The tolerability of transcranial electrical stimulation used across extended periods in a naturalistic context by healthy individuals

Is it safe? Obviously the test wasn’t designed to assess any possible negative cognitive effects, but apart from some, “skin tingling, itching, and mild burning sensations” the subjects tolerated frequent TES (transcranial electric stimulation) well.

In the present study, we tested the tolerability (safety) and compliance, compared to sham, of two common tES approaches having a current density < 2 mA/cm2; transcranial Direct Current Stimulation (tDCS) or transcranial Pulsed Current Stimulation (tPCS) used by healthy subjects three to five days (17 – 20 minutes per day) per week for up to six weeks in a naturalistic environment. In this study 100 healthy subjects were randomized to one of three treatment groups: tDCS (n = 33), tPCS (n = 30), or sham (n = 37) and blinded to the treatment condition. The tES and sham waveforms were delivered through self-adhering electrodes on the right lateral forehead and back of the neck. We conducted 1905 treatment sessions (636 sham, 623 tDCS, and 646 tPCS sessions) on study volunteers over a six-week period. There were no serious adverse events in any treatment condition.

Source: https://peerj.com/preprints/1097/

Major Study Finds No tDCS Benefit To Fluid Intelligence Training

Update: Aldis wrote in a comment:

To clarify the takeaway message: we weren’t actually training fluid intelligence. Fluid intelligence has been shown to rely on fundamental cognitive abilities like working memory and attention, and the games were designed to train those underlying abilities. Training on fluid intelligence tasks would be like teaching to the test.

In a talk, “Can HD-tDCS Enhance Cognitive Training”, Aldis Sipolins describes a ‘wildly ambitious’ cognitive training study called the INSIGHT Project. Funded by IARPA, the study combined rigorous exercise and HD-tDCS-enhanced cognitive training in an attempt to increase ‘fluid intelligence’. 518 subjects, half of whom underwent pre and post fMRI scanning, undertook a 16 week course of combined exercise and brain training. The results? Anodal HD-tDCS improved performance on 3 of 6 brain-training video games but had no effect on transfer, i.e. the improvements did not transfer to general intelligence. As a result tDCS will not be a part of the study moving forward.

  • Partnered with Aptima to create a suite of six brain-training games. Games were ‘adaptive’, i.e they increased in difficulty as the subject’s performance improved.
  • Montage used was  2 x 2 (4 electrodes) designed by Soterix to affect DLPFC (dorsalateral prefrontal cortex). Dosage was 2mA for 30 minutes. Training started once current ramped up.
  • BOMAT (bochumer matrices) test was used to determine whether enhanced game performance transferred to fluid intelligence.
  • A future study on the INSIGHT Project will include a Mindfulness meditation segment and include nutritional supplements (brain shake).

In a recent Reddit thread when asked what he’d do differently, Aldis Sipolins said:

1) Include a cathodal group, with the hope that it impairs performance. Vince Clark suggested that impairing performance during cognitive training may have led to greater transfer. Kind of like how strapping weights to your body when you train makes it easier to move once you take them off.

2) Include a tDCS group that doesn’t complete the exercise intervention. It’s possible that exercise masked the effects of tDCS.

I would personally like to thank Aldis Sipolins, Art Kramer, and everyone at the Lifelong Brain and Cognition lab for some excellent science!

 

A mood-changing headset, Thync, that uses electrodes to perk you up | The Guardian

Also, if you live in the Boston area, Thync is recruiting for alpha-testing. https://www.surveymonkey.com/s/AlphaRecruitment

Alcohol and coffee are about to get competition from a set of electrodes you wear on your head. Branded the Thync, the calming effect it produces is comparable to how you feel after an alcoholic drink, while the energising effect is similar to a cup of coffee, says Isy Goldwasser, the CEO and co-founder of this Silicon Valley-based startup. The company plans to start selling the device through its website in 2015.
Goldwasser envisages people using the Thync “vibes” to help them unwind after a long day at work, or to get a caffeine-free pick-me-up. “We are giving people a way to overcome a basic limitation – that no one is really wired to co-opt energy and calm on demand,” he says.
It doesn’t work for everyone though. About a third of people don’t have a strong response. When I try a prototype I feel a tingling where it makes contact with my skin, but no particularly serene feeling, even after a few sessions. The energising vibe also fails to do much for me.

via A mood-changing headset, Thync, that uses electrodes to perk you up | Technology | The Guardian.

Study set for brain stimulation device to help restore memory – The Washington Post

Not tDCS but fascinating…

Medtronic [a medical device manufacturer] will be developing a 256-channel brain stimulator, not only to stimulate but to record and analyze brain activity and [to] try to modify and synthesize it within the brain.

The ultimate goal is to send patients with memory disorders home with a device implanted into their brain to improve their memory.

How will the study work?

The 256-channel device will be far more than a brain stimulator. It will be an intelligent device that continuously monitors brain function for signals that indicate how well our memory system is operating. As it tracks these signals, in real time, it will use mathematical models of brain function to determine whether and how to stimulate at each of these locations. By cycling very rapidly between recording, analyzing and stimulating, it will try to continuously maintain good memory function in patients with neurological injury or disease.

via Study set for brain stimulation device to help restore memory – The Washington Post.

Hits and misses: leveraging tDCS to advance cognitive research

Excellent study. Confirming once again how early we are in our understanding of tDCS. (emphasis below are mine).

Although these studies all report positive findings there is still considerable variability in terms of the pattern of effects, paradigms used and tDCS parameters. For instance, stimulus intensity, duration, tDCS electrode montage are inconsistent. The most consistent pattern in the published literature has been to report significant improvements in WM tested in verbal n-back tasks and anodal tDCS to the left DLPFC. In other cognitive realms a patchwork of findings is emerging revealing consistent effects in memory, deception, and cognitive control. However, there are exceptions and forays into different tasks, populations, and parameters have produced different patterns of results.

via Hits and misses: leveraging tDCS to advance cognitive research.

Brain stimulation for your stammer | University of Oxford

OSB: What is the aim of your new trial?

JC: In this study, we want to see how the effects of a brief course of fluency therapy might be increased or prolonged by using TDCS. We will use some techniques that we know will immediately increase fluency in most people who stammer, such as speaking in unison with another person or in time with a metronome. However, these techniques would normally need to be combined with other methods to help transfer this fluency into everyday speech. We will investigate how TDCS might help maintain the fluent speech that is produced using these methods.

OSB: What will volunteers be asked to do?

JC: Volunteers will be invited to have fluency therapy over five consecutive days, whilst receiving TDCS. In order to measure the effects of this intervention, they will also be asked to do some speech tasks before the fluency therapy, one week after the fluency therapy, and again six weeks later. We are also interested in how this combination of therapy and TDCS may change brain function and structure. So, volunteers will also be invited for MRI scans before and after the therapy.

via Brain stimulation for your stammer | University of Oxford.

LONG-TERM EFFECTS OF TRANSCRANIAL DIRECT CURRENT STIMULATION IN CHRONIC POST-STROKE APHASIA: A PILOT STUDY | Frontiers in Human Neuroscience

At the end of the stimulation period we found a significant beneficial effect of A-tDCS as compared to baseline and S-tDCS in all our subjects, regardless of word difficulty, although with some inter-individual differences. In the follow-up period, the percentage of correct responses persisted significantly better until the 16th week, when an initial decline in naming performance was observed. Up to the 21st week, the number of correct responses, though no longer significant, was still above the baseline level. These results in a small group of aphasic patients suggest a long-term beneficial effect of on-line A-tDCS.

via Frontiers | LONG-TERM EFFECTS OF TRANSCRANIAL DIRECT CURRENT STIMULATION IN CHRONIC POST-STROKE APHASIA: A PILOT STUDY | Frontiers in Human Neuroscience.

Transcranial direct current stimulation facilitates cognitive multi-task performance differentially depending on anode location and subtask | Frontiers in Human Neuroscience

Interesting especially in relation to Michael Weisend’s success using F10 in skill (target recognition) acquisition. That the research is going in this direction is encouraging. I expect we’ll have a much better understanding of various cognitive enhancement strategies over the next few years.

We compared effects of 30 min prefrontal and parietal stimulation to right and left hemispheres on subtask performance during the first 45 min of training. The strongest effects both overall and for ship flying control and velocity subtasks were seen with a right parietal C4, reference to left shoulder montage, shown by modeling to induce an electric field that includes nodes in both dorsal and ventral attention networks. This is consistent with the re-orienting hypothesis that the ventral attention network is activated along with the dorsal attention network if a new, task-relevant event occurs while visuospatial attention is focused Corbetta et al., 2008. No effects were seen with anodes over sites that stimulated only dorsal C3 or only ventral F10 attention networks. The speed subtask update memory for symbols benefited from an F9 anode over left prefrontal cortex. These results argue for development of tDCS as a training aid in real world settings where multi-tasking is critical.

via Frontiers | Transcranial direct current stimulation facilitates cognitive multi-task performance differentially depending on anode location and subtask | Frontiers in Human Neuroscience.

Polarity Specific Suppression Effects of Transcranial Direct Current Stimulation for Tinnitus

Tinnitus is the perception of a sound in the absence of an external auditory stimulus and affects 10–15% of the Western population. Previous studies have demonstrated the therapeutic effect of anodal transcranial direct current stimulation tDCS over the left auditory cortex on tinnitus loudness, but the effect of this presumed excitatory stimulation contradicts with the underlying pathophysiological model of tinnitus. Therefore, we included 175 patients with chronic tinnitus to study polarity specific effects of a single tDCS session over the auditory cortex 39 anodal, 136 cathodal. To assess the effect of treatment, we used the numeric rating scale for tinnitus loudness and annoyance. Statistical analysis demonstrated a significant main effect for tinnitus loudness and annoyance, but for tinnitus annoyance anodal stimulation has a significantly more pronounced effect than cathodal stimulation. We hypothesize that the suppressive effect of tDCS on tinnitus loudness may be attributed to a disrupting effect of ongoing neural hyperactivity, independent of the inhibitory or excitatory effects and that the reduction of annoyance may be induced by influencing adjacent or functionally connected brain areas involved in the tinnitus related distress network. Further research is required to explain why only anodal stimulation has a suppressive effect on tinnitus annoyance.

via Polarity Specific Suppression Effects of Transcranial Direct Current Stimulation for Tinnitus.
HatTip Reddit user matt2001

Electric “thinking cap” controls learning speed

From Vanderbilt University Research News. This article got a lot of traction this week. I would be very curious to see the results of the same study with tDCS applied at the time the tests were being given (rather than before). I’ve heard this described as ‘online’ testing.
Interesting to see Mind Alive’s Oasis Pro device being used clinically.

Reinhart and Woodman set out to test several hypotheses: One, they wanted to establish that it is possible to control the brain’s electrophysiological response to mistakes, and two, that its effect could be intentionally regulated up or down depending on the direction of an electrical current applied to it. This bi-directionality had been observed before in animal studies, but not in humans. Additionally, the researchers set out to see how long the effect lasted and whether the results could be generalized to other tasks.

Beauty and the Brain | Spark with Nora Young | CBC Radio

A little zap to the brain may improve the way you feel about a picture. Neurologist Zaira Cattaneo is the co-author of a new study called The world can look better: enhancing beauty experience with brain stimulation. For the experiment, Zaira and her fellow researchers stimulated the left dorsolateral prefrontal cortex to see if that would enhance the experience of beauty. The results? Listen to her full interview with Nora now!

via Beauty and the Brain | Spark with Nora Young | CBC Radio.
Or read/download the full paper: The world can look better: enhancing beauty experience with brain stimulation

Articles of Note – March 2013

(What happened to February?)
Transcranial Direct Current Stimulation (tDCS) of the visual cortex: a proof-of-concept study based on interictal electrophysiological abnormalities in migraine (pdf)
with anodal tDCS turned out to be beneficial in MoA (migraine without aura patients) migraine attack frequency, migraine days, attack duration and acute medication intake significantly decreased during the treatment period compared to pre-treatment baseline
Tags: Migraine, visual cortex,

The Mental Cost of Cognitive Enhancement (pdf)
Stimulation to the the posterior parietal cortex facilitated numerical learning, whereas automaticity for the learned material was impaired. In contrast, stimulation to the dorsolateral prefrontal cortex impaired the learning process, whereas automaticity for the learned material was enhanced.
Wired Version
New Scientist Version
Tags: Roi Cohen Kadosh,

Keith Spalding’s Simple DIY TDCS circuit using CRDs
A DIY schematic for tDCS using CRDs for current regulation.
Tags: DIY, CRD

Noninvasive transcranial direct current stimulation over the left prefrontal cortex facilitates cognitive flexibility in tool use
…we hypothesized that cathodal (inhibitory) transcranial direct current stimulation (tDCS) will facilitate performance in a flexible use generation task.
The results support the hypothesis that certain tasks may benefit from a state of diminished cognitive control.
Tags: inhibitory benefits,

When Anger Leads to Rumination
Induction of Relative Right Frontal Cortical Activity With Transcranial Direct Current Stimulation Increases Anger-Related Rumination
…results suggest that anger associated with greater relative left frontal cortical activity predicts approach-oriented aggressive action, whereas anger associated with greater relative right frontal cortical activity predicts inhibited rumination.

Potential of transcranial direct current stimulation shown in fibromyalgia
Transcranial direct current stimulation delivered focally to the left primary motor cortex of patients with fibromyalgia significantly reduced perceived pain compared with sham stimulation in a proof-of-principle pilot trial.
Tags, fibromyalgia, pain

February 2013 tDCS Papers of Interest

If there’s no link to a pdf, it means the full paper is behind a paywall. If you find a public link to the full paper, please send it along and I’ll update the post. Did I miss anything 😉
Bold: Paper title, linked to Abstract
(pdf): Direct pdf download where available
Italic: ‘Takeaway’ snippet from abstract.
(Bracketed): My thoughts FWIW
Tags:

Transcranial direct current stimulation increases resting state interhemispheric connectivity.
the tDCS group showed increased DLPFC connectivity to the right hemisphere and decreased DLPFC connectivity to the brain regions around the stimulation site in the left hemisphere. (Lends more credence to the idea of increasing positive effects of tDCS by simultaneously damping down (cathodal) and ramping up (anodal) neuronal activity.)
Tags: theory, learning, enhancement

Transcranial direct current stimulation for treatment of refractory childhood focal epilepsy.
A single session of cathodal tDCS improves epileptic EEG abnormalities for 48 h and is well-tolerated in children.
Tags: epilepsy, children

Brain stimulation modulates the autonomic nervous system, rating of perceived exertion and performance during maximal exercise.
…indicating that the brain plays a crucial role in the exercise performance regulation.
Tags: sports medicine

Evolution of Premotor Cortical Excitability after Cathodal Inhibition of the Primary Motor Cortex: A Sham-Controlled Serial Navigated TMS Study (pdf)
Cathodal inhibition of M1 excitability leads to a compensatory increase of ipsilateral PMC (premotor cortical regions) excitability. (Cathodal tDCS used as a tool to facilitate an experiment)
Tags: theory,

Rethinking Clinical Trials of Transcranial Direct Current Stimulation: Participant and Assessor Blinding Is Inadequate at Intensities of 2mA (pdf) (See also: A big hole in the control? Transcranial direct current stimulation blinding on trial)
Our results suggest that blinding in studies using tDCS at intensities of 2 mA is inadequate. Positive results from such studies should be interpreted with caution.
Tags: theory, sham, blinding,

The effects of cross-hemispheric dorsolateral prefrontal cortex transcranial direct current stimulation (tDCS) on task switching
Task switching, defined as the ability to flexibly switch between tasks in the face of goal shifting, is a central mechanism in cognitive control. …Our findings confirm the notion that involvement of the PFC on task switching depends critically on laterality, implying the existence of different roles for the left hemisphere and the right hemisphere in task switching.
Tags: task switching, theory

The role of timing in the induction of neuromodulation in perceptual learning by transcranial electric stimulation
tRNS (transcranial random noise stimulation) facilitated task performance only when it was applied during task execution, whereas anodal tDCS induced a larger facilitation if it was applied before task execution. (This study showed tDCS to be more effective when applied prior to training! (i.e. ‘offline’)
Tags: tRNS, offliine, online, training, enhancement, perceptual learning

Modulation of verbal fluency networks by transcranial direct current stimulation (tDCS) in Parkinson’s disease
…left dorsolateral prefrontal cortex (DLPFC) tDCS increased performance on the phonemic fluency task
Tags: Parkinson’s, verbal fluency

Transcranial Electrical Currents to Probe EEG Brain Rhythms and Memory Consolidation during Sleep in Humans (2011) (pdf)
…results demonstrate the suitability of oscillating-tDCS as a tool to analyze functions of endogenous EEG rhythms and underlying endogenous electric fields as well as the interactions between EEG rhythms of different frequencies. (Way over my head at this point but trying to understand it, as Lisa Marshall is frequently mentioned in discussions around tDCS and memory. I’m also trying to build an understanding of EEG.)
Tags: memory consolidation, EEG, theory

(pdf) Random Noise Stimulation Improves Neuroplasticity in Perceptual Learning (2011)
Our results confirmed the efficacy of hf-tRNS over the visual cortex in improving behavioral performance and showed its superiority in comparison to other TES. (tRNS transcranial random noise stimulation, has been showing up more often in relation to studies focused on learning and cognition.)
Tags: tRNS, perceptual learning, neural plasticity,

Focal Modulation of the Primary Motor Cortex in Fibromyalgia Using 4×1-Ring High-Definition Transcranial Direct Current Stimulation (HD-tDCS): Immediate and Delayed Analgesic Effects of Cathodal and Anodal Stimulation
4×1-ring HD-tDCS, a novel noninvasive brain stimulation technique capable of more focal and targeted stimulation, provides significant reduction in overall perceived pain in fibromyalgia patients..
Tags: HD-tDCS, Fibromyalgia, pain health

Transcranial direct current stimulation’s effect on novice versus experienced learning (2011)
TDCS was significantly more effective in enhancing test performance when applied in novice learners than in experienced learners.
Tags: learning, threat detection, anode F8,

Evaluation of sham transcranial direct current stimulation for randomized, placebo-controlled clinical trials.
The tDCS sham condition investigated here may be suitable for placebo-controlled trials keeping subjects blind to treatment conditions. (The protocol for sham tDCS is necessarily evolving.)
Tags: sham,

Tremor Suppression by Rhythmic Transcranial Current Stimulation
With this technique we can achieve almost 50% average reduction in resting tremor amplitude and in so doing form the basis of a closed-loop tremor-suppression therapy that could be extended to other oscillopathies. (tACS transcranial alternating current)
Tags: Parkinsons, tremor, tACS

Is Transcranial Alternating Current Stimulation Effective in Modulating Brain Oscillations? (pdf)
Therefore, the present study does not provide significant evidence for tACS reliably inducing direct modulations of brain oscillations that can influence performance in a visual task.
Tags: tACS, posterior parietal cortex, visual perception

Neuromodulation for Brain Disorders: Challenges and Opportunities (pdf)
This article reviews the state-of-the-art of neuromodulation for brain disorders and discusses the challenges and opportunities available for clinicians and researchers interested in advancing neuromodulation therapies. (Excellent overview of where we’re at with various forms of brain stimulation)
Tags: Neuromodulation, brain stimulation, tDCS, DBS (Deep Brain Stimulation), ICS (intracranial cortical stimulation), TMS (transcranial magnetic stimulation)

Improved proper name recall in aging after electrical stimulation of the anterior temporal lobes (2011) (pdf)
The task was to look at pictures of famous faces or landmarks and verbally recall the associated proper name. Our results show a numerical improvement in face naming after left or right ATL stimulation, but a statistically significant effect only after left-lateralized stimulation.
Tags: name recall, anterior temporal lobes, aging,

Transcranial brain stimulation (not sure this link will work for you pdf)
This book reviews recent advances made in the field of brain stimulation techniques. Moreover NIBS techniques exert their effects on neuronal state through different mechanisms at cellular and functional level.
Tags: NIBS (non-invasive brains stimulation), research overview,

Naming facilitation induced by transcranial direct current stimulation. (2010)
…anodal tDCS of the left DLPFC improves naming performance, speeding up verbal reaction times after the end of the stimulation, whereas cathodal stimulation had no effect.
Tags: learning, left DLPFC,

Consolidation of Human Motor Cortical Neuroplasticity by D-Cycloserine (2004) (pdf)
While anodal tDCS enhances motor cortical excitability, cathodal tDCS diminishes it. Both effects seem to be NMDA receptor dependent. D-CYC selectively potentiated the duration of motor cortical excitability enhancements induced by anodal tDCS.(Again, way over my head, but NMDA receptors comes up frequently in the context of tDCS and neurotransmitters.)
Tags: NMDA receptors, D-Cycloserine, learning, enhancement

Interactions between transcranial direct current stimulation (tDCS) and pharmacological interventions in the Major Depressive Episode: Findings from a naturalistic study. (See also: Electrical Brain Stimulation Plus Drug Fights Depression)
…To investigate the interactions between tDCS and drug therapy …tDCS over the DLPFC acutely improved depressive symptoms.
Tags: depression, Zoloft

Physiological and modeling evidence for focal transcranial electrical brain stimulation in humans: A basis for high-definition tDCS.
We provide direct evidence in humans that TES with a 4 × 1-Ring configuration can activate motor cortex and that current does not substantially spread outside the stimulation area.
Tags: HD-tDCS, electrodes, M1

Transcranial Direct Current Stimulation (tDCS) Reduces Postsurgical Opioid Consumption in Total Knee Arthroplasty (TKA).
…tDCS may be able to reduce post-TKA opioid requirements.
Tags: pain,

Modulating lexical and semantic processing by transcranial direct current stimulation.…(tDCS), which is applied over Wernicke’s area and its right homologue, to influence lexical decisions and semantic priming…
Results showed impaired lexical processing under right anodal/left cathodal stimulation in comparison with sham and left anodal/right cathodal stimulation.

tDCS Recent Activity 12/12 – 1/13

A lot of the ‘pop sci’ articles are drawing on the results of only a few studies. Hopefully we’ll get affirmation of the efficacy of tDCS in cognitive enhancement soon.

Does Passing A Small Current Through Your Brain Really Make You Smarter?

Excellent update from Giulio Ruffini of Neuroelectrics. Full of links to relevant papers.

tDCS and Stroke: What We Know So Far (Jan 2013)

As far as I can tell, this is a new development in understanding the mechanism for the mediation of pain using tDCS.

Immediate effects of tDCS on the μ-opioid system of a chronic pain patient
To our knowledge, we provide data for the first time in vivo that there is possibly an instant increase of endogenous μ-opioid release during acute motor cortex neuromodulation with tDCS.
(And the pop-sci media follow-up Electrical Current Can Unlock The Seriously Good Drugs In Your Brain and Happiness Is a Warm Transcranial Direct Current Electrode)

A lot of research is going on right now into understanding where exactly, current if flowing.

The electric field in the cortex during transcranial current stimulation
The aim of this study was to investigate the effect of tissue heterogeneity and of the complex cortical geometry on the electric field distribution.

Some context.

A pioneer work on electric brain stimulation in psychotic patients. Rudolph Gottfried Arndt and his 1870s studies.
Today’s brain stimulation methods are commonly traced back historically to surgical brain operations. With this one-sided historical approach it is easy to overlook the fact that non-surgical electrical brain-stimulating applications preceded present-day therapies.

Mental Practice, or MP is practicing doing something without actually doing it. A musician imagining playing their instrument for instance. This study measured quality of handwriting with the non-dominant hand while using tDCS.

Site-specific effects of mental practice combined with transcranial direct current stimulation on motor learning
In conclusion, our results suggest that MP-induced effects in improving motor performance can be successfully consolidated by excitatory non-invasive brain stimulation on the M1 and left DLPFC.

Anodal transcranial direct current stimulation of prefrontal cortex enhances working memory – Springer

[Update 12/17/2012 Another paper discussing the efficacy of using tDCS to enhance working memory. Transcranial direct current stimulation of the prefrontal cortex modulates working memory performance: combined behavioural and electrophysiological evidence]

Working memory, as associated with ‘brain training’ and ‘plasticity‘, is often expressed as what one would wish to have more of, or at the very least, what one hopes not to lose as we age. (For a great overview of working memory and the how’s of enhancing it, see this fascinating post from neuroscientist Bradley Voytek’s blog  Working memory and cognitive enhancement.)

Our aim was to determine whether anodal transcranial direct current stimulation, which enhances brain cortical excitability and activity, would modify performance in a sequential-letter working memory task when administered to the dorsolateral prefrontal cortex DLPFC. Fifteen subjects underwent a three-back working memory task based on letters. This task was performed during sham and anodal stimulation applied over the left DLPFC. Moreover seven of these subjects performed the same task, but with inverse polarity cathodal stimulation of the left DLPFC and anodal stimulation of the primary motor cortex M1. Our results indicate that only anodal stimulation of the left prefrontal cortex, but not cathodal stimulation of left DLPFC or anodal stimulation of M1, increases the accuracy of the task performance when compared to sham stimulation of the same area. This accuracy enhancement during active stimulation cannot be accounted for by slowed responses, as response times were not changed by stimulation. Our results indicate that left prefrontal anodal stimulation leads to an enhancement of working memory performance. Furthermore, this effect depends on the stimulation polarity and is specific to the site of stimulation. This result may be helpful to develop future interventions aiming at clinical benefits.

via Anodal transcranial direct current stimulation of prefrontal cortex enhances working memory – Springer.
full pdf

This 2011 paper does confirm positive results of tDCS in a similar application and test setup. Improving working memory: exploring the effect of transcranial random noise stimulation and transcranial direct current stimulation on the dorsolateral prefrontal cortex.

However, the study does provide confirmation of previous findings that anodal tDCS enhances some aspects of DLPFC functioning.