tDCS and Tinnitus

How effective is tDCS at treating Tinnitus: A meta analysis

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The impact of Tinnitus

Tinnitus impacts an estimated 15% of the population (). 

 

Its impact is felt in a number of different ways (as described left) and financially, as the No. 1 claimed benefit at the VA and and estimated $26 Billion in societal costs (American Tinnitus Association)

What Initiates Tinnitus?

Tinnitus usually starts with damage to the Cochlea (shown here), whether that is the nerves or hair cells. 

This damage creates abnormal or phantom signals to be created

Why does it become chronic?

The abnormal signals are processed by the primary auditory cortex (A1).  A1 has a "tonotopic map" meaning that each frequency has a specific location in the brain responsible for processing it.

A1 can fail to adapt, or incorrectly adapt to the abnormal signals., creating a chronic condition

So what can be done?

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Changing Perception

The classical approach which relies on cognitive behavioral therapy.

The idea is to improve the individual's "Cognitive Control", or their ability to control their attention.  Our brains are often really good at ignoring sounds that are unimportant, and if we train that, we can reduce the perception of the tinnitus and therefore its impact.

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Changing Sensation

New therapies, such as brain stimulation, are looking to change the sensation of tinnitus.

By changing the activity of the auditory nerves, either near the cochlea or in the primary auditory cortex, you may be able to change the volume of the tinnitus, maybe even mute it.

A meta-analytic approach

We took a meta analysis approach, which means instead of collecting new data, we take gather all of the current studies on the topic and treat those as our data points.

We searched pubmed, google scholar, and the grey literature for all studies that used tDCS as an intervention for tinnitus

Included studies with and without control groups (controlled trials vs case studies). Some studies included more than 1 treatment group, which we separated

tDCS Parameters

There are a number of different settings for tDCS that can affect the results. We tried to separate the studies based on the settings each used, hoping to figure out which settings led to the best outcomes.

Intensity

1 mA vs 1.5 mA vs 2 mA

Target Mechanism

Sensation (LTA) vs Perception (DLPFC)

Duration

10 min vs 15 min vs 20 min

Treatment Outcome

Loudness vs Annoyance

Number of Sessions

1-25 sessions of tDCS

Mechanism X Outcome

Does mechanism match outcome?

So what did we find?

Controlled Trials

Overall Effect

Overall both the controlled trials and the case studies showed a small but significant effect, such that the use of tDCS improved (reduced) tinnitus symptoms

Case Studies

Controlled Trials

Target Mechanism

Targeting the DLPFC had a much larger effect than targeting the LTA. This would suggest that tDCS is better at helping control perception, enhancing the same mechanisms as conventional therapy.  tDCS is not as effective at changing sensation, as evidenced by the smaller effect size when targeting the LTA (the auditory cortex)

Case Studies

Controlled Trials

Target Outcome

Interestingly, despite the difference in target mechanism, there was no difference in effect depending on the symptom.

This may be because of limitations in how these symptoms are calculated, but we don't know.

Case Studies

Controlled Trials

Mechanism

X

Outcome

While not surprising given the last 2 results, but there is no interaction effect between target mechanism and outcome.  Whether you are trying to reduce distress or loudness, targeting the DLPFC has a larger effect

Case Studies

So what does it all mean?

 

A small but significant effect

Our results show a benefit to using tDCS to treat tinnitus.  Surprisingly, targeting the DLPFC outperformed targeting the LTA for both perception and sensation.

Based on these results future research should focus on trying to combine tDCS to DLPFC with current Cognitive Behavioral Therapy practices.

Preprint

You can read a preprint of this meta analysis with all the details on meta-arxiv

Data

You can access all data and analysis scripts on the Open Science Framework

New Relevant Research

Since I released the preprint, a couple of large reviews, including one meta-analysis have also been published.  Both agree with the overall conclusions of my analysis.

Chen et al. 2020

Association of Central Noninvasive Brain Stimulation Interventions with Efficacy and Safety in Tinnitus Management: A Meta-analysis

JAMA Otolaryngology–Head & Neck Surger

Langguth 2020

Non-Invasive Neuromodulation for Tinnitus

Journal of Audiology and Ontology

©2020 by Alexander Cates.

ac@alexcates.com