Brains with compromised 'trust settings' a sign of depression

Just as our devices acting differently can tip us off to the possibility of malware lurking in the background, changes in brain patterns that shape our trust behaviour can alert us to sneaking depression even before other symptoms appear. That’s according to a new study from Japanese researchers, led by Hiroshima University and published in the journal Scientific Reports.

Major depressive disorder (MDD), or clinical depression, is a pervasive mental health condition affecting millions worldwide. When severe signs of MDD are already visible, doctors can easily come up with a diagnosis. But at that stage, treatment can get more challenging as response to medications is reduced, thus requiring more aggressive interventions.

“Our question was: can we use social personality information to predict the development of mental disorders, such as depression?” said Alan SR Fermin, the corresponding author on the study.

Trusting is associated with the expectation of kindness and reciprocation of cooperation from others as well as compliance with social norms. However, trusting others is not an easy task as aversive social interactions are often observed in different environmental settings, such as bullying at school, harassment at work or even physical violence at home. Breach of trust and individual differences in trusting others have been shown to harm mental health as low trusters tend to isolate themselves from social interactions and, consequently, develop depression.

The researchers’ brain scans revealed that shrunken grey matter volumes in regions of the ‘social brain’ tied to a compromised trusting ability shared a connection with depression vulnerability that could help with its early detection. Their findings add to previous studies that showed a connection between trust and depression, while also uncovering the neuroanatomical basis of this relationship.

“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,” Fermin said.

“Overall, we found that the brains of lower trusters showed reduced grey matter volume in brain regions involved in social cognition. Also, we found that this grey 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.”

Structural neuroimaging analyses showed both low trust and high depressive symptoms are linked to reduced grey matter volumes in the brain’s bilateral angular gyrus, bilateral dorsolateral prefrontal cortex, bilateral dorsomedial prefrontal cortex, bilateral precuneus, ventromedial prefrontal cortex (right frontal pole and right rectus gyrus) and the left posterior cingulate cortex. Whole-brain voxel-based morphometry analysis of their study sample also showed that when trust levels dwindle, grey matter volume in the parahippocampus–amygdala region also shrivels. These are brain regions that help humans control their emotions, think, and predict others’ mental states and behaviours. Thus, the reduced volume of these brain regions in low trusters suggests possible disturbances in emotion control and in the estimation of others’ trustworthiness, which may contribute to the development of depression.

“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,” Fermin said.

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