Summary: A collaborative neuroimaging study shows that the length of a depressive episode fundamentally changes how major functional brain networks communicate. Researchers analyzed MRI scans from unmedicated patients with major depressive disorder to isolate the direct structural and functional signatures of the illness.
The findings indicate that short-term depressive episodes reduce the coupling between the brain’s executive control system and its introspective network, while chronic depression reverses this relationship: in long-term cases, worsening symptoms are associated with stronger connectivity, which may trap patients in repetitive negative thinking.
Key Facts
- Network misalignment: Depression disrupts the coordinated interaction between the Central Executive Network (CEN), responsible for focused, goal-directed behavior, and the Default Mode Network (DMN), which supports self-reflection and inward-focused thought. This disruption can produce persistent negative rumination and difficulty concentrating on external tasks.
- Chronicity threshold: According to first author Tamires Zanão, the brain shows distinct structural and functional changes when depression persists beyond about 24 months.
- Precuneus as a bridge: The precuneus functions as an integration point linking internal mental processes and outward-directed cognitive control, connecting components of both the DMN and subnetworks tied to executive function.
- Connection reversal: In non-chronic patients, connectivity between the CEN and the DMN’s precuneus weakens as symptom severity rises. In chronic patients, higher severity is linked to stronger CEN–DMN coupling.
- Gray matter alterations: Greater symptom severity correlates with volume differences in the anterior cingulate cortex and the right dorsolateral prefrontal cortex—regions long associated with mood regulation and cognitive control.
- Unmedicated cohort: The study tested 46 unmedicated patients, which helps distinguish neural signatures of depression itself from structural and functional changes produced by antidepressant treatment.
Source: FAPESP
Prevalence and study overview: Depression affects roughly 5.8% of Brazil’s population and can vary widely in symptoms, intensity, and duration. A study published in Scientific Reports examined how symptom severity (measured with the Hamilton Depression Rating Scale) and the duration of the depressive episode (chronicity) relate to brain function and structure.
Researchers from the University of São Paulo (USP) and the University of Oxford analyzed brain scans from 46 adults diagnosed with major depressive disorder. The aim was to evaluate whole-brain network interactions and grey matter volume using network modeling and voxel-based morphometry (VBM).
Overall, the results indicate that episode duration is associated with different patterns of functional connectivity between core networks, though these group-level findings are not yet precise enough to diagnose an individual case from a single scan.
“Major depression changes brain function compared with people without the disorder. Here we found that patients with chronic depression—episodes lasting more than 24 months—and those with more recent episodes display distinct patterns of connectivity between the Central Executive Network (CEN) and the Default Mode Network (DMN),” says Tamires Zanão, FAPESP fellow and first author of the paper.
The CEN includes regions such as the dorsolateral prefrontal cortex and parts of the parietal cortex and supports goal-directed attention and cognitive control. The DMN is distributed across regions including the medial prefrontal cortex, the precuneus, and the hippocampus, and is involved in self-reflection, autobiographical memory, and spontaneous thought. Because the DMN is complex, researchers often analyze its subnetworks, including those centered on the precuneus.
The precuneus does not act only within the DMN: it also links to subnetworks associated with cognitive control. This makes it a hub or “bridge” between inward-focused mental processes and external, goal-oriented cognition. Normally, the salience network helps switch attention between internal and external focus, but in depression, these switching dynamics may become dysregulated, contributing to rumination and concentration problems.
In the study, patients with more recent depressive episodes showed decreasing connectivity between the CEN and precuneus as symptoms increased. In contrast, patients with chronic depression showed the opposite pattern: higher symptom severity accompanied stronger CEN–precuneus connectivity. Other large-sample studies, including work from population databases, have reported positive correlations between CEN activity and precuneus regions in healthy individuals, suggesting the chronic pattern diverges from typical network dynamics.
The authors also found symptom-severity–related differences in gray matter volume in the anterior cingulate cortex and the right dorsolateral prefrontal cortex. The anterior cingulate is key for integrating emotion and cognition, while right-lateralized changes in the dorsolateral prefrontal cortex align with hypotheses that depression involves hemispheric imbalances in emotional processing—though the functional meaning of increased volume in this region remains to be clarified.
Because participants were unmedicated at the time of scanning, the observed structural differences are more likely to reflect features of the disorder itself rather than medication effects. The authors caution, however, that further data are needed before these findings can inform tailored clinical decisions or diagnostic tests.
Imaging data for the 46 patients were collected as part of a larger clinical trial coordinated by Professor André Brunoni (USP) and are part of ongoing research efforts. Zanão analyzed this subset during a postdoctoral fellowship at the University of Oxford with support from FAPESP.
Funding: This research was funded by FAPESP under projects 12/20911-5, 22/03266-0, and 23/13893-5.
Key Questions Answered:
A: The study points to a realignment problem between large-scale brain systems. The Central Executive Network (CEN) supports outward, goal-directed activity, while the Default Mode Network (DMN) supports inward-focused reflection. When the balance between these systems breaks down, and the salience network that normally helps switch attention is impaired, inward negative thoughts can dominate and become persistent.
A: The major insight of this work is that depression’s neural signature can change over time. During the first two years, worsening symptoms correlate with weakened connectivity between executive and introspective systems. After depression becomes chronic, network dynamics can reverse, with severe symptoms associated with stronger coupling—potentially reinforcing the depressive loop.
A: While the group-level patterns are informative, individual brains vary considerably, and current connectivity measures are not sufficiently reliable to diagnose a single person. Still, understanding time-dependent network changes offers a framework for developing more personalized therapies and future diagnostic tools.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The original journal paper was reviewed in full.
- Additional context was added by editorial staff.
About this depression and neuroscience research news
Author: Heloisa Reinert
Source: FAPESP
Contact: Heloisa Reinert – FAPESP
Image: Image credited to Neuroscience News
Original Research: Open access. “Chronicity moderates the impact of severity on central executive-default mode network functional interactions in depression” by Tamires Zanao, Piergiorgio Salvan, Lais B. Razza, Pedro Henrique Rodrigues da Silva, Andre R. Brunoni & Jacinta O’Shea. DOI: 10.1038/s41598-026-40364-2
Abstract
Chronicity moderates the impact of severity on central executive–default mode network functional interactions in depression
Neuroimaging research indicates that major depressive disorder involves dysfunctional interactions among large-scale brain networks, and that symptom variability reflects alterations in these interactions. While severity has been widely studied, the influence of episode duration (chronicity) is less explored despite its clinical importance.
This study assessed how symptom severity, chronicity, and their interaction affect functional connectivity and gray matter volume. Forty-six patients (31 female, mean age 40.5) underwent whole-brain network modeling and voxel-based morphometry. Severity was measured using the Hamilton Depression Rating Scale; chronicity was defined as episodes lasting longer than 24 months.
The primary result is that chronicity moderates how severity influences functional connectivity between the Central Executive Network (CEN) and the precuneus, a key node of the Default Mode Network (DMN). Non-chronic and chronic patients demonstrated opposite patterns: non-chronic individuals showed higher CEN–precuneus connectivity at lower severity and weaker connectivity at higher severity, while chronic patients showed the reverse. This work highlights chronicity as a critical, previously underappreciated moderator of brain–symptom relationships in depression.