Transcranial magnetic stimulation, a non-invasive neuromodulation technique, uses magnetic pulses to influence neural activity in specific brain regions. Since receiving FDA approval in 2008 for major depressive disorder, TMS has grown in clinical utility, particularly for patients unresponsive to traditional pharmacological and psychotherapeutic interventions. Historically, determining the target site for TMS has relied on surface anatomical landmarks on the scalp, which serve as proxies for underlying brain structures. While pragmatically sound and easily accessible for widespread clinical use, this traditional approach lacks customization to the patient’s unique brain circuitry, potentially limiting therapeutic gains.

The innovation introduced by this study lies in leveraging functional magnetic resonance imaging (fMRI) to identify individualized treatment targets based on resting-state functional connectivity. This imaging modality measures synchronized activity patterns amongst disparate brain regions while subjects are at rest. By parsing these connectivity networks, the research team pinpointed precise loci within the brain circuits implicated in depression, thereby refining the spatial accuracy of stimulation. This neuroimaging foundation enables a more tailored intervention that accounts for the heterogeneity of depression at the circuit level.

Of particular note is the application of accelerated TMS (aTMS), which compresses multiple treatment sessions into a single day, thereby shortening the overall treatment course from several weeks to a mere week. This intensification not only improves patient convenience but may enhance neurobiological receptivity to stimulation by delivering more frequent pulses within a condensed timetable. The study set out to compare the clinical outcomes of aTMS when targets were defined by fMRI connectivity versus the established scalp-based targeting.

The trial enrolled 40 adult participants with moderate to severe treatment-resistant major depression, spanning a broad age range of 22 to 80 years. Each individual underwent pre-treatment fMRI scanning to delineate functional connectivity profiles. Subsequently, subjects were randomized to receive aTMS directed either at their individualized connectivity-based target or the conventional scalp-based target. Crucially, both patients and clinical raters were blinded to group assignments to mitigate bias.

One month post-treatment assessments revealed that the group receiving connectivity-guided aTMS demonstrated significantly greater alleviation of depressive symptoms compared to their scalp-based counterparts. These improvements were quantified using the Montgomery-Åsberg Depression Rating Scale (MADRS), a gold-standard clinician-administered instrument that sensitively captures changes in depression severity. Furthermore, the response rate — defined by clinically meaningful symptom reduction — was markedly higher in the connectivity group, with 80% responding versus 60% in the traditional targeting group, underscoring the potential clinical advantage of imaging-informed intervention.

This research builds upon prior explorations led by Joseph Taylor and colleagues, including investigations into imaging-based modulation of anxiety circuits within depressive populations, as recently reported in Molecular Psychiatry. These cumulative findings lend prospective support to the concept that precision neuroimaging can transcend theoretical neuroscience and play a direct role in augmenting therapeutic outcomes.

Taylor emphasizes the significance of closing the gap between neuroimaging research and tangible clinical benefit. Historically, the complexity and additional cost associated with imaging have created barriers to its routine clinical adoption for TMS guidance. This study represents a crucial step toward justifying such investment by empirically demonstrating a quantifiable benefit above conventional practice, a vital incentive for healthcare providers and payers considering integration of this technology.

Despite the promising results, the authors acknowledge particular study limitations, including the modest sample size and single-center study design, which may affect generalizability. They advocate for larger, multi-site trials to validate these early findings and explore durability of treatment effects over extended follow-up periods. Broadening the participant demographics will also be essential to ascertain the utility of connectivity-based targeting across diverse patient populations and varying clinical subtypes of depression.

This trial’s implications extend beyond depression, suggesting that functional brain imaging could inform individualized treatment strategies for a range of psychiatric disorders treatable by neuromodulation, including anxiety, obsessive-compulsive disorder, and post-traumatic stress disorder. As aTMS and neuroimaging technologies continue to evolve and become more accessible, the integration of connectivity-guided targeting holds promise for ushering in a new era of personalized psychiatry grounded in neurobiological precision.

In conclusion, the Mass General Brigham team’s randomized controlled trial provides compelling evidence that connectivity-based targeting via functional MRI can substantially enhance the antidepressant impact of accelerated TMS treatment in individuals with refractory depression. This approach offers a paradigm shift toward precision-guided neuromodulation, with the potential to improve patient outcomes and redefine clinical standards for brain stimulation therapies in psychiatric care.

Subject of Research: People

Article Title: Connectivity- versus scalp-based targeting of accelerated TMS for depression: A randomized trial

Web References:

• https://jamanetwork.com/journals/jamapsychiatry/fullarticle/10.1001/jamapsychiatry.2026.1100
• https://www.massgeneralbrigham.org/en/about/neuroscience-institute
• https://www.massgeneralbrigham.org/en/about/complex-psychiatric-care

References:
Taylor, J. et al. “Connectivity- versus scalp-based targeting of accelerated TMS for depression: A randomized trial,” JAMA Psychiatry, DOI: 10.1001/jamapsychiatry.2026.1100

Keywords:
Depression, Transcranial magnetic stimulation, Accelerated TMS, Functional magnetic resonance imaging, Functional connectivity, Neuroimaging-guided neuromodulation, Treatment-resistant depression, Personalized psychiatry, Montgomery-Åsberg Depression Rating Scale

Bipolar disorder, characterized by cyclical mood fluctuations ranging from manic highs to depressive lows, has long challenged clinicians and neuroscientists alike due to its complex pathophysiology. At the core of the disorder lies dysfunction within the frontolimbic network, an interconnected circuit bridging prefrontal cortical regions with limbic structures such as the amygdala and hippocampus. These areas collectively orchestrate emotional regulation, cognitive control, and stress responsiveness. Aberrant signaling and connectivity within this network have been implicated in mood dysregulation, yet the neurobiological mechanisms through which lithium exerts its mood-stabilizing effects have remained elusive.

Leveraging advanced neuroimaging modalities including functional magnetic resonance imaging (fMRI), structural MRI, and positron emission tomography (PET), the authors meticulously reviewed data spanning multiple longitudinal and cross-sectional studies. Their synthesis emphasizes lithium’s multifaceted impact on brain structure and function, revealing distinct neuroplastic changes that correlate with symptomatic improvement in bipolar patients. Notably, lithium administration was associated with volumetric increases in the anterior cingulate cortex and hippocampus — regions integral to emotional processing and memory consolidation.

Functional connectivity analyses demonstrated that lithium modulates communication pathways within the frontolimbic circuitry, effectively restoring balanced activation patterns between prefrontal cortical areas involved in top-down regulation and limbic regions generating emotional salience. This rebalancing is hypothesized to underlie lithium’s therapeutic efficacy by diminishing hyperactivity in the amygdala during manic episodes and enhancing prefrontal inhibitory control during depressive phases. These findings extend previous models which portrayed lithium primarily as a neuroprotective agent, highlighting a dynamic neuromodulatory role in affective circuit function.

The reviewed literature also sheds light on lithium’s influence at the molecular and cellular levels, as neuroimaging evidence aligns with preclinical data showing lithium-induced upregulation of neurotrophic factors such as brain-derived neurotrophic factor (BDNF). This cascade promotes synaptogenesis and dendritic arborization, fostering brain resilience to stress and maladaptive neural plasticity. Importantly, the degree of frontolimbic structural alterations corresponded with clinical outcomes, implying that imaging biomarkers could be leveraged to predict individual responses to lithium therapy.

Furthermore, the neuroimaging studies uncovered regional specificity in lithium’s actions. While hippocampal and anterior cingulate cortex volumes were consistently increased, subcortical structures including the amygdala exhibited more nuanced changes dependent on treatment duration and patient heterogeneity. This spatially selective neuroplasticity underscores the complex pharmacodynamics of lithium, demanding a personalized approach to treatment planning and monitoring.

This systematic review also critically addresses methodological challenges in neuroimaging research on bipolar disorder. The authors highlight variability in imaging protocols, sample sizes, and clinical characterization as limiting factors in data synthesis. They advocate for standardized imaging acquisition and analysis pipelines alongside incorporation of multimodal imaging techniques to capture lithium’s multidimensional effects more comprehensively. Longitudinal studies with integrated clinical and cognitive assessments are emphasized as essential to unravel causative relationships between neural changes and mood symptomatology.

From a clinical perspective, these insights reinforce lithium’s irreplaceable role despite the advent of novel mood stabilizers and antipsychotic agents. Rather than being a blunt instrument, lithium emerges as a sophisticated modulator of dysfunctional neural circuits responsible for mood dysregulation. This knowledge empowers clinicians with a biologically grounded rationale for lithium use, potentially enhancing patient adherence and informing dosage optimization.

The review also opens exciting possibilities for future research. Identifying specific frontolimbic biomarkers associated with lithium responsiveness could revolutionize treatment stratification in bipolar disorder, mitigating trial-and-error prescribing that prolongs patient suffering. Moreover, combining neuroimaging with emerging genetic and pharmacogenomic data may elucidate the complex interplay between individual biological signatures and lithium’s pharmacodynamic profile.

Beyond bipolar disorder, understanding lithium’s modulation of frontolimbic circuitry has broader implications. Given this network’s involvement in major depressive disorder, anxiety disorders, and neurodegenerative diseases, lithium’s neuroplastic and neuroprotective properties could be harnessed for a spectrum of neuropsychiatric conditions. This could pave the way for novel therapeutic strategies that transcend traditional diagnostic boundaries.

In essence, Boere and colleagues have synthesized a rich body of neuroimaging evidence to articulate a refined model of lithium’s action in the brain. Far from a one-dimensional mood stabilizer, lithium appears to recalibrate dysfunctional frontolimbic circuits through neuroplastic enhancements, restoring equilibrium in emotional and cognitive processing hubs. This transformative perspective not only advances scientific understanding but also has the potential to reshape clinical approaches to bipolar disorder and related illnesses.

As this field continues to evolve, integrating neuroimaging biomarkers into routine psychiatric practice may become a reality. The prospects of precision medicine tailored to neural circuit dynamics hold promise for improving outcomes and quality of life for millions affected by mood disorders worldwide. Lithium thus remains a shining example of how decades-old treatments can gain new relevance when illuminated by cutting-edge neuroscience.

With ongoing research, the mysteries of lithium’s molecular targets and their circuit-level manifestations will unravel further, catalyzing innovative interventions. This review stands as a landmark contribution, charting a path toward a future where the neurobiology of mood stabilization is understood in unprecedented detail — a future bringing hope to the millions who battle the relentless tides of bipolar disorder.

Subject of Research: Lithium effects on frontolimbic brain circuitry in bipolar disorder studied via neuroimaging.

Article Title: Lithium effects in the frontolimbic circuitry: a systematic review of neuroimaging findings in bipolar disorder.

Article References:
Boere, E., van der Wee, N.J.A. & de Leeuw, M. Lithium effects in the frontolimbic circuitry: a systematic review of neuroimaging findings in bipolar disorder. Transl Psychiatry (2026). https://doi.org/10.1038/s41398-026-03868-z

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41398-026-03868-z