Abstract
Some economic transactions require people to trust strangers, whose trustworthiness is unknown. In these circumstances, behavioral studies have shown that adults (but not young adolescents) seem to have some minimal ability to detect the trustworthiness of adult strangers based on their facial features. In this study, we explored the neural correlates of this facial trustworthiness detection. A group of adolescents and adults played a series of economic Trust Games with adult trustees of which we had previously recorded the strategy. Results showed that when adult investors were looking at the picture of a trust-abusing trustee, the left amygdala was relatively more activated than when they were looking at a trust-honoring player. Younger adolescents did not show this pattern and responded with a more pronounced deactivation when facing a trust-abusing trustee. An exploratory whole-brain analysis detected a similar age shift for mentalizing regions of the brain. Our results fit with an emerging model suggesting that the amygdala is implicated in an associative learning process that progressively refines a mapping of faces onto trustworthy behavior and may result in avoiding to be exploited by untrustworthy strangers.