Cathodal tDCS produces sensation while anodal tDCS does not
the verdict
REFUTED
the evidence says no
refutedsupported
the weight of evidence
2 sources for · 1 against
The retrieved literature indicates that tDCS reliably causes mild cutaneous sensations such as tingling or itching, but comparative evaluations report no significant differences in sensation ratings between anodal and cathodal stimulation groups.
Transcranial direct current stimulation (tDCS) is a noninvasive method of brain modulation that is increasingly tested for the treatment of neuropsychiatric disorders (Murphy et al 2009) and cognitive enhancement (Paulus, 2004; Talelli and Rothwell, 2006). Conventional tDCS protocols apply 1–2 mA of current, for several minutes, through conductive-rubber electrodes inserted in sponge wrappers, which are typically soaked in saline, before being placed on the scalp. tDCS has many useful characteristics including low cost, ease of use, portability, and absence of significant side-effects. Indeed, during tDCS, mild tingling or itching sensation are the most common adverse effects (Poreisz et al., 2007), and though isolated cases of skin burns have been reported (Lagopoulos and Degabriele, 2008; Palm et al., 2008), relatively large scale experiences from several active centers, including at Gottingen, suggest that under proper protocols, significant adverse events are avoided (Dundas et al., 2007; Loo et al., 2010; Poreisz et al., 2007).
Acute sensation under electrodes during DC stimulation is well established (Leeming et al 1970, Mason and Mackay, 1976) and is highly dependent on both stimulation intensity and electrode design (Dundas et al., 2007; Forrester and Petrofsky, 2004); Martinsen et al., 2004; Minhas et al., 2010). Though generally increasing applied current increases all physiological responses, sensation does not simply correlate with either skin damage or brain modulation (Bikson et al., 2009) because of importance of electrode design and montage (for example increasing the proximity of electrodes decreases total brain but not skin current). None-the-less, sensation is clinically significant in itself for several reasons including tolerability (especially in vulnerable populations), confounding of experimental and clinical results, and blinding. The report in this edition by Ambrus and colleagues in Gottingen evaluated sensation differences for surface-area matched (35 cm2) rectangular and round electrodes. For anodal and cathodal tDCS, as well as tRNS, they found no substantial differences in detection threshold, detection rate, false-positive rate, or quality of sensation.
It is well established, including through computational modeling studies, that during electrical stimulation, current distribution at the electrode-tissue (skin) interface is not uniform, with high concentration of current density at the electrode edges (Miranda et al., 2006). The concentration of current density at an electrode edge is generally undesired for safety reasons (especially for implanted electrodes; (Merrill et al., 2005)) and may increase sensation during trancutaneous stimulation. Note that during transcranial electrical stimulation, subsequent current dispersion across deeper tissues results in no electrode-edge related current concentrations at the brain (Miranda et al., 2006, Datta et al., 2008, Datta et al., 2009a,b). Various strategies for normalizing current distribution at the electrode-tissue interface have been developed focusing on the materials and/or shape of the electrode (Krasteva and Papazov, 2002; Gilad et al., 2007; Minhas et al., 2010) - motivating the tDCS/tRNS electrode shape study by Ambrus et al (2010).
We modeled the current density at the electrode-skin interface under conditions approximating those tested by Ambrus et al. (2010). Consistent with previous results, for both rectangular and round electrodes, the current density was significantly higher at the electrode edges (Figure 1). For the same average current density (total current applied to equally sized electrodes), there was a moderately higher peak concentration of current for the rectangular electrodes than for the circular electrodes (Figure 1 a2, b3), but only at the rectangular electrode corners (Figure 1 a3, b3). Given the scale (peak) and nature (distribution) of these differences, it is not surprising that difference in sensation cou
Background and Objectives Motor learning experiments with transcranial direct current stimulation (tDCS) at 2mA have produced mixed results. We hypothesize that tDCS will boost motor learning provided sufficiently high field intensity on the motor cortex. Methods In a single-blinded, between-subject design, 72 healthy right-handed participants received either anodal or cathodal tDCS at 4mA while they learned to perform a sequence of key presses using their non-dominant hand for about 12 minutes. Cathodal stimulation served as an active control for sensation. A separate sham-stimulation group established baseline performance. Gains during practice and rest periods were analyzed (called micro-online and -offline learning). The target for stimulation was identified on the motor cortex using fMRI. After optimization with individual current flow models, we selected a single montage for all 108 participants with 4 frontal and 4 parietal electrodes each drawing 1mA. Results We found significant gains in performance with anodal stimulation (Cohen’s d=0.7). The boost in performance persisted for at least one hour. Subsequent learning for a new sequence and the opposite hand also improved. Concurrent tDCS enhanced micro-offline learning, while subsequent learning relied on micro-online gains. Sensation ratings were comparable in the active groups and did not exceed moderate levels. The new electrode montage achieved a better tradeoff between stimulation intensity and sensations on the scalp as compared to alternative montages. Conclusion The present paradigm shows reliable behavioral effects at 4mA and is well-tolerated. It may serve as a go-to experiment for future studies on motor learning and tDCS. Highlights tDCS resulted in a lasting boost of concurrent learning with effect size of Cohen’s d=0.7. Subsequent learning was also improved, indicating a form of meta-learning. Detailed analysis of behavior suggests an effect of tDCS on sequence consolidation. A novel electrode
Background and objectives: Motor learning experiments with transcranial direct current stimulation (tDCS) at 2 mA have produced mixed results. We hypothesize that tDCS boosts motor learning provided sufficiently high field intensity on the motor cortex. Methods: In a single-blinded design, 108 healthy participants received either anodal (N = 36) or cathodal (N = 36) tDCS at 4 mA total, or no stimulation (N = 36) while they practiced a 12-min sequence learning task. Anodal stimulation was delivered across four electrode pairs (1 mA each), with anodes above the right parietal lobe and cathodes above the right frontal lobe.
Cathodal stimulation, with reversed polarities, served as an active control for sensation, while the no-stimulation condition established baseline performance. fMRI-localized targets on the primary motor cortex in 10 subjects were used in current flow models to optimize electrode placement for maximal field intensity. A single electrode montage was then selected for all participants. Results: We found a significant difference in performance with anodal vs. cathodal stimulation (Cohen’s d = 0.71) and vs. no stimulation (d = 0.56). This effect persisted for at least 1 h, and subsequent learning for a new sequence and the opposite hand also improved.
Most but not all subjects were naive to tDCS and electrical stimulation. All subjects completed the full session of experimental procedures, even though they were allowed to withdraw due to discomfort at any point during the procedure. 2.3.2. Experimental design In a single-blind design, participants were randomly assigned to receive either anodal or cathodal stimulation (polarities as defined above; N = 36 per group). Anodal stimulation serves as the active, excitatory condition. Cathodal stimulation serves as the active control condition because at 4 mA the sensation is noticeable and cannot be reasonably shammed (see Fig. S7 ).
There was also a significant difference in learning of a new sequence S3 on the left hand between anodal and cathodal group 84 min after stimulation ( Fig. 5c ). The gain manifested in both number of correct sequences (U = 927, p = 1.7 × 10 −3 ) and tapping speed (t (70) = 2.3, p = 0.024, Fig. S1c ). 3.4. Anodal stimulation provided a net gain in performance over no stimulation The follow-up experiment on a third cohort tested a no-stimulation control group ( Fig. 6 ). The goal for this follow-up experiment was to test whether anodal stimulation improves performance over doing nothing at all, while acknowledging that sensation clearly differs to the active anodal and cathodal conditions.
Bayes Factor analysis shows that there were no significant differences in sensation ratings between the anodal and cathodal groups (BF01 = 2.59 in favor of no differences at the beginning of the trial), suggesting that the boost in learning seen in the anodal group is not the result of differing sensation. This is further supported by the lack of a performance difference between the cathodal and no-stimulation groups, despite a large difference in sensation. 3.7.
Discussion We find that anodal stimulation with inward current flow on M1 improves concurrent motor sequence learning with a medium to large effect size of 0.7 over cathodal stimulation with outward current flow. This effect outlasts the period of stimulation by at least 1 h. The active control condition ruled out the
Performance in the finger tapping task with concurrent tDCS targeting contralateral motor cortex. (a) The primary outcome, measured as the number of correct sequences completed per trial (mean: solid curve, SEM: shaded area). (b) The secondary outcome, measured as the tapping speed for each trial. * indicates significant difference (p < 0.05) between anodal and cathodal groups in the average over all trials. Fig. 5. Carry-over effects of stimulation on performance and learning. Number of correct sequences completed per trial during followup tasks, averaged across subjects.
This guideline summarizes updated safety data (2017-2025) and provides expert recommendations on the use of low intensity transcranial electrical stimulation (tES) in humans. tES encompasses several techniques including transcranial direct current stimulation (tDCS), oscillatory transcranial direct current stimulation (otDCS), transcranial alternating current stimulation (tACS), transcranial random noise stimulation (tRNS), transcranial temporal interference stimulation (tTIS), and their combinations or variations. Across over 300,000 sessions involving healthy individuals, patients with neuropsychiatric conditions, and other clinical populations, no tES-related serious adverse events (AEs) have been reported. Moderate AEs are rare and limited to a small range of specific applications. Mild AEs are common and include transient symptoms such as localized sensations (e.g., tingling or burning), headaches, and fatigue. Similar mild AEs are also reported by individuals receiving placebo stimulation. The frequency, magnitude, and type of AEs are comparable across healthy, clinical, and vulnerable groups, including children, elderly, or pregnant women. Combined interventions (e.g., co-application with EEG, TMS, or neuroimaging) have not shown increased safety risks. Safety is well-established for both bipolar and multichannel tES when applied up to 4 mA and up to 60 min per day. Higher intensities and longer stimulation durations may also be safe. Nevertheless, the number of studies using intensities above 4 mA or stimulating longer than 60 min is low. Home-based use of treatments is growing rapidly, leveraging remote supervision to provide patients with greater access and enable repeated, sustained dosing paradigms. We recommend using screening and AE questionnaires in future controlled studies, in particular when planning to extend the stimulation parameters applied. We discuss recent regulatory and ethical issues.
Effects vary by species, disease model, timing, and stimulation parameters. For example, anodal tDCS (4 kC/m 2 ) down-regulates hippocampal inflammatory mediators in a chronic pain model (Spezia Adachi et al., 2012), but upregulates them by both cathodal and anodal tDCS of the same charge density in cortical tissue in a rat epilepsy model (Regner et al., 2020). In post-stroke rodent model, cathodal tDCS (~66 kC/m 2 ) reduces microglial activation and immune cell invasion (Peruzzotti-Jametti et al., 2013) and induces a shift in microglia polarization ( Braun et al., 2016 ), while dual-tDCS down-regulates inflammatory mediators in cortex and hippocampus ( Huang et al., 2021 ).
The term “return” electrodes does not mean an electrode is inert but rather reflects the hypothesis that it plays a less critical role in the targeted outcome. Notably, the return electrode can be either the anode or cathode, depending on the montage and the intended direction of current flow. Similarly, designations like “anodal tDCS” or “cathodal tDCS” highlight the presumed functional importance of the anode or cathode, respectively, within a given protocol ( Bikson et al., 2019 ).
With multi electrode montages, it is also possible to provide higher total current by splitting current to individual electrodes ( Harrie et al., 2023 ). Electrode design plays a fundamental role in tolerability. While for any given current, decreasing electrode size will proportionally increase current density; electrode materials have a more important role in tolerability. For example, well-designed HD electrodes produce higher current density than conventional tDCS pad electrodes without necessarily enhancing skin sensation ( Reckow et al., 2018 ; Turski et al., 2017 ). Electrode shape appears to have minimal effect on the resulting sensation ( Ambrus et al., 2011 ; Minhas et al., 2011 ).
This means that the current oscillates at a specific frequency while for each electrode remaining entirely within either the positive or negative polarity range (i.e., either anodal or cathodal) and intensity within the standard range (i.e., between 1 and 2 mA). Given that otDCS incorporates elements of both tDCS and tACS, its safety profile may be expected to be similar to those of these established techniques. A recent study compared the subjective experience (tolerability) and SEs of tDCS (1.5 mA), tACS (0 ± 1 mA, i.e., 2 mA peak-to-peak), and otDCS (1.5 ± 0.5 mA, i.e., between 1 and 2 mA) in healthy young adults ( Bjekić et al., 2024 ).
The findings indicated that otDCS induced discomfort levels comparable to tDCS while producing similarly mild but somewhat less frequent AEs, including scalp itching (31.0 % post-tDCS, 26.2 % post-otDCS), tingling sensations (42.9 % post-tDCS, 23.8 % post-otDCS), and mild scalp irritation (28.6 % post-tDCS, 16.7 % post-otDCS). SEs typically associated with alternating currents, such as phosphenes, were reported by three participants during tACS and one during otDCS, while shaking of the visual field was
Importantly, while most studies report only mild, transient effects (e.g., tingling, itching, redness), comparable to those observed with oncedaily protocols, a trial of 29 patients with depression receiving 50 tDCS sessions (five per day, 20 min duration at 2 mA, 20 min inter session interval with left anodal/right cathodal DLPFC stimulation) found that 18 (62 %) developed mild, persistent erythematous-squamous plaques under the anode, consistent with irritative contact dermatitis ( Miron et al., 2023 ). Additionally, they reported high rates of redness at electrodes sites (100 %), headaches (67.9 %) and fatigue (57.1 %).
A study of 11 patients with mild cognitive impairment (MCI), who received 2 mA tDCS for 20 min per day over 5 consecutive days (55 sessions in total), reported a pricking sensation (n = 30, 55 %) and a mild burning sensation (n = 8, 14 %) as the most common AEs; no AE was reported in 15 sessions (31 %), while all reported AEs were of mild intensity ( Murugaraja et al., 2017 ).
Everything we examined (3)
This check searched the claim as stated. It did not run a separate search for evidence against it.