Researchers at Harvard found that the act of disclosing information about oneself stimulates the same pleasure centers in the brain that are activated by eating food, getting money and having sex. 

Part of the study monitored test subjects' brain reactions when answering questions about their own opinions and questions about other people's opinions.  Researchers found that the regions of the brain associated with reward - the nucleus accumbens and the ventral tegmental area - were triggered when people were talking about themselves and less engaged when they were talking about someone else. 

Researchers suggest that this is why roughly 80 percent of posts to social media sites are simply announcements of mundane but immediate experiences.