Deep Brain Stimulation for Depression: Why Does It Work for Some but Not Others?
For people with treatment-resistant depression, standard medications and psychotherapy often fail to provide adequate relief. Deep brain stimulation (DBS) is an experimental neuromodulation therapy in which electrodes are surgically implanted in the brain to deliver controlled electrical signals to depression-related circuits. However, even small differences in electrode placement can lead to very different outcomes.
Now, researchers at the Icahn School of Medicine at Mount Sinai have published a study in the American Journal of Psychiatry analyzing the largest multi-center cohort of patients with treatment-resistant depression to date, revealing three key white matter pathways closely associated with lasting benefit from DBS.
Three Key Brain Connections Identified
By combining computer models of the electrical fields generated by implanted electrodes with brain connectivity maps, the team estimated which pathways were actually stimulated. They found that sustained improvement was consistently associated with engagement of three white matter pathways:
- The cingulum bundle: a major fiber tract connecting multiple brain regions involved in mood regulation.
- The forceps minor: a fiber pathway connecting the left and right prefrontal cortex.
- The medial uncinate fasciculus/ventral amygdalofugal pathways: pathways involved in emotional information transfer between the amygdala and prefrontal cortex.
Notably, across study sites, patients who had not responded after two years showed a lack of stimulation engagement with the left cingulum bundle. This offers a possible explanation for why apparently similar electrode placements can produce different clinical outcomes.
From Anatomical Landmarks to Connectome-Based Targeting
Traditionally, electrode placement has been guided primarily by anatomical landmarks. But electrical stimulation does not simply affect tissue closest to the electrode—it can influence larger networks through white matter pathways. As a result, two patients with nearly identical electrode locations may experience very different outcomes depending on which connections are actually engaged.
"For a network disorder such as depression, millimeters can determine whether stimulation reaches the pathways we intend to modulate," said Brian Kopell, MD, Director of the Center for Neuromodulation at Mount Sinai. "Identifying and reproducibly engaging those pathways gives us a more precise surgical target and a framework for understanding why otherwise similar electrode placements may produce different clinical outcomes."
This strategy, known as connectome-based targeting, has already helped shape the ongoing Abbott TRANSCEND randomized controlled trial, which uses individualized brain connectivity maps to guide electrode placement.
Toward More Personalized Depression Treatment
The researchers emphasize that electrode placement alone is unlikely to determine whether a patient improves. While the study focused on identifying which connections should be stimulated, further research is needed to determine which individuals are most likely to benefit and how stimulation settings—such as amplitude, frequency, and pulse width—should be adjusted over time.
The study also had limitations: individual diffusion MRI scans were not available for every participant, so much of the analysis used generalized brain connectivity maps rather than patient-specific maps. However, in the Emory patient group, results from generalized maps and individual imaging were consistent, supporting the importance of the identified pathways.
"Our findings show precisely engaging these white matter pathways is a critical first step toward sustained response," said Ki Sueng Choi, PhD, Associate Professor and Imaging Core Leader at the Center for Advanced Circuit Therapeutics at Mount Sinai, and corresponding author of the study. "The next step is to characterize abnormal functional and structural brain states along these pathways to build more detailed models for setting patient-specific stimulation parameters."
What This Means for Patients
- DBS remains an experimental therapy for severe, persistent depression that has not responded to conventional treatments, and should be evaluated by specialized teams.
- Precision of electrode placement directly affects outcomes; centers with brain connectivity mapping capabilities may offer advantages.
- Depression is a complex network disorder requiring multidisciplinary care and long-term follow-up.
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