Scientists at the Icahn School of Medicine at Mount Sinai have identified three brain pathways associated with sustained improvement in patients receiving experimental treatment for severe depression.
Published October 1, 2026, in the American Journal of Psychiatry, the findings suggest that the success of deep brain stimulation may depend on precisely which neural connections receive electrical stimulation.
The research also offers clues as to why some patients experience relief while others continue to struggle with symptoms. For a treatment still under investigation, understanding that difference could help guide future research.
The findings suggest that the precise connections brain stimulation reaches may matter as much as where the electrodes are implanted.
The researchers analyzed clinical data from several studies, including the BROADEN trial and a University of Toronto patient cohort. They examined how electrical stimulation engaged connections between brain regions and how those patterns related to treatment outcomes.
The results revealed an important distinction: patients who improved showed more consistent patterns of pathway engagement, while unsuccessful treatment was associated with insufficient stimulation of certain connections.
Three Brain Pathways Linked to Lasting Improvement
The study identified three neural connections associated with sustained improvements in depression symptoms.
The first, the cingulum bundle, connects brain regions involved in emotional and cognitive processing. The second, the forceps minor, links frontal regions across the brain’s two hemispheres.
The third involves the medial uncinate fasciculus and ventral amygdalofugal pathway, which connect frontal and emotion-related brain regions.
Scientists already knew about these pathways, but the latest findings strengthen evidence that they contribute to successful deep brain stimulation.
Rather than focusing solely on electrode placement, the research examines whether stimulation reaches the connections linked to better outcomes.
Why a Few Millimeters Could Matter
Small differences in electrode positioning may affect which neural pathways are stimulated.
Deep brain stimulation involves surgically implanted electrodes that deliver electrical signals to selected brain regions. However, electrodes placed in the same general area do not necessarily engage the same connections.
Brian Kopell, MD, Director of Mount Sinai’s Center for Neuromodulation, explained the importance of precision.
“For a network disorder such as depression, millimeters can determine whether stimulation reaches the pathways we intend to modulate,” Kopell said.
Helen Mayberg, MD, a Mount Sinai professor of neurotherapeutics, also emphasized individualized surgical targeting as a key consideration for better treatment outcomes.
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The findings support further investigation into whether understanding each patient’s brain connectivity could help researchers plan stimulation more precisely.
Related: 8 Mind-Boggling Illusions That Prove Your Brain Is Lying to You Right Now
What Patients Who Did Not Improve Revealed
Some of the study’s most revealing findings came from patients whose symptoms did not respond to treatment.
Researchers observed that patients who remained unresponsive after two years showed inadequate engagement of the left cingulum bundle. Insufficient stimulation of the medial uncinate fasciculus was also associated with reduced therapeutic effects.
These findings suggest that unsuccessful treatment may sometimes involve failing to reach connections associated with improvement.
However, the researchers did not test whether repositioning electrodes or adjusting stimulation settings could reverse unsuccessful outcomes. The distinction is important. Identifying why a treatment might fail does not automatically establish how to make it succeed.
What the Research Still Needs to Establish
The findings offer promising clues, but they do not prove that more precise targeting will guarantee relief from depression.
The October study builds on earlier investigations published in 2014, 2017, and 2023 examining brain connectivity and deep brain stimulation.
Because the latest research retrospectively analyzed existing clinical data, it cannot establish that a new targeting strategy would produce better results in a randomized trial.
Some participants also lacked individual brain scans, so researchers sometimes relied on generalized connectivity maps.
Mount Sinai reports that connectivity-guided approaches have informed the Abbott TRANSCEND randomized controlled clinical trial, which uses individualized brain connectivity maps to guide treatment.
Ki Sueng Choi, PhD, the study’s corresponding author, described precise engagement of these pathways as “a critical first step toward sustained response.”
Deep brain stimulation remains investigational for depression, and the findings do not establish permanent recovery or guaranteed improvement.
Still, the research shifts attention toward a question that could shape future treatment: not simply whether stimulation reaches the intended brain region, but whether it engages the connections that matter.
If more precise targeting could help explain why some patients improve while others do not, how might that change the future of depression treatment?
