High-definition transcranial direct current stimulation of the dorsolateral prefrontal cortex for tinnitus modulation: a preliminary trial

Neuromodulation Treatments Targeting Pathological Synchrony for Tinnitus in Adults: A Systematic Review

(1) Background: Tinnitus involves the conscious awareness of a tonal or composite noise for which there is no identifiable corresponding external acoustic source. For many people, tinnitus is a disorder associated with symptoms of emotional distress, cognitive dysfunction, autonomic arousal, behavioural changes, and functional disability. Many symptoms can be addressed effectively using education or cognitive behavioural therapy. However, there is no treatment that effectively reduces or alters tinnitus-related neurophysiological activity and thus the tinnitus percept. In this systematic review, we evaluated the effectiveness of neuromodulation therapies for tinnitus that explicitly target pathological synchronous neural activity. (2) Methods: Multiple databases were searched for randomised controlled trials of neuromodulation interventions for tinnitus in adults, with 24 trials included. The risk of bias was assessed, and where appropriate, meta-analyses were performed. (3) Results: Few trials used acoustic, vagal nerve, or transcranial alternating current stimulation, or bimodal stimulation techniques, with limited evidence of neuromodulation or clinical effectiveness. Multiple trials of transcranial direct current stimulation (tDCS) were identified, and a synthesis demonstrated a significant improvement in tinnitus symptom severity in favour of tDCS versus control, although heterogeneity was high. (4) Discussion: Neuromodulation for tinnitus is an emerging but promising field. Electrical stimulation techniques are particularly interesting, given recent advances in current flow modelling that can be applied to future studies.

Conceptual framework for tinnitus: a cognitive model in practice

Tinnitus is a conscious attended awareness perception of sourceless sound. Widespread theoretical and evidence-based neurofunctional and psychological models have tried to explain tinnitus-related distress considering the influence of psychological and cognitive factors. However, tinnitus models seem to be less focused on causality, thereby easily misleading interpretations. Also, they may be incapable of individualization. This study proposes a Conceptual Cognitive Framework (CCF) providing insight into cognitive mechanisms involved in the predisposition, precipitation, and perpetuation of tinnitus and consequent cognitive-emotional disturbances. The current CCF for tinnitus relies on evaluative conditional learning and appraisal, generating negative valence (emotional value) and arousal (cognitive value) to annoyance, distress, and distorted perception. The suggested methodology is well-defined, reproducible, and accessible, which can help foster future high-quality clinical databases. Perceived tinnitus through the perpetual-learning process can always lead to annoyance, but only in the clinical stage directly cause annoyance. In the clinical stage, tinnitus perception can lead indirectly to distress only with experiencing annoyance either with ("I n d - 1 C " = 1.87; 95% CI 1.18-2.72)["1st indirect path in the Clinical stage model": Tinnitus Loudness → Attention Bias → Cognitive-Emotional Value → Annoyance → Clinical Distress]or without ("I n d - 2 C "= 2.03; 95% CI 1.02-3.32)[ "2nd indirect path in the Clinical stage model": Tinnitus Loudness → Annoyance → Clinical Distress] the perpetual-learning process. Further real-life testing of the CCF is expected to express a meticulous, decision-supporting platform for cognitive rehabilitation and clinical interventions. Furthermore, the suggested methodology offers a reliable platform for CCF development in other cognitive impairments and supports the causal clinical data models. It may also enhance our knowledge of psychological disorders and complicated comorbidities by supporting the design of different rehabilitation interventions and comprehensive frameworks in line with the "preventive medicine" policy.

State of the art: non-invasive electrical stimulation for the treatment of chronic tinnitus

Subjective tinnitus is the perception of sound in the absence of external stimulation. Neuromodulation is a novel method with promising properties for application in tinnitus management. This study sought to review the types of non-invasive electrical stimulation in tinnitus to provide the foothold for further research. PubMed, EMBASE, and Cochrane databases were searched for studies on the modulation of tinnitus by non-invasive electrical stimulation. Among the four forms of non-invasive electrical modulation, transcranial direct current stimulation, transcranial random noise stimulation, and transauricular vagus nerve stimulation yielded promising results, whereas the effect of transcranial alternating current stimulation in the treatment of tinnitus has not been confirmed. Non-invasive electrical stimulation can effectively suppress tinnitus perception in some patients. However, the heterogeneity in parameter settings leads to scattered and poorly replicated findings. Further high-quality studies are needed to identify optimal parameters to develop more acceptable protocols for tinnitus modulation.

Dual-site transcranial direct current stimulation to treat tinnitus: a randomized controlled trial

Transcranial direct current stimulation (tDCS) has been proposed as a potential intervention for subjective tinnitus, but supporting evidence remains limited. We aimed to investigate the effect of anodal high-definition tDCS of the left temporal area and right dorsolateral prefrontal cortex on tinnitus severity. This double-blind randomized controlled trial included 77 patients (age range 18-79, 43 male) with chronic subjective tinnitus as their primary complaint. Thirty-eight subjects received six consecutive sessions of dual-site sequential high-definition-tDCS with electrodes positioned over the left temporal area and right dorsolateral prefrontal cortex. Both areas were stimulated for 15 min per session, with total stimulation time amounting to 30 min. Thirty-nine subjects received sham stimulation. The primary outcome measure was the change in tinnitus severity, as evaluated by the Tinnitus Functional Index, from baseline to a follow-up visit at 8 ± 2 weeks after treatment completion. Secondary outcomes included changes in perceived tinnitus loudness, as measured with a visual analogue scale and a tinnitus matching procedure, as well as scores on the Hospital Anxiety and Depression Scale, and the Hyperacusis Questionnaire. No differences in Tinnitus Functional Index change scores were identified between the active treatment and sham control groups (linear regression: P = 0.86). The Tinnitus Functional Index scores decreased significantly over time in both groups (P = 0.0012), indicating the presence of a considerable placebo effect. These change scores were significantly influenced by sex (linear regression: P = 0.037) and baseline symptoms of anxiety (linear regression: P = 0.049) in both groups. In general, Tinnitus Functional Index scores decreased more profoundly in males and in subjects with a higher degree of anxiety at baseline. None of the included secondary measures differed significantly between experimental arms. Our results suggest that dual-site sequential high-definition-tDCS of the left temporal area and right dorsolateral prefrontal cortex does not alleviate tinnitus severity. Interestingly, in our study population, fluctuations in tinnitus severity were influenced by gender and concurrent mental condition. It is therefore important to take these factors into account when conducting or planning randomized controlled trials in tinnitus populations.

Functional Connectivity Increases in Response to High-Definition Transcranial Direct Current Stimulation in Patients with Chronic Disorder of Consciousness

Highlights

Functional connectivity induced by HD-tDCS in DLPFC has different trends in CRS-R score improvers and non-improvers.

An increase in theta PLV in the left frontal–parietooccipital region was significantly associated with CRS-R changes.

DOC patients with increased PLV of the alpha band in the intra-bifrontal region have a better prognosis than those without.

Abstract

High-definition transcranial direct current stimulation (HD-tDCS) has been shown to play an important role in improving consciousness in patients with disorders of consciousness (DOCs), but its neuroelectrophysiological evidence is still lacking. To better explain the electrophysiological mechanisms of the effects of HD-tDCS on patients with DOCs, 22 DOC patients underwent 10 anodal HD-tDCS sessions of the left dorsolateral prefrontal cortex (DLPFC). This study used the Coma Recovery Scale-Revised (CRS-R) to assess the level of consciousness in DOC patients. According to whether the CRS-R score increased before and after stimulation, DOC patients were divided into a responsive group and a non-responsive group. By comparing the differences in resting-state EEG functional connectivity between different frequency bands and brain regions, as well as the relationship between functional connectivity values and clinical scores, the electrophysiological mechanism of the clinical effects of HD-tDCS was further explored. The change of the phase locking value (PLV) on the theta frequency band in the left frontal–parietooccipital region was positively correlated with the change in the CRS-R scores. As the number of interventions increased, we observed that in the responsive group, the change in PLV showed an upward trend, and the increase in the PLV appeared in the left frontal–parietooccipital region at 4–8 Hz and in the intra-bifrontal region at 8–13 Hz. In the non-responsive group, although the CRS-R scores did not change after stimulation, the PLV showed a downward trend, and the decrease in the PLV appeared in the intra-bifrontal region at 8–13 Hz. In addition, at the three-month follow-up, patients with increased PLV in the intra-bifrontal region at 8–13 Hz after repeated HD-tDCS stimulation had better outcomes than those without. Repeated anodal stimulation of the left DLPFC with HD-tDCS resulted in improved consciousness in some patients with DOCs. The increase in functional connectivity in the brain regions may be associated with the improvement of related awareness after HD-tDCS and may be a predictor of better long-term outcomes.

Effect of transcranial Direct Current Stimulation for tinnitus treatment: A systematic review and meta-analysis

OBJECTIVES

To evaluate the effect of tDCS on tinnitus distress, loudness and psychiatric symptoms.

METHODS

A systematic literature search of PubMed, Web of Science, Cochrane Library, VHL, EMBASE, PsycINFO, OVID, and CINAHL databases was carried out on articles published until July 2021. Inclusion criteria were published controlled trials using tDCS intervention with tinnitus patients, using a sham/control group, and measuring tinnitus loudness, distress and/or psychiatric symptoms. A meta-analysis was performed for the overall effect as well as to compare subgroups according to tDCS target (left temporoparietal area (LTA) and dorsolateral prefrontal cortex (DLPFC)).

RESULTS

Fourteen articles with 1031 participants were included. Six studies applied tDCS over the DLPFC, six over the LTA and two over both areas. Although the overall meta-analysis showed that tDCS significantly decreased tinnitus loudness (SMD=-0.35; 95%CI=-0.62 to -0.08, p = 0.01) and distress (SMD=-0.50, 95%CI=-0.91 to -0.10, p = 0.02).The subgroup analysis showed a significant effect only for tDCS over LTA for loudness (SMD=-0.46, 95%CI=-0.80 to -0.12, p = 0.009), and no other area resulted in significant change. There was no significant effect of treatment on psychiatric symptoms.

CONCLUSION

tDCS may improve tinnitus loudness and distress with a small to moderate effect size. Despite the overall positive effect, only LTA tDCS yielded a significant effect. Further well-controlled studies with larger sample sizes and broader exploration of tDCS montages and doses are warranted.

Adjuvant High-Definition Transcranial Direct Current Stimulation for Negative Symptoms in Schizophrenia: A Pilot Study

OBJECTIVE

In schizophrenia, negative symptoms account for a substantial amount of the comorbidity resulting in poor performance in social interaction, interpersonal relationships, economic functioning, and recreational activities. Research has implicated hypofrontality in the pathogenesis of negative symptoms of schizophrenia. Conventional transcranial direct current stimulation (tDCS) to the dorsolateral prefrontal cortex has attracted significant interest as an add-on treatment for negative symptoms in schizophrenia. High-definition tDCS (HD-tDCS), an optimized form of tDCS, has the potential for more focalized neuromodulation. Hence, we aimed to evaluate the efficacy of HD-tDCS over the left dorsolateral prefrontal cortex in the improvement of negative symptoms in schizophrenia.

METHODS

Fourteen patients with schizophrenia with predominantly negative symptoms were enrolled for this pilot, randomized, sham-controlled, double-blind trial. Each participant received 10 sessions of HD-tDCS at 2 mA for 20 minutes twice daily over 5 days. Negative symptoms were assessed with the Scale for Assessment of Negative Symptoms and Positive and Negative Syndrome Scale for Schizophrenia. The Calgary Depression Scale for Schizophrenia was used to rule out depressive symptoms. Assessments were carried out at baseline and at 2 weeks.

RESULTS

The improvement in negative symptoms in the active group was statistically significant at P value of 0.05 as compared with the sham group.

CONCLUSION

These results suggest that HD-tDCS may lead to improvement in negative symptoms of schizophrenia. Its use as an adjunct to pharmacological treatment of negative symptoms may be worth considering.

Survey of tinnitus patients' acceptance of high-definition transcranial direct current stimulation as a management option

OBJECTIVES

To investigate acceptance of high-definition transcranial direct current stimulation (HD-tDCS) as a management option for tinnitus.

DESIGN

Participants completed an online version of the Tinnitus Functional Index (TFI), after which they recorded their satisfaction ratings with different hypothetical intervention outcomes on a 10-point rating scale using Opinio survey software.

STUDY SAMPLE

Data from 272 tinnitus sufferers from English-speaking regions worldwide were collected, of which the majority had moderate to severe tinnitus as per TFI.

RESULTS

The survey showed that HD-tDCS was considered an acceptable form of tinnitus management, and that the satisfaction rating depended significantly on a number of factors: (1) the strength of the tinnitus reduction following the intervention (p < 0.001); 2) the duration of the intervention (p < 0.001); and (3) the effects of the intervention on either tinnitus loudness or tinnitus-related distress (p < 0.001). Respondents rated their satisfaction with the intervention 10/10 only if it completely eliminated tinnitus loudness, although reductions of 50-80% were also rated highly acceptable. No association was found between tinnitus severity and acceptability ratings.

CONCLUSIONS

These findings are important for future HD-tDCS trials for tinnitus, as they demonstrate the need to optimise stimulation protocols to increase effect sizes and decrease time spent on the treatment.

High Definition transcranial Direct Current Stimulation (HD-tDCS) for chronic tinnitus: Outcomes from a prospective longitudinal large cohort study

BACKGROUND

Transcranial Direct Current Stimulation (tDCS) aims to induce cortical plasticity by modulating the activity of brain structures. The broad stimulation pattern, which is one of the main limitations of tDCS, can be overcome with the recently developed technique called High-Definition tDCS (HD-tDCS).

OBJECTIVE

Investigation of the effect of HD-tDCS on tinnitus in a large patient cohort.

METHODS

This prospective study included 117 patients with chronic, subjective, non-pulsatile tinnitus who received six sessions of anodal HD-tDCS of the right Dorsolateral Prefrontal Cortex (DLPFC). Therapy effects were assessed by use of a set of standardized tinnitus questionnaires filled out at the pre-therapy (T_pre), post-therapy (T_3w) and follow-up visit (T_10w). Besides collecting the questionnaire data, the perceived effect (i.e., self-report) was also documented at T_10w.

RESULTS

The Tinnitus Functional Index (TFI) and Tinnitus Questionnaire (TQ) total scores improved significantly over time (p_TFI<0.01; p_TQ<0.01), with the following significant post hoc comparisons: T_pre vs. T_10w (p_TFI<0.05; p_TQ<0.05) and T_3w vs. T_10w (p_TFI<0.01; p_TQ<0.01). The percentage of patients reporting an improvement of their tinnitus at T_10w was 47%. Further analysis revealed a significant effect of gender with female patients showing a larger improvement on the TFI and TQ (p_TFI<0.01; p_TQ<0.05).

CONCLUSIONS

The current study reported the effects of HD-tDCS in a large tinnitus population. HD-tDCS of the right DLPFC resulted in a significant improvement of the tinnitus perception, with a larger improvement for the female tinnitus patients.

Effects of High-Definition Transcranial Direct-Current Stimulation on Resting-State Functional Connectivity in Patients With Disorders of Consciousness

Recently a positive treatment effect on disorders of consciousness (DOCs) with high-definition transcranial direct-current stimulation (HD-tDCS) has been reported; however, the neural modulation mechanisms of this treatment’s efficacy need further investigation. To better understand the processing of HD-tDCS interventions, a long-lasting HD-tDCS protocol was applied to 15 unresponsive wakefulness syndrome (UWS) patients and 20 minimally conscious states (MCS) patients in this study. Ten minutes of resting-state electroencephalograms (EEGs) were recorded from the patients, and the coma recovery scale-revised scores (CRS-Rs) were assessed for each patient from four time-points (T0, T1, T2, and T3). Brain networks were constructed by calculating the EEG spectral connectivity using the debiased weighted phase lag index (dwPLI) and then quantified the network information transmission efficiency by graph theory. We found that there was an increasing trend in local and global information processing of beta and gamma bands in resting-state functional brain networks during the 14 days of HD-tDCS modulation for MCS patients. Furthermore, the increased functional connectivity not only occurred in the local brain area surrounding the stimulation position but was also present across more global brain areas. Our results suggest that long-lasting HD-tDCS on the precuneus may facilitate information processing among neural populations in MCS patients.

Non-Invasive Neuromodulation for Tinnitus

Tinnitus is a prevalent disorder that has no cure currently. Within the last two decades, neuroscientific research has facilitated a better understanding of the pathophysiological mechanisms that underlie the generation and maintenance of tinnitus, and the brain and nerves have been identified as potential targets for its treatment using non-invasive brain stimulation methods. This article reviews studies on tinnitus patients using transcranial magnetic stimulation, transcranial electrical stimulation, such as transcranial direct current stimulation, alternating current stimulation, transcranial random noise stimulation as well as transcutaneous vagus nerve stimulation and bimodal combined auditory and somatosensory stimulation. Although none of these approaches has demonstrated effects that would justify its use in routine treatment, the studies have provided important insights into tinnitus pathophysiology. Moreover bimodal stimulation, which has only been developed recently, has shown promising results in pilot trials and is a candidate for further development into a valuable treatment procedure.

Impact of tDCS and HD-tDCS on tinnitus perception: A scoping review

Tinnitus is the auditory phantom perception of a sound that severely affects the quality of life of over 300,000 people in the United Kingdom alone. Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation tool, which has been investigated as a potential tinnitus management option since 2006. This study aimed to investigate the impact of tDCS and high-definition transcranial direct current stimulation (HD-tDCS) on tinnitus perception. A scoping review was undertaken using the framework by Arksey and O'malley (2005). After consideration of relevance, 38 primary research studies were included in the data charting to examine the impact of (HD-)tDCS on tinnitus. Twenty-two of the primary research studies reported significant therapeutic effects of (HD)-tDCS on tinnitus perception. However, only eight of these included a sham-control condition. The tDCS protocols in the studies were highly heterogeneous and sample sizes were generally small. More double-blind, sham-controlled trials are needed that use similar protocols and outcome measures before definitive conclusions about the efficacy of (HD-)tDCS for tinnitus can be drawn.

Effects of High-Definition Transcranial Direct Current Stimulation and Theta Burst Stimulation for Modulating the Posterior Parietal Cortex

OBJECTIVES

Noninvasive brain stimulation methods, including high-definition transcranial direct current stimulation (HD-tDCS) and theta burst stimulation (TBS) have emerged as novel tools to modulate and explore brain function. However, the relative efficacy of these newer stimulation approaches for modulating cognitive functioning remains unclear. This study investigated the cognitive effects of HD-tDCS, intermittent TBS (iTBS) and prolonged continuous TBS (ProcTBS) and explored the potential of these approaches for modulating hypothesized functions of the left posterior parietal cortex (PPC).

METHODS

Twenty-two healthy volunteers attended four experimental sessions in a cross-over experimental design. In each session, participants either received HD-tDCS, iTBS, ProcTBS or sham, and completed cognitive tasks, including a divided attention task, a working memory maintenance task and an attention task (emotional Stroop test).

RESULTS

The results showed that compared to sham, HD-tDCS, iTBS and ProcTBS caused significantly faster response times on the emotional Stroop task. The effect size (Cohen's d) was d = .32 for iTBS (p < .001), .21 for ProcTBS (p = .01) and .15 for HD-tDCS (p = .044). However, for the performance on the divided attention and working memory maintenance tasks, no significant effect of stimulation was found.

CONCLUSIONS

The results suggest that repetitive transcranial magnetic stimulation techniques, including TBS, may have greater efficacy for modulating cognition compared with HD-tDCS, and extend existing knowledge about specific functions of the left PPC.

Effects of Long-Lasting High-Definition Transcranial Direct Current Stimulation in Chronic Disorders of Consciousness: A Pilot Study

Transcranial direct current stimulation (tDCS) recently was shown to benefit rehabilitation of patients with disorders of consciousness (DOC). However, high-Definition tDCS (HD-tDCS) has not been applied in DOC. In this study, we tried to use HD-tDCS protocol (2 mA, 20 min, the precuneus, and sustaining 14 days) to rehabilitate 11 patients with DOC. Electroencephalography (EEG) and Coma Recovery Scale–Revised (CRS-R) scores were recorded at before (T0), after a single session (T1), after 7 days’ (T2), and 14 days’ HD-tDCS (T3) to assess the modulation effects. EEG coherence was measured to evaluate functional connectivity during the experiment. It showed that 9 patients’ scores increased compared with the baseline. The central-parietal coherence significantly decreased in the delta band in patients with DOC. EEG coherence might be useful for assessing the effect of HD-tDCS in patients with DOC. Long-lasting HD-tDCS over the precuneus is promising for the treatment of patients with DOC.

Adjunctive Role of Bifrontal Transcranial Direct Current Stimulation in Distressed Patients with Severe Tinnitus

BACKGROUND

This study assessed the therapeutic effect of adjunctive bifrontal transcranial direct current stimulation (tDCS) in patients with tinnitus.

METHODS

Forty-four patients who visited our university hospital with a complaint of non-pulsatile subjective tinnitus in January through December 2016 were enrolled. All patients received directive counseling and sound therapy, such as a sound generator or hearing aids, and/or oral clonazepam. Patients who agreed to undergo additional bifrontal tDCS were classified as the study group (n = 26). For tDCS, 1.5 mA of direct current was applied to the prefrontal cortex with a 10-20 EEG system for 20 minutes per session.

RESULTS

The Tinnitus Handicap Inventory (THI), Beck Depression Inventory, and Visual Analog Scale (VAS) scores decreased significantly after treatment (P < 0.001). Patients who had a moderate or catastrophic handicap were significantly more likely to respond favorably to bifrontal tDCS (P = 0.026). There was no correlation of number of tDCS sessions with change in the THI or VAS score (P > 0.05). Logistic regression analysis revealed that the initial THI score was independently associated with improvement in the THI. However, tDCS was not a significant determinant of recovery.

CONCLUSION

tDCS can be used as an adjunctive treatment in patients with severe tinnitus. Although tDCS did not decrease the loudness of tinnitus, it could alleviate the distress associated with the condition in some patients with a moderate or catastrophic handicap.

High-definition transcranial direct current simulation (HD-tDCS) for persistent auditory hallucinations in schizophrenia

Conventional transcranial Direct Current Stimulation (tDCS) has been reported to alleviate persistent auditory hallucinations (AH) in schizophrenia as an add-on intervention. High-Definition tDCS (HD-tDCS), an optimized form of tDCS, has the potential for more focalized neuromodulation. In this study, add-on HD-tDCS (5 days twice daily session with 2-mA cathodal current on left temporo-parietal junction) using 4 × 1 ring montage significantly reduced persistent AH (t = 3.6;p < 0.01) in schizophrenia patients (N = 19). Add-on HD-tDCS has promising potential to treat persisting AH in schizophrenia. This needs further systematic research.

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.