In that kinship, friendship alliances, and perceptions of others’ beliefs guide social interactions and are central to cohesive group behavior, Fenna M. Krienen, from Harvard University (Massachusetts, USA), and colleagues studied how the medial prefrontal cortex region of the brain processes social information.

The researchers found that people’s brains are more responsive to friends than to strangers, even if the stranger has more in common, thereby suggesting that social alliances outweigh shared interests. The team’s findings affirm the hypothesis that certain regions of the brain process the social relevance of the person (closeness) to oneself and contribute to the assessment akin to signals that govern behavioral approach responses.

[Fenna M. Krienen, Pei-Chi Tu, Randy L. Buckner. “Clan Mentality: Evidence That the Medial Prefrontal Cortex Responds to Close Others.” J. Neurosci., Oct 2010; 30: 13906–15.]