The parts of the brain linked to this trait were shrunken in people with depression vulnerability.
Displaying a lack of trust in others is an early sign of depression.
People who find it hard to trust — which is, after all, at the heart of social relations — are at a higher risk of developing major depressive disorder.
And neuroscientists have found that the part of the brain that processes trust-based information is shrunken in people with depression vulnerability.
Indeed, this change in the brain can predict the onset of depression one year in advance.
Trust requires a leap of faith
The conclusions come from a neuroimaging study that examined the gray matter volume of over 500 people in Japan.
Dr Alan S. R. Fermin, the study’s first author, explained the motivation:
“Our question was: Can we use social personality information to predict the development of mental disorders, such as depression?
Having tools that help identify early signs of mental disorders could accelerate medical or other therapeutical interventions.”
Being able to trust others is crucial, but it requires an expectation that others comply with social norms.
Unfortunately, the world is full of evidence that people are not trustworthy: there is gossip, bullying, harassment and violence in many places.
So, trust requires a leap of faith.
People who find it difficult to take this leap can become isolated and develop depression.
Dr Fermin said:
“In our study, we not only replicated the association between low trust and depression but also demonstrated that brain regions associated with trust were also associated with the degree of depressive symptoms one year in advance.
Overall, we found that the brains of lower trusters showed reduced gray matter volume in brain regions involved in social cognition.
Also, we found that this gray matter volume reduction among low trusters was similar to the brain of actual depressive patients.
Thus, even though our participants hadn’t received any diagnosis of depression, their brains were already showing signs of depression.”
Reduced gray matter volume
The brain scans revealed that people with high levels of depression symptoms and low levels of trust had reduced gray matter volume in a whole series of regions.
These regions are involved in how we control our emotions and predict other people’s mental states.
It is not yet known what causes these brain regions to shrink.
Dr Fermin said:
“We hope that our findings could support the development of institutional and social policies to increase social trust—for example, at work, school, or public space—and prevent the development of mental disorders.”
The study was published in the journal Scientific Reports (Fermin et al., 2022).
