Sex Differences in tDCS for Hearing Disorders

A 2026 narrative review analyzing 47 studies concludes that sex is a key, biologically based factor influencing the effectiveness of transcranial direct current stimulation (tDCS). The work by researchers from the University of Szczecin and Pomeranian Medical University, published in *Cells*, demonstrates that identical tDCS settings do not produce identical results in women and men.

How Researchers Investigated Sex Differences in tDCS

James Chmiel, Marta Stępień-Słodkowska, and colleagues conducted a structured review of the literature. They identified studies where sex—or variables reported as gender but operationalized as female-male group comparisons—was examined as a moderator of tDCS outcomes. After screening, they included 41 studies, with 6 more found through citation searching, for a total of 47 studies analyzed.

Because the studies involved diverse populations, tDCS protocols, and outcome measures, a traditional meta-analysis was not feasible. Instead, the team synthesized the findings narratively, looking for consistent patterns across behavioural, physiological, clinical, and computational modelling research. This approach allowed them to build a comprehensive picture of how and when sex differences matter.

Findings: Why Sex Matters in Brain Stimulation

The review found that sex-related effects are common but not uniform. They depend heavily on specific factors of the tDCS protocol and the task being performed.

Anatomy and Computational Models

Computational modelling studies provided a clear, physical explanation for some of the variability. Identical electrode placement and stimulation intensity can generate different intracranial electric fields in women and men. This is due to anatomical differences, such as skull thickness and brain volume, which alter how the electrical current travels and distributes within the brain.

The Role of Hormones and Task Context

Hormonal and endocrine states, particularly fluctuating hormone levels in females across the menstrual cycle, can modify or amplify tDCS effects. Furthermore, sex differences were most apparent during cognitively demanding tasks, in later phases of learning, or when measuring delayed after-effects of stimulation. This suggests that baseline brain state and neural reserve interact with sex to shape outcomes.

The effects frequently emerged as interaction effects. For example, a specific montage might benefit men but not women, or show opposite effects depending on sex. The authors note that while factors like sensation and tolerability under higher-intensity protocols may differ by sex, these factors alone do not explain the observed, context-dependent outcomes in performance and physiology.

Practical Implications for Hearing and Sound Sensitivity Disorders

This research has direct relevance for the investigation of tDCS as a treatment for conditions like tinnitus, hyperacusis, and misophonia. Many research protocols and early clinical applications have used a one-size-fits-all approach to stimulation parameters.

The findings argue strongly against this. For instance, a tDCS protocol showing promise for tinnitus or hyperacusis in a mixed-sex study might be effective only for a subset of participants, with sex being a key determining factor. This could explain some of the inconsistent results seen in neuromodulation trials for these conditions. Individual differences in auditory processing, which may be influenced by sex, could interact with tDCS in complex ways.

The review also connects to broader themes in personalized medicine for hearing health. Just as understanding individual hearing profiles is essential, so too is understanding individual neuroanatomical and neuroendocrine profiles when applying brain stimulation.

A Call for Better Study Design and Individualized Treatment

Chmiel and co-authors conclude that sex influences tDCS outcomes through a combination of anatomical, hormonal, and task-related mechanisms. To improve the reproducibility of tDCS research and its clinical translation, they issue clear recommendations.

Future studies must treat sex as a mechanistically relevant biological variable, not just a demographic checkbox. This requires dose-aware designs that consider how anatomy affects current flow, and hormone-aware designs that track menstrual cycle phases in female participants. Studies must also be adequately powered to detect sex-by-treatment interactions, which are often missed in underpowered trials.

For patients and clinicians, this research points toward a future of more individualized neuromodulation. Effective tDCS therapy for auditory disorders may eventually require protocols tailored not just to the condition, but to the individual’s sex, anatomy, and even current physiological state. This precision mirrors a growing trend in behavioural therapies, where factors like baseline mood are recognized as key modifiers of outcome, as seen in research on CBT-I outcomes.

The paper, “Sex Does Matter! The Influence of Sex on Outcomes of Transcranial Direct Current Stimulation (tDCS)” (doi: 10.3390/cells15161474), establishes that accounting for sex is not an optional extra in neuromodulation science—it is a fundamental requirement for building effective, reliable treatments.