Repeated sessions of transcranial direct current stimulation for treatment of chronic subjective tinnitus: a pilot randomized controlled trial

Subjective tinnitus is an auditory phantom sensation characterized by the perception of sound in the absence of an identifiable external source. This distressing audiological symptom can severely affect the quality of life. Transcranial direct current stimulation (tDCS) is a noninvasive technique that can induce short-term relief in tinnitus in some patients. The purpose of this pilot double-blind randomized controlled trial was to investigate whether repeated application of anodal tDCS over left temporoparietal area could induce long-lasting relief in patients with chronic tinnitus. Twenty-two patients with chronic tinnitus for at least 6 months were randomly allocated into two groups and received five sessions of anodal (N = 11) or sham (N = 11) stimulation in five consecutive days. A current intensity of 2 mA for 20 min was used for anodal stimulation. Outcomes were assessed using Persian version of tinnitus handicap inventory (THI), loudness and distress visual analog scale (VAS) scores and clinical global impression (CGI) scale. The trial is registered at the Iranian Registry of Clinical Trials (IRCT) with the reference ID of IRCT2014082018871N1. No statistically significant difference was found between anodal and sham stimulation regarding either immediate or long-lasting effects over the 2 weeks follow-up period. Deterioration of symptoms and alteration in tinnitus characteristics were reported by a few patients. There were no significant long-term beneficial effects following tDCS of the left temporoparietal area.     

Safety of repeated sessions of transcranial direct current stimulation: A systematic review

Background

Repeated sessions of transcranial direct current stimulation (tDCS) are increasingly used for therapeutic applications. However, adverse events (AEs) associated with repeated sessions have not been comprehensively evaluated.

Transient tinnitus suppression induced by repetitive transcranial magnetic stimulation and transcranial direct current stimulation

Modulation of activity in the left temporoparietal area (LTA) by 10 Hz repetitive transcranial magnetic stimulation (rTMS) results in a transient reduction of tinnitus. We aimed to replicate these results and test whether transcranial direct current stimulation (tDCS) of LTA could yield similar effect. Patients with tinnitus underwent six different types of stimulation in a random order: 10-Hz rTMS of LTA, 10-Hz rTMS of mesial parietal cortex, sham rTMS, anodal tDCS of LTA, cathodal tDCS of LTA and sham tDCS. A non-parametric analysis of variance showed a significant main effect of type of stimulation ( P  = 0.002) and post hoc tests showed that 10-Hz rTMS and anodal tDCS of LTA resulted in a significant reduction of tinnitus. These effects were short lasting. These results replicate the findings of the previous study and, in addition, show preliminary evidence that anodal tDCS of LTA induces a similar transient tinnitus reduction as high-frequency rTMS.     

Immediate memory and electrophysiologic effects of prefrontal cortex transcranial direct current stimulation on neurotypical individuals and individuals with chronic traumatic brain injury: a pilot study

Purpose/aim: Memory impairment post-TBI is common, frequently persistent, and functionally debilitating. The purposes of this pilot study were to assess and to compare immediate behavioral auditory working memory and electrophysiologic effects of three different, randomized, conditions of left dorsolateral prefrontal cortex (LDLPFC) transcranial direct current stimulation (tDCS) applied to four neurotypical adults and four adults with chronic traumatic brain injury (TBI). Materials/methods: Pre- and post-anodal, cathodal, and sham tDCS auditory memory performance, auditory event-related potentials (P300 amplitude and latency) and power of alpha and theta EEG bands were measured across individuals in each group. Results: Post-anodal tDCS only, the neurotypical and TBI groups both demonstrated significantly improved immediate auditory memory function. Also post-anodal tDCS, the TBI group demonstrated significantly increased P300 amplitude versus post-sham tDCS. The neurotypical group demonstrated no pre- post-tDCS electrophysiologic changes across conditions. Conclusions: These findings are consistent with findings of other studies of immediate tDCS effects on other types of memory in neurotypical individuals and in individuals with Parkinson's disease, Alzheimer's disease and stroke and suggest that individuals with memory impairments second to chronic TBI may benefit from LDLPFC anodal tDCS. Pairing tDCS with traditional behavioral memory interventions may facilitate TBI rehabilitation outcomes and warrants continued investigation.     

Short- and long-lasting tinnitus relief induced by transcranial direct current stimulation

A significant proportion of the population suffers from tinnitus, a bothersome auditory phantom perception that can severely alter the quality of life. Numerous experimental studies suggests that a maladaptive plasticity of the auditory and limbic cortical areas may underlie tinnitus. Accordingly, repetitive transcranial magnetic stimulation (rTMS) has been repeatedly used with success to reduce tinnitus intensity. The potential of transcranial direct current stimulation (tDCS), another promising method of noninvasive brain stimulation, to relieve tinnitus has not been explored systematically. In a double-blind, placebo-controlled and balanced order design, 20 patients suffering from chronic untreatable tinnitus were submitted to 20 minutes of 1 mA anodal, cathodal and sham tDCS targeting the left temporoparietal area. The primary outcome measure was a change in tinnitus intensity or discomfort assessed with a Visual Analogic Scale (VAS) change-scale immediately after tDCS and 1 hour later. Compared to sham tDCS, anodal tDCS significantly reduced tinnitus intensity immediately after stimulation; whereas cathodal tDCS failed to do so. The variances of the tinnitus intensity and discomfort VAS change-scales increased dramatically after anodal and cathodal tDCS, whereas they remained virtually unchanged after sham tDCS. Moreover, several patients unexpectedly reported longer-lasting effects (at least several days) such as tinnitus improvement, worsening, or changes in tinnitus features, more frequently after real than sham tDCS. Anodal tDCS is a promising therapeutic tool for modulating tinnitus perception. Moreover, both anodal and cathodal tDCS seem able to alter tinnitus perception and could, thus, be used to trigger plastic changes.     

Effect of prefrontal transcranial direct current stimulation on sexual arousal: A proof of concept study

There is preliminary evidence that high-frequency repetitive transcranial magnetic stimulation targeting the right dorsolateral prefrontal cortex (DLPFC) could reduce cue-induced sexual arousal. Here, we aimed to replicate this finding by using transcranial direct current stimulation (tDCS). In a randomized, double-blind, sham-controlled crossover study design, 24 healthy male participants received anodal tDCS over right DLPFC, anodal tDCS over left DLPFC, and sham tDCS with exposure to neutral and sexual video cues before and after each intervention. None of the interventions significantly reduced subjective sexual arousal. Stimulation parameters should be varied in further studies to identify factors relevant to the intended effect.     

Bifrontal transcranial direct current stimulation modulates tinnitus intensity and tinnitus-distress-related brain activity

Bifrontal transcranial direct current stimulation (tDCS), with the anodal electrode overlying the right and the cathodal electrode overlying the left dorsolateral prefrontal cortex, has been shown to suppress tinnitus significantly in 30% of patients. The source localized resting‐state electrical activity is recorded before and after bifrontal tDCS in patients who respond to tDCS to unravel the mechanism by which tDCS suppresses tinnitus. The present electroencephalography study (N = 12) provides support for the ability of bifrontal tDCS to suppress tinnitus intensity and tinnitus‐related distress by modulation of the pregenual anterior cingulate cortex, parahippocampal area and right primary auditory cortex in resting‐state spontaneous brain activity. These findings provide direct support for tDCS having an impact not only directly on the underlying dorsolateral prefrontal cortex but also indirectly on functionally connected brain areas relevant for tinnitus distress and tinnitus intensity, respectively.     

Effects on pain and cognition of transcranial direct current stimulation over the dorsolateral prefrontal cortex in women with chronic migraine

We compared the effects of one versus two daily sessions of anodal transcranial direct current stimulation (a-tDCS) delivered to the left dorsolateral prefrontal cortex (DLPFC) for 10 days in a cohort of 30 women (mean age 28.0±6.92) with chronic migraine (CM, disease duration: 37.8±48.41 month). Participants were randomly allocated to three groups: a-tDCS 1-s Group received one daily a-tDCS session; a-tDCS 2-s Group received two daily a-tDCS sessions; Group SHAM received one daily session with a simulated (placebo) current. All participants were assessed before, after and one month after treatment, using the Migraine Disability Assessment, Montreal Cognitive Assessment, d2 Test of Attention, Trail Making Test (part B), Sequence of Letters and Numbers of the Wechsler Adult Intelligence Scale – III, and Nine Hole Peg Test. We found no difference between groups in the cognitive measures and motor dexterity. However, after treatment, a significant decrease in migraine-related disability was found for the a-tDCS 1-s Group. For all variables, no cumulative effects were observed in a-tDCS 2-s compared to the a-tDCS 1-s Group. The study findings provide preliminary results for future clinical trials designed to compare different intervals between tDCS sessions in CM.     

Treatment of depression with transcranial direct current stimulation (tDCS): A Review

Major Depression Disorder (MDD) is usually accompanied by alterations of cortical activity and excitability, especially in prefrontal areas. These are reflections of a dysfunction in a distributed cortico-subcortical, bihemispheric network. Therefore it is reasonable to hypothesize that altering this pathological state with techniques of brain stimulation may offer a therapeutic target. Besides repetitive transcranial magnetic stimulation, tonic stimulation with weak direct currents (tDCS) modulates cortical excitability for hours after the end of stimulation, thus, it is a promising non-invasive therapeutic option. Early studies from the 1960s suggested some efficacy of DC stimulation to reduce symptoms in depression, but mixed results and development of psychotropic drugs resulted in an early abandonment of this technique. In the last years tDCS protocols have been optimized. Application of the newly developed stimulation protocols in patients with major depression has shown promise in few pilot studies. Further studies are needed to identify the optimal parameters of stimulation and the clinical and patient characteristics that may condition response to tDCS.     

Cerebellar transcranial direct current stimulation in children with ataxic cerebral palsy: A sham-controlled,crossover, pilot study

Objective: The aim of the present study was to analyze the use of anodal tDCS of the cerebellar region combined with treadmill training to improve balance and functional performance in children with ataxic cerebral palsy. Design: Single-blind, sham-controlled, crossover, pilot study. Setting: Rehabilitation center and research motion analysis laboratory. Participants: Children (N = 6) with ataxic cerebral palsy and balance deficit. Main Outcome Measures: Static balance (oscillations of the center of pressure), functional balance (Pediatric Balance Scale) and functional performance (Pediatric Evaluation of Disability Inventory) were evaluated. Results: Significant reductions occurred in oscillations of the center of pressure with eyes closed after active anodal tDCS only. The effects of treadmill training on functional balance and functional performance in mobility were maintained in the active tDCS group only. Conclusion: These preliminary data support the notion that anodal tDCS of the cerebellar region combined with treadmill training improves balance in children with ataxic cerebral palsy.     

Modulating affective experience and emotional intelligence with loving kindness meditation and transcranial direct current stimulation: A pilot study

Positive emotional perceptions and healthy emotional intelligence (EI) are important for social functioning. In this study, we investigated whether loving kindness meditation (LKM) combined with anodal transcranial direct current stimulation (tDCS) would facilitate improvements in EI and changes in affective experience of visual stimuli. LKM has been shown to increase positive emotional experiences and we hypothesized that tDCS could enhance these effects. Eighty-seven undergraduates were randomly assigned to 30 minutes of LKM or a relaxation control recording with anodal tDCS applied to the left dorsolateral prefrontal cortex (left dlPFC) or right temporoparietal junction (right TPJ) at 0.1 or 2.0 milliamps. The primary outcomes were self-reported affect ratings of images from the International Affective Picture System and EI as measured by the Mayer, Salovey and Caruso Emotional Intelligence Test. Results indicated no effects of training on EI, and no main effects of LKM, electrode placement, or tDCS current strength on affect ratings. There was a significant interaction of electrode placement by meditation condition (p = 0.001), such that those assigned to LKM and right TPJ tDCS, regardless of current strength, rated neutral and positive images more positively after training. Results suggest that LKM may enhance positive affective experience.     

Improving working memory: Exploring the effect of transcranial random noise stimulation and transcranial direct current stimulation on the dorsolateral prefrontal cortex

Objective

The aim of this study was to determine if working memory (WM) performance is significantly improved after the delivery of transcranial random noise stimulation (tRNS) to the left dorsolateral prefrontal cortex (DLPFC), compared to an active comparator or sham.

Methods

Ten participants undertook three experimental sessions in which they received 10 min of anodal tDCS (active comparator), tRNS or sham tDCS whilst performing the Sternberg WM task. Intra-stimulation engagement in a WM task was undertaken as this has been previously shown to enhance the effects of tDCS. Experimental sessions were separated by a minimum of 1 week. Immediately prior to and after each stimulation session the participants were measured on speed and accuracy of performance on an n-back task.

Results

There was significant improvement in speed of performance following anodal tDCS on the 2-back WM task; this was the only significant finding.

Conclusions

The results do not provide support for the hypothesis that tRNS improves WM. However, the study does provide confirmation of previous findings that anodal tDCS enhances some aspects of DLPFC functioning. Methodological limitations that may have contributed to the lack of significant findings following tRNS are discussed.

Significance

Anodal tDCS may have significant implications for WM remediation in psychiatric conditions, particularly schizophrenia.