differences were obtained in the cognitive tests at weeks 1 and 2. Combining tDCS with ECT resulted in higher restimulation: 62.5% requiring 3 stimulations to achieve threshold in contrast to 12.5% with sham tDCS and ECT (P = 0.04). The mean suprathreshold dose was higher in the tDCS and ECT group compared with sham tDCS and ECT: mean [SD] = 144.0 [43.54] and mean [SD] = 122.4 [20.36], P = 0.04, respectively.

CONCLUSIONS

Concomitant use of tDCS with ultrabrief right unilateral ECT is feasible and safe albeit with higher rates of restimulation when tDCS was combined with ECT. However, there were no statistically significant differences in the speed of antidepressant response or cognitive outcomes at weeks 1 and 2 after the commencement of treatments.

Modulating the excitability of the visual cortex using a stimulation priming paradigm

BACKGROUND

Transcranial random noise stimulation (tRNS) can cause long term increase of corticospinal excitability when used to prime the motor cortex, before measuring the motor response in the hand muscles with TMS (Terney et al., 2008). In cognitive studies, tRNS has been used to improve visual attention and mathematical skills, an enhancement effect that might suggest sustained cortical plasticity changes (Cappelletti et al., 2013; Snowball et al., 2013). However, while the behavioral evidence of increased performance is becoming substantiated by empirical data, it still remains unclear whether tRNS over visual areas causes an increase in cortical excitability similar to what has been found in the motor cortex, and if that increase could be a potential physiological explanation for behavioral improvements found in visual tasks.

OBJECTIVE/HYPOTHESIS

In the present study, we aimed to investigate whether priming the visual cortex with tRNS leads to increased and sustained excitability as measured with visual phosphenes.

METHODS

We measured phosphene thresholds (PTs) using an objective staircase method to quantify the magnitude of cortical excitability changes. Single-pulse TMS was used to elicit phosphenes before, immediately after, and every 10 min up to one hour after the end of 20 min tRNS, anodal tDCS (a-tDCS) or sham.

RESULTS

Results showed that phosphene thresholds were significantly reduced up to 60 min post stimulation relative to baseline after tRNS, a behavioral marker of increased excitability of the visual cortex, while a-tDCS had no effect. This result is very similar in magnitude and duration to what has been found in the motor cortex.

CONCLUSIONS

Our findings demonstrate promising potential of tRNS as a tool to increase and sustain cortical excitability to promote improvement of cognitive functions.

The Efficacy of Transcranial Current Stimulation Techniques to Modulate Resting-State EEG, to Affect Vigilance and to Promote Sleepiness

Transcranial Current Stimulations (tCSs) are non-invasive brain stimulation techniques which modulate cortical excitability and spontaneous brain activity by the application of weak electric currents through the scalp, in a safe, economic, and well-tolerated manner. The direction of the cortical effects mainly depend on the polarity and the waveform of the applied current. The aim of the present work is to provide a broad overview of recent studies in which tCS has been applied to modulate sleepiness, sleep, and vigilance, evaluating the efficacy of different stimulation techniques and protocols. In recent years, there has been renewed interest in these stimulations and their ability to affect arousal and sleep dynamics. Furthermore, we critically review works that, by means of stimulating sleep/vigilance patterns, in the sense of enhancing or disrupting them, intended to ameliorate several clinical conditions. The examined literature shows the efficacy of tCSs in modulating sleep and arousal pattern, likely acting on the top-down pathway of sleep regulation. Finally, we discuss the potential application in clinical settings of this neuromodulatory technique as a therapeutic tool for pathological conditions characterized by alterations in sleep and arousal domains and for sleep disorders per se.

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.

Concurrent measurement of cerebral hemodynamics and electroencephalography during transcranial direct current stimulation

Transcranial direct current stimulation (tDCS) is currently being used for research and treatment of some neurological and neuropsychiatric disorders, as well as for improvement of cognitive functions. In order to better understand cerebral response to the stimulation and to redefine protocols and dosage, its effects must be monitored. To this end, we have used functional diffuse correlation spectroscopy (fDCS) and time-resolved functional near-infrared spectroscopy (TR-fNIRS) together with electroencephalography (EEG) during and after stimulation of the frontal cortex. Twenty subjects participated in two sessions of stimulation with two different polarity montages and twelve also underwent a sham session. Cerebral blood flow and oxyhemoglobin concentration increased during and after active stimulation in the region under the stimulation electrode while deoxyhemoglobin concentration decreased. The EEG spectrum displayed statistically significant power changes across different stimulation sessions in delta (2 to 4 Hz), theta (4 to 8 Hz), and beta (12 to 18 Hz) bands. Results suggest that fDCS and TR-fNIRS can be employed as neuromonitors of the effects of transcranial electrical stimulation and can be used together with EEG.

Transcranial Direct Current Stimulation (tDCS): A Beginner's Guide for Design and Implementation

Transcranial direct current stimulation (tDCS) is a popular brain stimulation method that is used to modulate cortical excitability, producing facilitatory or inhibitory effects upon a variety of behaviors. There is, however, a current lack of consensus between studies, with many results suggesting that polarity-specific effects are difficult to obtain. This article explores some of these differences and highlights the experimental parameters that may underlie their occurrence. We provide a general, practical snapshot of tDCS methodology, including what it is used for, how to use it, and considerations for designing an effective and safe experiment. Our aim is to equip researchers who are new to tDCS with the essential knowledge so that they can make informed and well-rounded decisions when designing and running successful experiments. By summarizing the varied approaches, stimulation parameters, and outcomes, this article should help inform future tDCS research in a variety of fields.

Surface EEG-Transcranial Direct Current Stimulation (tDCS) Closed-Loop System

Conventional transcranial direct current stimulation (tDCS) protocols rely on applying electrical current at a fixed intensity and duration without using surrogate markers to direct the interventions. This has led to some mixed results; especially because tDCS induced effects may vary depending on the ongoing level of brain activity. Therefore, the objective of this preliminary study was to assess the feasibility of an EEG-triggered tDCS system based on EEG online analysis of its frequency bands. Six healthy volunteers were randomized to participate in a double-blind sham-controlled crossover design to receive a single session of 10[Formula: see text]min 2[Formula: see text]mA cathodal and sham tDCS. tDCS trigger controller was based upon an algorithm designed to detect an increase in the relative beta power of more than 200%, accompanied by a decrease of 50% or more in the relative alpha power, based on baseline EEG recordings. EEG-tDCS closed-loop-system was able to detect the predefined EEG magnitude deviation and successfully triggered the stimulation in all participants. This preliminary study represents a proof-of-concept for the development of an EEG-tDCS closed-loop system in humans. We discuss and review here different methods of closed loop system that can be considered and potential clinical applications of such system.

No evidential value in samples of transcranial direct current stimulation (tDCS) studies of cognition and working memory in healthy populations

A substantial number of studies have been published over the last decade, claiming that transcranial direct current stimulation (tDCS) can influence performance on cognitive tasks. However, there is some skepticism regarding the efficacy of tDCS, and evidence from meta-analyses are mixed. One major weakness of these meta-analyses is that they only examine outcomes in published studies. Given biases towards publishing positive results in the scientific literature, there may be a substantial "file-drawer" of unpublished negative results in the tDCS literature. Furthermore, multiple researcher degrees of freedom can also inflate published p-values. Recently, Simonsohn, Nelson and Simmons (2014) created a novel meta-analytic tool that examines the distribution of significant p-values in a literature, and compares it to expected distributions with different effect sizes. Using this tool, one can assess whether the selected studies have evidential value. Therefore, we examined a random selection of studies that used tDCS to alter performance on cognitive tasks, and tDCS studies on working memory in a recently published meta-analysis (Mancuso et al., 2016). Using a p-curve analysis, we found no evidence that the tDCS studies had evidential value (33% power or greater), with the estimate of statistical power of these studies being approximately 14% for the cognitive studies, and 5% (what would be expected from randomly generated data) for the working memory studies. It is likely that previous tDCS studies are substantially underpowered, and we provide suggestions for future research to increase the evidential value of future tDCS studies.

The Effects of Transcranial Direct Current Stimulation (tDCS) on Multitasking Throughput Capacity

Background: Multitasking has become an integral attribute associated with military operations within the past several decades. As the amount of information that needs to be processed during these high level multitasking environments exceeds the human operators' capabilities, the information throughput capacity reaches an asymptotic limit. At this point, the human operator can no longer effectively process and respond to the incoming information resulting in a plateau or decline in performance. The objective of the study was to evaluate the efficacy of a non-invasive brain stimulation technique known as transcranial direct current stimulation (tDCS) applied to a scalp location over the left dorsolateral prefrontal cortex (lDLPFC) to improve information processing capabilities during a multitasking environment. Methods: The study consisted of 20 participants from Wright-Patterson Air Force Base (16 male and 4 female) with an average age of 31.1 (SD = 4.5). Participants were randomly assigned into two groups, each consisting of eight males and two females. Group one received 2 mA of anodal tDCS and group two received sham tDCS over the lDLPFC on their testing day. Results: The findings indicate that anodal tDCS significantly improves the participants' information processing capability resulting in improved performance compared to sham tDCS. For example, the multitasking throughput capacity for the sham tDCS group plateaued near 1.0 bits/s at the higher baud input (2.0 bits/s) whereas the anodal tDCS group plateaued near 1.3 bits/s. Conclusion: The findings provided new evidence that tDCS has the ability to augment and enhance multitasking capability in a human operator. Future research should be conducted to determine the longevity of the enhancement of transcranial direct current stimulation on multitasking performance, which has yet to be accomplished.

Increased contextual cue utilization with tDCS over the prefrontal cortex during a recognition task

The precise role of the prefrontal and posterior parietal cortices in recognition performance remains controversial, with questions about whether these regions contribute to recognition via the availability of mnemonic evidence or via decision biases and retrieval orientation. Here we used an explicit memory cueing paradigm, whereby external cues probabilistically predict upcoming memoranda as old or new, in our case with 75% validity, and these cues affect recognition decision biases in the direction of the cue. The present study applied bilateral transcranial direct current stimulation (tDCS) over prefrontal or posterior parietal cortex, or sham tDCS, to test the causal role of these regions in recognition accuracy or decision biasing. Participants who received tDCS over prefrontal cortex showed increased cue utilization compared to tDCS over posterior parietal cortex and sham tDCS, suggesting that the prefrontal cortex is involved in processes that contribute to decision biases in memory.

Transcranial Direct Current Stimulation over the Parietal Cortex Improves Approximate Numerical Averaging

The parietal cortex has been implicated in a variety of numerosity and numerical cognition tasks and was proposed to encompass dedicated neural populations that are tuned for analogue magnitudes as well as for symbolic numerals. Nonetheless, it remains unknown whether the parietal cortex plays a role in approximate numerical averaging (rapid, yet coarse computation of numbers' mean)—a process that is fundamental to preference formation and decision-making. To causally investigate the role of the parietal cortex in numerical averaging, we have conducted a transcranial direct current stimulation (tDCS) study, in which participants were presented with rapid sequences of numbers and asked to convey their intuitive estimation of each sequence's average. During the task, the participants underwent anodal (excitatory) tDCS (or sham), applied either on a parietal or a frontal region. We found that, although participants exhibit above-chance accuracy in estimating the average of numerical sequences, they did so with higher precision under parietal stimulation. In a second experiment, we have replicated this finding and confirmed that the effect is number-specific rather than domain-general or attentional. We present a neurocomputational model postulating population-coding underlying rapid numerical averaging to account for our findings. According to this model, stimulation of the parietal cortex elevates neural activity in number-tuned dedicated detectors, leading to increase in the system's signal-to-noise level and thus resulting in more precise estimations.