Since the first reports of transcranial direct current stimulation (tDCS) by Priori et al. (1998)) and Nitsche and Paulus, 2000, Nitsche and Paulus, 2001), tDCS has been applied to many research issues because it can modulate the neural networks in the human brain painlessly and non-invasively (Priori et al., 1998, Nitsche and Paulus, 2000, Nitsche and Paulus, 2001). In other words, tDCS can induce neural plasticity (Ugawa, 2012). Most of its adverse effects are mild and disappear soon after stimulation, but several papers have reported that some adverse effects, most commonly skin problems, can persist even after stimulation. Recently, since the invention of transcranial alternating current stimulation (tACS) by Antal et al. (2008)), tACS has also been applied in research for the modulation of neural activity through the entrainment on brain oscillations (Antal et al., 2008, Antal and Herrmann, 2016). As in tDCS, the adverse effects of tACS are mild and disappear just after stimulation. Yet there have been far fewer papers on safety issues or adverse events of tACS as compared to tDCS. To date, there are no formal safety guidelines for the selection of stimulus parameters in either tDCS or tACS (Fertonani et al., 2015). Therefore, we aim to summarize the adverse events of tDCS and tACS in this review. At present, the safety and ethical issues of both stimulation techniques should be considered by each institution due to the lack of certainty about their risks. This review may provide some useful information for these considerations. In addition, this review is expected to be useful for the establishment of safety guidelines in the near future.
Posts Tagged Transcranial direct current stimulation (tDCS)
Transcranial direct current stimulation (tDCS) has been investigated over the years due to its short and also long-term effects on cortical excitability and neuroplasticity. Although its mechanisms to improve motor function are not fully understood, this technique has been suggested as an alternative therapeutic method for motor rehabilitation, especially those with motor function deficits. When applied to the primary motor cortex, tDCS has shown to improve motor function in healthy individuals, as well as in patients with neurological disorders. Based on its potential effects on motor recovery, identifying optimal targets for tDCS stimulation is essential to improve knowledge regarding neuromodulation as well as to advance the use of tDCS in clinical motor rehabilitation.
Methods and results
Therefore, this review discusses the existing evidence on the application of four different tDCS montages to promote and enhance motor rehabilitation: (1) anodal ipsilesional and cathodal contralesional primary motor cortex tDCS, (2) combination of central tDCS and peripheral electrical stimulation, (3) prefrontal tDCS montage and (4) cerebellar tDCS stimulation. Although there is a significant amount of data testing primary motor cortex tDCS for motor recovery, other targets and strategies have not been sufficiently tested. This review then presents the potential mechanisms and available evidence of these other tDCS strategies to promote motor recovery.
In spite of the large amount of data showing that tDCS is a promising adjuvant tool for motor rehabilitation, the diversity of parameters, associated with different characteristics of the clinical populations, has generated studies with heterogeneous methodologies and controversial results. The ideal montage for motor rehabilitation should be based on a patient-tailored approach that takes into account aspects related to the safety of the technique and the quality of the available evidence.
Transcranial Direct Current Stimulation (tDCS) is a non-invasive brain stimulation technique which delivers a constant electric current over the scalp to modulate cortical excitability [1,2,3]. Different montages of tDCS may induce diverse effects on brain networks, which are directly dependent on the electrodes positioning and polarity. While anodal tDCS is believed to enhance cortical excitability, cathodal tDCS diminishes the excitation of stimulated areas, and these electrodes montages define the polarity-specific effects of the stimulation [4,5,6]. Due to the effects of tDCS on modulating cortical excitability, especially when applied to the primary motor cortex , this method of brain stimulation has been intensively investigated for motor function improvement both in healthy subjects [7, 8] and in various neurological pathologies [9, 10]. Neurological conditions that may obtain benefits from the use of tDCS include Stroke [11,12,13,14], Parkinson’s disease , Multiple Sclerosis [16, 17], among others.
The mechanisms of action underlying the modulation of neuronal activity induced by tDCS are still not completely understood. However, studies have demonstrated that the electric current generated by tDCS interferes in the resting membrane potential of neuronal cells, which modulates spontaneous brain circuits activity [1,2,3]. Some studies have suggested that tDCS could have an effect on neuronal synapsis’ strength, altering the activity of NMDA and GABA receptors, thus triggering plasticity process, such as long-term potentiation (LTP) and long-term depression (LTD) [18, 19]. The long-term effects of tDCS are also thought to be associated to changes in protein synthesis and gene expression [20, 21]. Additionally, neuroimaging study showed blood flow changes following stimulation, which may be related to a direct effect of tDCS over blood flow, with an increase in oxygen supply on cortical areas and subsequent enhancement of neuronal excitability . Given these mechanisms, tDCS seems to be a potential valuable tool to stimulate brain activity and plasticity following a brain damage.
The advantages of using tDCS include its low cost, ease of application, and safety. To date, there is no evidence of severe adverse events following tDCS in healthy individuals, as well as in patients with neurological conditions, such as stroke [23, 24]. Among the potential side effects presented after this type of stimulation, the most common ones consist of burn sensation, itching, transient skin irritation, tingling under the electrode, headache, and low intensity discomfort . As serious and irreversible side effects have not been reported, tDCS is considered a relatively safe and tolerable strategy of non-invasive brain stimulation.
The modifications of physiological and clinical responses induced by tDCS are extremely variable, as this type of stimulation can induce both adaptive or maladaptive plastic changes, and a wide spectrum of tDCS parameters influence the effects of this technique. Electrodes combination, montage and shape can easily interfere in the enhancement or inhibition of cortical excitability [6, 26]. Other parameters that may influence these outcomes include current intensity, current flow direction, skin preparation, and stimulation intervals [3, 27, 28] . In addition, in clinical populations, the heterogeneity of the brain lesions can also influence the inconsistency in tDCS effects . Despite the goal of tDCS of modulating cortical areas by using different parameters, some studies have showed that, by altering cortical excitability, the electrical field could reach subcortical structures, such as basal ganglia, due to brain connections between cortical and subcortical areas [30,31,32,33]. This potential effect on deeper brain structure has supported the broad investigation of tDCS in various disorders, even if the cortical region under stimulating electrode is not directly linked to the neurological condition being investigated. Indeed, the current variable and moderate effect sizes from clinical tDCS studies in stroke encourage researchers to test alternative targets to promote motor recovery in this condition.
In this review, we discuss evidence on the application of four different tDCS montages to promote and enhance motor rehabilitation:  anodal tDCS ipsilateral and cathodal tDCS bilateral,  combination of central and peripheral stimulation,  prefrontal montage and  cerebellar stimulation.[…]
[Abstract] Effects of Electrical Stimulation in Tinnitus Patients: Conventional Versus High-Definition tDCS
Background. Contradictory results have been reported for transcranial direct current stimulation (tDCS) as treatment for tinnitus. The recently developed high-definition tDCS (HD tDCS) uses smaller electrodes to limit the excitation to the desired brain areas.
Objective. The current study consisted of a retrospective part and a prospective part, aiming to compare 2 tDCS electrode placements and to explore effects of HD tDCS by matched pairs analyses.
Methods. Two groups of 39 patients received tDCS of the dorsolateral prefrontal cortex (DLPFC) or tDCS of the right supraorbital–left temporal area (RSO-LTA). Therapeutic effects were assessed with the tinnitus functional index (TFI), a visual analogue scale (VAS) for tinnitus loudness, and the hyperacusis questionnaire (HQ) filled out at 3 visits: pretherapy, posttherapy, and follow-up. With a new group of patients and in a similar way, the effects of HD tDCS of the right DLPFC were assessed, with the tinnitus questionnaire (TQ) and the hospital anxiety and depression scale (HADS) added.
Results. TFI total scores improved significantly after both tDCS and HD tDCS (DLPFC: P < .01; RSO-LTA: P < .01; HD tDCS: P = .05). In 32% of the patients, we observed a clinically significant improvement in TFI. The 2 tDCS groups and the HD tDCS group showed no differences on the evolution of outcomes over time (TFI: P = .16; HQ: P = .85; VAS: P = .20).
Conclusions. TDCS and HD tDCS resulted in a clinically significant improvement in TFI in 32% of the patients, with the 3 stimulation positions having similar results. Future research should focus on long-term effects of electrical stimulation.
via Effects of Electrical Stimulation in Tinnitus Patients: Conventional Versus High-Definition tDCS – Laure Jacquemin, Giriraj Singh Shekhawat, Paul Van de Heyning, Griet Mertens, Erik Fransen, Vincent Van Rompaey, Vedat Topsakal, Julie Moyaert, Jolien Beyers, Annick Gilles, 2018
- No serious adverse effects have been reported in experiments using either tDCS or tACS.
- Persistent adverse effects of tDCS are mainly skin problems; for tACS, none have been reported.
- Further safety investigations are needed.
Transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS) have been applied to many research issues because these stimulation techniques can modulate neural activity in the human brain painlessly and non-invasively with weak electrical currents. However, there are no formal safety guidelines for the selection of stimulus parameters in either tDCS or tACS. As a means of gathering the information that is needed to produce safety guidelines, in this article, we summarize the adverse events of tDCS and tACS. In both stimulation techniques, most adverse effects are mild and disappear soon after stimulation. Nevertheless, several papers have reported that, in tDCS, some adverse events persist even after stimulation. The persistent events consist of skin lesions similar to burns, which can arise even in healthy subjects, and mania or hypomania in patients with depression. Recently, one paper reported a pediatric patient presenting with seizure after tDCS, although the causal relationship between stimulation and seizure is not clear. As this seizure is the only serious adverse events yet reported in connection with tDCS, tDCS is considered safe. In tACS, meanwhile, no persistent adverse events have been reported, but considerably fewer reports are available on the safety of tACS than on the safety of tDCS. Therefore, to establish the safety of tDCS and tACS, we need to scan the literature continuously for information on the adverse events of both stimulation techniques. Further safety investigations are also required.
…The non-invasive brain stimulation techniques of transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) have developed considerably over the last 25 years. Recent studies have used these techniques to enhance motor and cognitive function, modulate psychiatric symptoms, and reduce pain. Here, we briefly present TMS and tDCS techniques, discuss their safety, and provide examples of studies applying these interventions to enhance movement function following stroke. Though further studies are required, investigations so far provide important first steps in the use of non-invasive brain stimulation techniques to aid routine rehabilitation therapy. We discuss future directions for the field in terms of study development, choice of motor task, and target sites for stimulation…