This 2014 Japanese human study showed which brain areas were involved in indirect reciprocity.
The researchers found that it was mainly cerebral areas that were active in:
“Reputation-based reciprocity, in which they help others with good reputations to gain good reputations themselves.”
Previous studies found much the same with direct reciprocity, where an individual was reimbursed by someone who directly owed them a debt of cooperation.
It was mainly limbic system areas that were active in:
“Pay-it-forward reciprocity, in which, independently of reputations, they help others after being helped by someone else.”
The researchers thus compared and contrasted the self-interested behaviors of direct and reputation-based reciprocity, that sought rewards in the cerebrum, with the empathetic behavior of pay-it-forward reciprocity, which sought emotional rewards in the limbic system.
http://www.pnas.org/content/111/11/3990.full “Two distinct neural mechanisms underlying indirect reciprocity”