Researchers at the University of Helsinki measured brain activity in 263 people with major depressive disorder and 75 healthy control subjects, identifying five distinct neurofunctional profiles under a single diagnosis.
Depression affects roughly 332 million adults globally, according to 2025 figures from the World Health Organization. Yet two individuals with vastly different symptoms often receive the exact same clinical label. A team in Finland investigated whether this clinical individuality manifests directly in brain function.
The study, published in Nature Mental Health, was carried out in collaboration with Aalto University and the Helsinki and Uusimaa Hospital District. By analyzing how different brain regions communicate simultaneously, the research team found that major depressive disorder is far from a biologically uniform condition.
Five Distinct Profiles of Functional Connectivity
To capture these differences, investigators divided the patient cohort into five distinct groups based on the strength and frequency of connectivity between brain regions. These patterns revealed sharp contrasts in underlying neurobiology.
- Group 1: Displayed fairly strong connectivity between brain regions, accompanied by broadly severe symptoms where depression, anxiety, rumination, and reduced functional capacity were pronounced.
- Group 2: Characterized by weak connectivity between brain regions, with overall symptoms appearing milder compared to the other groups.
- Group 3: Marked by weak connectivity across a large part of the brain, with post-traumatic stress disorder emphasized heavily among symptoms.
- Group 4: Showed varying connectivity, featuring a mix of weak and strong connections alongside pronounced depression severity, substance abuse, and poor wellbeing.
- Group 5: Exhibited the strongest inter-region connectivity among all groups, with pronounced substance abuse and fewer traumatic symptoms than others.
All five profiles differed significantly from healthy control subjects. The divergence appeared not only in the intensity of connectivity but also in the specific brain regions affected and the frequency at which the connectivity occurred. In some individuals, functional connectivity was stronger than usual, while in others it was notably weaker.
Recording Brain Activity with Millisecond Precision
To map these subtle variations, the research team used magnetoencephalography (MEG) to measure brain activity in the study participants. MEG detects weak magnetic fields generated by electrical activity inside the brain.
MEG enabled us to monitor electrical brain activity with millisecond precision, helping us get closer to what actually happens in the brain at any given moment.
Satu Palva, Director of the Neuroscience Center, University of Helsinki
This high-resolution approach addresses a historical hurdle in psychiatric research. Previously, depression phenotypes have been studied using methods with slower responses.
Implications for Future Treatments and Immune Factors
Current depression diagnoses rely exclusively on behavioral symptomatology. Consequently, available FDA-approved treatments—many discovered serendipitously—leave roughly 30 to 50 percent of patients unresponsive. This therapeutic gap is thought to stem from a lack of specificity in targeting underlying pathophysiological mechanisms.
Beyond neural connectivity, researchers examining the broader biological landscape note that subsets of patients with major depressive disorder exhibit higher levels of multiple inflammatory markers, including interleukin 6 and circulating leukocytes. Children with higher circulating levels of interleukin 6 at age 9 face a 10 percent greater risk of developing major depressive disorder by age 18 compared to the general population, according to recent human research cited in neuroimmune literature.
While biological criteria are not yet used to diagnose depression directly, emerging anti-inflammatory trials show promise. Monoclonal antibodies against tumor necrosis factor alpha have altered mood in depressed patients with high basal levels of inflammation, and humanized anti-interleukin-6 receptor antibodies are currently under consideration for unipolar and bipolar depression.
For now, however, translating these neurofunctional discoveries directly into bedside care remains a distant goal.
In the long run, investigators aim to link patient symptoms directly with neural functioning. If successful, brain activity measurements could eventually help clinicians identify suitable therapies much faster than current practices, which rely largely on trial and error.