As two people with considerably different symptoms may receive the same depression diagnosis, researchers wanted to determine whether this individuality also manifests in brain activity.
According to the World Health Organization (WHO, 2025), depression affects roughly 332 million (5.2%) adults globally. In Finland, depression is the most common single cause of both prolonged absences due to illness and disability pensions.

Researchers at the University of Helsinki measured brain activity in 263 people with major depressive disorder and 75 healthy control subjects.
The analysis identified five groups where functional connectivity between brain regions differed. This connectivity reflects how effectively the regions function simultaneously, mirroring communication between the regions.

“What was particularly interesting was the contrasting patterns of brain activity found under the umbrella of the same depression diagnoses. In some individuals, the functional connectivity between brain regions was stronger than usual, while in others it was weaker,” says Director Satu Palva of the Neuroscience Center, University of Helsinki.

One of the groups was distinguished by particularly strong inter-region connectivity, which was associated with more severe substance abuse. In another group, where functional connectivity between regions was weak, post-traumatic stress disorder was emphasised among symptoms.

This finding may explain the partly conflicting findings of previous depression studies. The same diagnosis may be based on even entirely opposite changes in brain activity.
The finding supports the idea that depression is not a biologically similar disease for everyone.

Five brain profiles for depression
The researchers divided the depression patients into five groups according to the strength and frequency of connectivity between brain regions.

Group 1. Fairly strong connectivity between brain regions. Broadly severe symptoms, with depression, anxiety, rumination and reduced functional capacity pronounced.
Group 2. Weak connectivity between brain regions. Symptoms milder compared to other groups.
Group 3. Weak connectivity between brain regions in a large part of the brain. PTSD a particularly pronounced symptom.
Group 4. Varying connectivity between brain regions; some connections were weak, others strong. Depression severity, substance abuse and poor wellbeing as pronounced symptoms.
Group 5. Strongest connectivity between brain regions among the groups. Substance abuse a pronounced symptom, with fewer traumatic symptoms than in other groups.

All five groups also differed from healthy control subjects. The difference was evident not only in the intensity of connectivity, but also in the brain regions affected and the frequency at which the connectivity occurred.

Brain activity recorded with millisecond precision
The researchers used magnetoencephalography (MEG) to measure brain activity in 263 people with depression and 75 healthy control subjects. MEG measures weak magnetic fields generated by electrical activity in 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. Previously, depression phenotypes have been studied using methods with slower responses,” Palva notes.

Towards increasingly precise care
However, brain measurement is not enough to assign the appropriate treatment for individual patients.
“We’re not yet at the point where brain measurements can be used to choose the right treatment for patients, but the study does show one possible route,” Palva says.
In the long run, the goal is to link patients’ symptoms with how their brains function.
In the future, brain activity measurements could help identify suitable therapies faster than the current practice relying more on trial and error.

The research was carried out in collaboration with Aalto University and Helsinki and Uusimaa Hospital District (HUS).