Talking about ourselves—whether in a personal conversation or through social media sites like Facebook and Twitter—triggers the same sensation of pleasure in the brain as food or money, researchers reported Monday.

About 40% of everyday speech is devoted to telling others about what we feel or think. Now, through five brain imaging and behavioral experiments, Harvard University neuroscientists have uncovered the reason: It feels so rewarding, at the level of brain cells and synapses, that we can't help sharing our thoughts....