tDCS Outcomes: Sex Differences in Hearing Health

A 2026 review of 47 studies has concluded that biological sex is a significant and complex factor in how individuals respond to transcranial direct current stimulation (tDCS). The research, published in *Cells*, finds that identical tDCS protocols can produce different outcomes in women and men, a finding that has direct implications for its potential use in treating conditions like tinnitus, hyperacusis, and misophonia.

How Researchers Investigated Sex Differences in Brain Stimulation

James Chmiel, Marta Stępień-Słodkowska, and their team at the University of Szczecin conducted a structured, narrative review. They systematically searched for studies where sex—or variables the original authors labeled as gender but defined through female-male comparisons—was examined as a potential moderator of tDCS outcomes. After screening, they included 41 studies and added 6 more from citation searches, for a total of 47.

Because the studies involved vastly different participant groups, stimulation protocols, and outcome measures, a traditional meta-analysis was not possible. Instead, the researchers synthesized the evidence narratively, identifying clear patterns of when and how sex differences emerged. This approach is detailed in their paper (Cells. 2026;15(16):1474. PMID: 42645203).

Findings: Sex Effects Are Context-Dependent, Not Universal

The central finding is that sex does not produce a uniform “better” or “worse” response to tDCS. Instead, its influence is context-dependent, varying with multiple factors.

Stimulation Parameters Matter

The montage (electrode placement), cortical target, stimulation intensity, and even the placement of the reference electrode all interacted with sex. A protocol that improved performance in men on a specific task might have no effect, or even a different effect, in women. The effects were often not visible at baseline or during simple tasks but became clear during demanding cognitive challenges or in the delayed after-effects of stimulation.

Anatomy and Hormones Provide the Mechanism

Computational modeling studies indicate a primary reason for these differences: anatomy. Identical tDCS settings on the scalp result in different distributions and strengths of the intracranial electric field in women versus men, largely due to differences in skull thickness and brain volume.

Hormonal states add another layer of complexity, particularly for females. Fluctuations in hormones related to the menstrual cycle, menopause, or contraceptive use can modify cortical excitability and neurochemistry, potentially amplifying or altering the effects of tDCS. This suggests that a “one-size-fits-all” stimulation dose is physiologically improbable.

Beyond Sensation and Blinding

The team also considered whether differences in skin sensation or the ability to guess if the stimulator is active (blinding efficacy) could explain the results. While these factors may play a role at higher intensities, they do not fully account for the sex-contingent outcomes observed in behavioural and physiological data.

Practical Implications for Hearing and Sensory Disorders

This research has immediate relevance for the investigation of tDCS as a therapy for tinnitus, hyperacusis, and misophonia. These conditions involve complex brain network dysfunctions where tDCS is being explored to modulate hyperactivity or maladaptive plasticity.

The review suggests that the mixed results from past tDCS clinical trials for tinnitus could be partly due to unac (NAC supplement)counted-for sex differences. A protocol showing promise in a predominantly male study group may fail in a more balanced cohort if sex is not considered in the analysis.

For conditions like misophonia and hyperacusis, which involve strong limbic and emotional responses, hormonal influences on brain state could be particularly important. The finding that sex differences are most apparent during demanding tasks or emotional processing directly relates to the challenges faced by individuals with these conditions.

Furthermore, the link between these auditory disorders and conditions like anxiety following brain injury underscores the need for highly individualized neuromodulation approaches. A therapy that interacts with sex-based neuroanatomy and endocrinology must be carefully tailored.

A Call for Better, More Individualized Research

Chmiel and colleagues conclude with clear recommendations. They state that future tDCS research must treat sex not just as a demographic variable to be balanced, but as a “mechanistically relevant moderator” that is central to the experimental design.

This means studies should be adequately powered to detect sex-by-stimulation interactions, consider hormone-aware designs (like tracking menstrual cycle phase), and use computational modeling to estimate individual electric fields. The goal is to move from generic protocols towards individualized neuromodulation, where dose is informed by anatomy, physiology, and biological sex. This shift is essential for developing reliable, effective brain stimulation therapies for hearing and neurological health.