When Size Matters: Large Electrodes Induce Greater Stimulation-related Cutaneous Discomfort Than Smaller Electrodes at Equivalent Current Density

Turi, Zsolt; Ambrus, Géza Gergely; Ho, Kerrie-Anne; Sengupta, Titas; Paulus, Walter; Antal, Andrea

doi:10.1016/j.brs.2014.01.059

Cited by 52 publications

(37 citation statements)

References 35 publications

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“…1A and Methods for details). Placebo intervention was delivered by an active sham protocol of tDCS (see Methods for details) that is insufficient to induce physiological changes in the brain, but capable of inducing substantial cutaneous sensations4647.…”

Section: Resultsmentioning

confidence: 99%

“…Beyond the primary physiological effects that constitute the main focus of most of the NIBS studies, the application of tDCS even at relatively low intensities (starting from about 0.4 mA) induces intensity- and electrode size-dependent cutaneous sensations, also known as the secondary induced effect of tDCS, which requires the use of an active sham control476061. The most frequently applied sham protocol for tDCS is the so called ‘fade-in, short stimulation, fade-out’ protocol46, which is thought to lack any physiological or behavioral after-effects due to the low stimulation intensity and short stimulation duration59.…”

Section: Discussionmentioning

confidence: 99%

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Placebo Intervention Enhances Reward Learning in Healthy Individuals

Turi

Mittner

Paulus

et al. 2017

Sci Rep

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According to the placebo-reward hypothesis, placebo is a reward-anticipation process that increases midbrain dopamine (DA) levels. Reward-based learning processes, such as reinforcement learning, involves a large part of the DA-ergic network that is also activated by the placebo intervention. Given the neurochemical overlap between placebo and reward learning, we investigated whether verbal instructions in conjunction with a placebo intervention are capable of enhancing reward learning in healthy individuals by using a monetary reward-based reinforcement-learning task. Placebo intervention was performed with non-invasive brain stimulation techniques. In a randomized, triple-blind, cross-over study we investigated this cognitive placebo effect in healthy individuals by manipulating the participants' perceived uncertainty about the intervention's efficacy. Volunteers in the purportedly low-and high-uncertainty conditions earned more money, responded more quickly and had a higher learning rate from monetary rewards relative to baseline. Participants in the purportedly highuncertainty conditions showed enhanced reward learning, and a model-free computational analysis revealed a higher learning rate from monetary rewards compared to the purportedly low-uncertainty and baseline conditions. Our results indicate that the placebo response is able to enhance reward learning in healthy individuals, opening up exciting avenues for future research in placebo effects on other cognitive functions.Observational and interventional approaches are concomitantly used to study brain networks and their putative contributions to certain brain functions 1 . While the former approach is necessary to characterize the spatiotemporal patterns of neural activity, the interventional approach constitutes an important step towards facilitating causal inference 2 . Non-invasive brain stimulation (NIBS) interventions offer the possibility to induce transient perturbations in intact human brain networks by using electromagnetic induction or electrical current, while minimizing possible health risks, financial costs and ethical concerns [3][4][5] . Transcranial direct current stimulation (tDCS) is the most frequently employed research tool in studies that use electrical current as a NIBS technique 3 . It passes constant, low intensity current between two or more electrodes attached to the intact scalp. Depending on the polarity, the externally applied constant current can increase or decrease the spontaneous firing rate (i.e., cortical excitability) of the stimulated brain regions by depolarizing or hyperpolarizing resting membrane potentials 3 . Although most of the commercially available and certified tDCS devices are equipped with a double-blind operation mode, a large number of studies still use a single-blind study design, no blinding at all or inadequate blinding 6 . In these cases, the impact of intentional and unconscious preferences, bias and expectations of the participants as well as of the researchers can possibly lead to an overestima...

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Placebo Intervention Enhances Reward Learning in Healthy Individuals

Turi

Mittner

Paulus

et al. 2017

Sci Rep

Self Cite

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“…Furthermore, it is important to note that current density (current intensity to electrode contact area) is not a good parameter to linearly extrapolate the magnitude of the generated electric fields 54 in the brain or levels of discomfort. 55 …”

Section: Discussionmentioning

confidence: 99%

Intensity Dependent Effects of Transcranial Direct Current Stimulation on Corticospinal Excitability in Chronic Spinal Cord Injury

Murray

Edwards

Ruffini

et al. 2015

Archives of Physical Medicine and Rehabilitation

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Objective To investigate the effects of anodal transcranial direct current stimulation (a-tDCS) intensity on corticospinal excitability and affected muscle activation in individuals with chronic spinal cord injury (SCI). Design Single blind, randomized, sham-controlled, crossover study. Setting Medical Research Institute and Rehabilitation Hospital. Participants Nine volunteers with chronic SCI and motor dysfunction in wrist extensor muscles. Intervention Three single session exposures to 20 minutes of a-tDCS (anode over the extensor carpi radialis (ECR) muscle representation on the left primary motor cortex, cathode over the right supraorbital area), using 1 mA, 2 mA or sham stimulation, delivered at rest, with at least one week between sessions. Outcome Measures Corticospinal excitability was assessed with motor evoked potentials (MEPs) from the ECR muscle using surface electromyography (EMG) following transcranial magnetic stimulation. Changes in spinal excitability, sensory threshold and muscle strength were also investigated. Results Mean MEP amplitude significantly increased by ~40% immediately following 2 mA a-tDCS (Pre 0.36±0.1 mV; Post 0.47±0.11 mV; p=0.001), but not with 1 mA or sham. Maximal voluntary EMG measures remained unaltered across all conditions. Sensory threshold significantly decreased over time following 1 mA (p=0.002) and 2 mA (p=0.039) a-tDCS, and did not change with sham. F-wave persistence showed a non-significant trend for increase (Pre: 32±12%; Post: 41±10%; Follow-up: 46±12%) following 2 mA stimulation. No adverse effects were reported with any of the experimental conditions. Conclusion Anodal-tDCS can transiently raise corticospinal excitability to affected muscles in chronic SCI patients following 2 mA stimulation. Sensory perception can improve with both 1 and 2 mA stimulation. This study gives support to the safe and effective use of a-tDCS using small electrodes in SCI patients, and highlights the importance of stimulation intensity.

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“…Contact dermatitis following tDCS has also been reported (Riedel et al, 2012). Contributing factors are electrode position, pre-existing conditions such as allergies to skin creams, extensive skin heating, high impedance (electrode dry or defect, solution salinity of electrode sponges and deterioration of the sponges, inappropriate contact solution, incorrect electrode fixation, non-uniform contact pressure of electrodes to skin), prolonged duration or repeated sessions, high current density (high current, small electrode) (Dundas et al, 2007; Frank et al, 2010; Guleyupoglu et al, 2014; McFadden et al, 2011; Norris et al, 2010; Palm et al, 2014, 2008a; Riedel et al, 2012; Rodriguez et al, 2014; Turi et al, 2014; Wang et al, 2015). …”

Section: The Application Of Low Intensity Tes In Human Studies: Aementioning

confidence: 99%

Low intensity transcranial electric stimulation: Safety, ethical, legal regulatory and application guidelines

Antal

Alekseichuk

Bikson

et al. 2017

Clinical Neurophysiology

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Low intensity transcranial electrical stimulation (TES) in humans, encompassing transcranial direct current (tDCS), transcutaneous spinal Direct Current Stimulation (tsDCS), transcranial alternating current (tACS), and transcranial random noise (tRNS) stimulation or their combinations, appears to be safe. No serious adverse events (SAEs) have been reported so far in over 18,000 sessions administered to healthy subjects, neurological and psychiatric patients, as summarized here. Moderate adverse events (AEs), as defined by the necessity to intervene, are rare, and include skin burns with tDCS due to suboptimal electrode-skin contact. Very rarely mania or hypomania was induced in patients with depression (11 documented cases), yet a causal relationship is difficult to prove because of the low incidence rate and limited numbers of subjects in controlled trials. Mild AEs (MAEs) include headache and fatigue following stimulation as well as prickling and burning sensations occurring during tDCS at peak-to-baseline intensities of 1–2 mA and during tACS at higher peak-to-peak intensities above 2 mA. The prevalence of published AEs is different in studies specifically assessing AEs vs. those not assessing them, being higher in the former. AEs are frequently reported by individuals receiving placebo stimulation. The profile of AEs in terms of frequency, magnitude and type is comparable in healthy and clinical populations, and this is also the case for more vulnerable populations, such as children, elderly persons, or pregnant women. Combined interventions (e.g., co-application of drugs, electrophysiological measurements, neuroimaging) were not associated with further safety issues. Safety is established for low-intensity ‘conventional’ TES defined as <4 mA, up to 60 min duration per day. Animal studies and modeling evidence indicate that brain injury could occur at predicted current densities in the brain of 6.3–13 A/m2 that are over an order of magnitude above those produced by tDCS in humans. Using AC stimulation fewer AEs were reported compared to DC. In specific paradigms with amplitudes of up to 10 mA, frequencies in the kHz range appear to be safe. In this paper we provide structured interviews and recommend their use in future controlled studies, in particular when trying to extend the parameters applied. We also discuss recent regulatory issues, reporting practices and ethical issues. These recommendations achieved consensus in a meeting, which took place in Göttingen, Germany, on September 6–7, 2016 and were refined thereafter by email correspondence.

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When Size Matters: Large Electrodes Induce Greater Stimulation-related Cutaneous Discomfort Than Smaller Electrodes at Equivalent Current Density

Cited by 52 publications

References 35 publications

Placebo Intervention Enhances Reward Learning in Healthy Individuals

Placebo Intervention Enhances Reward Learning in Healthy Individuals

Intensity Dependent Effects of Transcranial Direct Current Stimulation on Corticospinal Excitability in Chronic Spinal Cord Injury

Low intensity transcranial electric stimulation: Safety, ethical, legal regulatory and application guidelines

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