Socializing the amygdala

Personality differences which arise in relation to our feelings on inequality, modify activity in the amygdala ― a brain region important for automatic emotional processing. The study, published online this week in Nature Neuroscience, contradicts previous ideas which suggest that such personality differences are due to prefrontal cortex differences.

How people prefer to divide resources between themselves and others is a stable personality trait. Prosocial individuals, who typically work in ways that benefit others, prefer to maximize resources for themselves, but also like that others have similar resources. Individualists, however, prefer to maximize resources for themselves, regardless of the amount available for others.

The way in which people reach these types of decision has been debated but one theory is that an automatic, 'bottom up' response only considers the reward for oneself, and 'top-down' control ― thought to be exerted by the prefrontal cortex ― is required to overcome this selfish impulse.

Masahiko Haruno and Chris Frith tested the idea of 'top down' and 'bottom up' processing during sharing tasks by looking at how the brains of prosocial and individualistic people respond to the desirability of a pair of rewards ― one for themselves and one for a partner. They found that prosocial people did not like unfair scenarios and responded accordingly, whereas individualists' choices were not influenced how fair things were. The teams noted that activity in the amygdala differed between these two groups of people, with greater reward inequality correlating with greater amygdala activation in the prosocials. They therefore conclude that the characteristic prosocial aversion to inequality is linked to activity in the amygdala, and does not depend on top-down control of selfish impulses.