People with depression are more likely to feel bad in response to perceived inequality, according to a study published this week in Nature Human Behaviour. Simply, in experiments where participants were tasked with playing a game with a strong element of unfairness, those participants with higher levels of brain activity in depression-linked brain regions―as recorded via fMRI scans― were more likely to later demonstrate signs of clinical depression.

This is a new test of an old idea, one that's been demonstrated in previous research. People with depression commonly demonstrate increased concern for others, or for the perspectives of others. More precisely, prosocial attitudes predict depression, which is in contrast to individualist attitudes. Individualist here basically just means selfish, or relatively selfish.

The researchers behind the current study hypothesized that they would be able to observe these tendencies at the level of actual brain activity. Fortunately, there are some tried and true methods of testing prosocial behavior. One of these takes the form of what's known as an ultimatum game. The general idea is that participants are offered rewards that are to be shared among a group. Each offer differs in how much the participant gets in relation to the rest of the group, with prosocial participants more likely refuse larger personal rewards in favor of larger rewards going to everybody else. Individualists take the offer that best benefits them, while prosocial people are more concerned with other people in the group.

So, participants in the current study played a version of the ultimatum game while wired up to an fMRI machine. Some of them registered more activity in the amygdala and hippocampus regions of their brains―both of which tend to be smaller in people with depression―compared to other participants. The researchers then sat on this data, returning after a year had passed to see who wound up with higher markers for depression. The differences in later depression indicators could not be explained away by demographics.

The implication is that people with depression (or likely to have depression) generally have a "greater empathic concern for others," in the words of Megan Speer and Mauricio Delgado, psychology researchers from Rutgers University, who penned a related commentary accompanying the study. People with depression just feel bad when others get a shit deal.

A lot of people are getting a shit deal nowadays. More and more of them. That's the particular import of the study, according to its authors.

"Widening economic inequity has become an increasing concern for society and has been implicated as a source of several psychiatric diseases including depression," they write. "Previous large-scale cohort-based studies have indicated a link between economic gaps and major depression, where economic and material disadvantage are crucial in explaining depressive symptoms. Despite this importance, little is known about the neural mechanism that underlies the link between economic inequity and mood change."

This dawning world of radical inequality is probably bad news for those with depression, but, at the same time, it might be those same people that are best suited, psychologically speaking, to knock down that inequality.