Schizophrenia affects roughly one in every hundred people worldwide, and while antipsychotic medications control many of its features, a substantial fraction of patients continue to experience persistent auditory hallucinations, hearing voices that no one else can hear, as well as entrenched negative symptoms such as social withdrawal, emotional flatness, and loss of drive. These residual symptoms are among the most disabling aspects of the illness and are notoriously resistant to pharmacological escalation. This therapeutic gap has fueled decades of interest in brain stimulation techniques that might modulate the dysfunctional neural circuits thought to underlie them, offering hope for patients who have exhausted conventional options.

The technique tested in STIM’Zo belongs to a family of methods known as low-intensity transcranial electrical stimulation. Unlike transcranial magnetic stimulation, which uses rapidly changing magnetic fields to induce currents strong enough to trigger neuronal firing, transcranial electrical stimulation delivers currents so weak, typically on the order of one to two milliamps, that they do not directly cause neurons to discharge. Instead, these faint currents subtly shift the resting electrical potential of cortical neurons, nudging their excitability up or down depending on the stimulation protocol. Transcranial direct current stimulation applies a steady current, whereas tRNS delivers current that fluctuates randomly across a range of frequencies, a design intended to prevent the brain from habituating to a constant signal and to exploit the tendency of neural networks to resonate with stochastic input.

Earlier evidence for tRNS and its close cousin tDCS in schizophrenia rested on a fragile foundation of case reports and small pilot studies, some of which reported striking reductions in hallucination severity. Encouraged by these signals, the STIM’Zo investigators, led by Jerome Brunelin, Marine Mondino, and Emmanuel Poulet and their collaborators, designed a definitive test. The trial was registered as NCT02744989 and received support from the French Ministry of Health, the NeuroDis foundation, and the Centre Scientifique de Monaco, with no funder involvement in the design, analysis, or reporting of the study.

The trial’s methodology reflects the highest standard of clinical rigor. Triple-blind means that patients, the clinicians assessing outcomes, and the statisticians analyzing the data all remained unaware of who received active stimulation and who received sham. The sham condition was engineered to mimic the sensations of real stimulation, typically a brief tingling or itching at the electrode sites at the start of each session, without delivering therapeutic current. Patients were randomized across multiple centers, and the primary outcome was defined in advance as clinical response at Day 5, operationalized as a reduction of at least 25 percent on the total score of the Positive and Negative Syndrome Scale, the most widely used standardized instrument for measuring schizophrenia symptom severity. Secondary outcomes tracked symptoms at one, three, and six months using additional instruments including the Auditory Hallucinations Rating Scale, the Calgary Depression Scale for Schizophrenia, the Clinical Global Impression scale, and a schizophrenia-specific quality of life questionnaire.

The primary analysis included 132 patients, 64 in the active stimulation group and 68 in the sham group, with balanced sex distributions across arms. The result was unambiguous. At Day 5, only 6 of 64 patients in the active group, or 9.4 percent, met the response criterion, compared with 9 of 68 patients, or 13.2 percent, in the sham group. The difference between groups was not statistically significant, with an effect estimate of negative 0.38 and a 95 percent confidence interval spanning negative 1.64 to 0.89, and a p value of 0.56. In plain terms, the sham procedure performed slightly, though not significantly, better than the real intervention. None of the secondary outcomes, measured over the following six months, showed significant differences either, meaning the stimulation neither reduced hallucinations, nor improved negative symptoms, nor lifted mood or quality of life beyond what the placebo ritual itself achieved.

Safety, at least, was not in question. Serious adverse events unrelated to treatment occurred in five patients in the active group and seven in the sham group, a difference that was not statistically significant. The technique was well tolerated, and the trial confirmed that low-intensity electrical stimulation of this kind carries no meaningful physical risk when properly administered. But safety without efficacy is a hollow consolation for patients and clinicians, and the authors’ conclusion was blunt: tRNS did not show superiority over sham in reducing persistent symptoms of schizophrenia.

Why did a technique that showed promise in early studies fail so decisively here? The most instructive answer lies in the trial design itself. Small pilot studies and case reports are exquisitely vulnerable to placebo effects, publication bias, and regression to the mean, and psychiatric symptoms are especially susceptible to the powerful psychological ritual of receiving what feels like an active treatment. The sham group’s 13.2 percent response rate illustrates how much apparent improvement can arise from expectation, attention, and the natural fluctuation of symptoms alone. When these factors are rigorously controlled, as they were in STIM’Zo, the true effect of the intervention can shrink dramatically or vanish. The trial also raises deeper questions about mechanism: whether currents this weak, applied over the scalp and attenuated by skull and skin, can reach and meaningfully alter the deep and distributed circuits implicated in hallucinations remains uncertain. Some researchers argue that stimulation parameters, electrode positioning over regions such as the temporoparietal junction and dorsolateral prefrontal cortex, or the duration of treatment may need optimization, but the STIM’Zo data provide no support for the technique in its current form.

The implications extend well beyond tRNS. The result tempers enthusiasm for a wave of consumer and clinical enthusiasm around electrical brain stimulation for psychiatric conditions, and it underscores the necessity of large, triple-blind, sham-controlled trials before any brain stimulation protocol is adopted into routine care. It also offers a model of how the field should proceed: preregistered endpoints, multicenter recruitment, transparent funding, and honest reporting of negative results. For the patients who participated, and for the millions living with persistent voices and blunted lives, the trial did not deliver a new therapy, but it delivered something arguably just as valuable, a clear and trustworthy answer that redirects research toward approaches with a genuine chance of working. In science, knowing what does not work, and knowing it with confidence, is the first step toward finding what does.

Subject of Research: A triple-blind randomized trial testing transcranial random noise stimulation as an add-on treatment for persistent symptoms in schizophrenia.

Article Title: Low intensity transcranial electrical stimulation for schizophrenia: a triple-blind, randomized, sham-controlled multicenter trial (STIM’Zo)

Article References: Brunelin, J., Mondino, M., Plaze, M., Attal, J., Benoit, M., El-Hage, W., Galvao, F., Haesebaert, J., Jardri, R., Llorca, P. M., Magaud, L., Nathou, C., Szekely, D., Fakra, E., & Poulet, E. (2026). Low intensity transcranial electrical stimulation for schizophrenia: a triple-blind, randomized, sham-controlled multicenter trial (STIM’Zo). BMC Medicine. https://doi.org/10.1186/s12916-026-05227-7

Image Credits: AI Generated

DOI: 10.1186/s12916-026-05227-7

Keywords: schizophrenia, tRNS, brain stimulation, auditory hallucinations, negative symptoms, placebo-controlled trial, BMC Medicine, psychiatry, tDCS, clinical trial, PANSS, noninvasive stimulation

At the heart of this investigation lies the dorsolateral prefrontal cortex (dlPFC), a critical brain region extensively involved in executive functions such as working memory, attentional control, and problem-solving. The researchers hypothesized that electrically stimulating this area might optimize its functional connectivity and facilitate cognitive processes essential for mathematical reasoning. This neural enhancement is believed to fine-tune the dlPFC’s ability to coordinate with other brain regions, particularly the posterior parietal cortex, which plays a pivotal role in numerical cognition and spatial processing.

The study’s methodology was meticulous and rigorous. Seventy-two healthy adults aged between 18 and 30 participated in a carefully structured five-day mathematics training program. The cohort was divided equally into three groups: one receiving tRNS targeting the dlPFC, another receiving stimulation over the posterior parietal cortex, and a control group subjected to sham stimulation. This design allowed the researchers to dissect region-specific effects of the intervention and contrast them against placebo conditions, thereby isolating the efficacy of dlPFC stimulation.

Neuroimaging data yielded compelling evidence that individuals exhibiting stronger intrinsic brain connectivity between the dlPFC and posterior parietal cortex naturally performed better in mathematical learning tasks. Intriguingly, for those with weaker connectivity—traditionally linked to poorer math skills—applying tRNS to the dlPFC produced significant enhancements in learning outcomes. This suggests a capacity for neurostimulation to compensate for underlying biological limitations, thereby leveling the cognitive playing field.

The biochemical dimension of the study, focusing on gamma-aminobutyric acid (GABA) levels, further enriched these insights. GABA, the primary inhibitory neurotransmitter in the human brain, is intricately involved in synaptic plasticity and learning processes. Participants who showed greater improvements in mathematical performance following neurostimulation tended to have lower baseline GABA concentrations. This observation aligns with prior findings from the same team that underscored the role of GABAergic signaling in modulating learning trajectories from childhood through adulthood.

This fusion of neurophysiological and neurochemical data underscores a nuanced, multilayered understanding of how targeted brain stimulation can optimize cognitive function. The ability to modulate not only the structural connectivity but also the neurochemical milieu is a pioneering stride in cognitive neuroscience. It opens avenues for tailored, biologically informed educational strategies that transcend traditional environmental interventions focused solely on teaching methods or curriculum design.

Professor Roi Cohen Kadosh, the study’s lead author and Head of the School of Psychology at the University of Surrey, emphasized this paradigm shift in educational neuroscience. He pointed out that most prior efforts aimed at improving education have concentrated on altering external factors, such as teaching quality or learning environments. Nevertheless, a growing body of evidence reveals that intrinsic neurobiological factors often exert a stronger influence on mathematical proficiency than previously appreciated. By integrating neuroscience with education, we can devise innovative interventions that directly address learner-specific biological constraints.

One of the most striking implications of this research pertains to the so-called ‘Matthew effect’ in education, whereby early advantages in learning accumulate into long-term disparities. This effect often results in a widening gap between high achievers and those who struggle, reinforcing systemic inequalities over time. The findings from this study point toward neurostimulation as a viable tool to mitigate this effect by enhancing brain function in individuals with suboptimal connectivity, thereby fostering more equitable learning outcomes.

As nations worldwide grapple with the challenge of boosting numeracy skills among young adults, this research arrives at a crucial moment. In the UK, for example, policymakers are actively seeking evidence-based approaches to improve mathematical competencies across the 16-to-19 age group. This study’s identification of a biological basis for learning differences, coupled with a scalable intervention method, could inform future educational policies and funding allocations, ultimately shaping more effective and inclusive teaching paradigms.

Importantly, the safety profile of transcranial random noise stimulation makes it an attractive candidate for broader application. The technique is painless, non-invasive, and transient, minimizing the risks typically associated with more aggressive neurostimulation methods. As the field advances, larger-scale trials beyond controlled laboratory settings are needed to validate and refine these initial promising findings, as well as to explore the long-term cognitive and behavioral impacts.

Moreover, the interplay between brain connectivity and neurotransmitter systems highlighted by this study paves the way for personalized education trajectories. By assessing an individual’s unique neurobiological profile, educators and clinicians could customize interventions—whether neurostimulation, pharmacological support, or cognitive training—to optimize learning efficacy. This bespoke approach heralds a future where neuroeducation becomes as much about the brain’s biology as about pedagogical technique.

Overall, the University of Surrey-led research ushers in a new era of interdisciplinary science converging psychology, neuroscience, and education. It demonstrates that brain stimulation techniques like tRNS hold immense potential not only as research tools but also as practical instruments to enhance human cognitive capabilities. As we deepen our grasp of how functional connectivity and neurochemical signaling regulate learning, the prospect of making education more accessible, effective, and equitable becomes increasingly tangible.

This study, published in the prestigious journal PLOS Biology, exemplifies how fundamental research can lead to transformative societal impacts. Through continued exploration of the brain’s intricate networks and their modulation, we are moving closer to unlocking the untapped potential of millions who face challenges in mathematics and beyond.

Subject of Research: Non-invasive brain stimulation and its effect on mathematical learning through modulation of dorsolateral prefrontal cortex connectivity and GABAergic signaling.

Article Title: Functional connectivity and GABAergic signaling modulate the enhancement effect of neurostimulation on mathematical learning

News Publication Date: 1-Jul-2025

Web References: https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3003200

References: The study published in PLOS Biology, funded by European Research Council and Wellcome Trust.

Image Credits: University of Surrey

Keywords: Mathematics, Central nervous system, Prefrontal cortex