Transcranial Stimulation for Tinnitus and Hearing Disorders

Why does a brain stimulation treatment work for one person with tinnitus but not another? The answer may lie in the precise “dose” of stimulation delivered. A comprehensive review published in *Brain Stimulation*, authored by 28 leading scientists including Ghazaleh Soleimani, Marom Bikson, and Sarah H. Lisanby, establishes a unified framework for understanding dose-response in transcranial brain stimulation. The work moves beyond simple settings on a machine, explaining how the physical energy interacts with biological tissue to produce a lasting change in brain function.

For patients and clinicians navigating treatments like transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS) for tinnitus, misophonia, or hyperacusis, this research explains why personalized protocols are not just beneficial but necessary.

A Three-Part Framework for Stimulation Dose

The review argues that a true “dose” of brain stimulation is not merely the intensity set on the device. Instead, it is the product of three interconnected elements: the physics of the stimulus, the physiology of the targeted brain tissue, and the mechanism of the resulting change in brain networks.

First, the **physics** refers to the specific electric field generated in the brain. Its strength, direction, and distribution are shaped by the stimulation device’s parameters and the individual’s unique head anatomy, including skull thickness and cerebrospinal fluid levels. Two people receiving the same machine setting will likely have different electric fields in their brains.

Second, the **physiology** determines how neurons respond to that electric field. Factors like the baseline excitability of the neurons, their orientation relative to the field, and the state of the brain network at that moment all influence whether the stimulation excites or inhibits activity.

Finally, the **mechanism** is the lasting change that follows. This could be the strengthening or weakening of synaptic connections (neuroplasticity), shifts in network oscillation patterns, or changes in regional blood flow. The desired clinical outcome, such as a reduction in tinnitus loudness or hyperacusis distress, depends on this final step.

Why “One-Size-Fits-All” Stimulation Often Fails

A central finding of this work is that individual variability breaks the simple link between device settings and brain response. “The same nominal dose administered to two different individuals… can lead to markedly different electric fields in the brain,” the authors note. This variability explains the mixed results often seen in clinical trials for hearing disorders.

For example, a standard TMS protocol for tinnitus might target the left auditory cortex. However, if a person’s auditory cortex sits deeper in a sulcus (a fold in the brain), the electric field from a standard coil may be too weak to modulate it effectively. Similarly, a brain in a hyper-aroused state due to the stress of chronic hyperacusis may respond differently to tDCS than a calmer brain. This physiological context is part of the dose.

This complexity is echoed in research on auditory pathway evaluation, which shows that tinnitus involves diverse neural signatures. A stimulation protocol must account for this diversity to be effective.

Practical Implications for Hearing Disorder Treatments

This framework has direct consequences for developing and applying neuromodulation therapies.

**Treatment Personalization:** The future of stimulation for conditions like tinnitus and misophonia lies in dosing that accounts for individual anatomy and brain state. Techniques like computational electric field modeling, using a person’s own MRI scan to predict field strength, are a direct application of this physics-first principle. This approach aligns with a more personalized model of tinnitus care that integrates sensory and emotional processing.

**Trial Design and Outcome Measurement:** Clinical studies need to move beyond reporting just device settings. Researchers should measure or estimate the actual electric field in the brain (the “physics” dose) and account for brain state (the “physiology” dose). This will help clarify why some participants respond and others do not, leading to more robust and replicable protocols. This precision is as important in brain stimulation as it is in predicting recovery from sudden hearing loss.

**Mechanism-Driven Protocols:** Understanding the intended mechanism—for instance, suppressing hyperactivity in a specific auditory network versus strengthening connections to the frontal cortex for better sound tolerance—should guide the choice of stimulation site and pattern. This shift from symptom-based to mechanism-based dosing could improve outcomes for refractory cases.

A Roadmap for More Effective Neuromodulation

The 2026 review by Soleimani and colleagues provides a critical roadmap. It shifts the question from “What setting should we use?” to “What electric field do we need to create in this specific brain, in this specific state, to trigger a specific therapeutic change?”

For patients, this means that effective neuromodulation is increasingly seen as a tailored medical intervention, not a generic device application. It explains why finding an effective treatment may require careful titration and targeting, much like finding the right medication and dosage. This biological individuality extends beyond hearing, influencing broader health trajectories as seen in research on biological aging markers.

The full details of this unified framework are available in the open-access article “Dose-response relationships in transcranial brain stimulation: Physics, physiology and mechanism” (PMID: 41802460, DOI: 10.1016/j.brs.2026.103067). This work consolidates decades of research into a clear guide for developing the next generation of precise, reliable brain stimulation therapies for hearing and brain health.

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