psychotherapy:

Further research by Benedetti and others showed that the promise of treatment activates areas of the brain involved in weighing the significance of events and the seriousness of threats. “If a fire alarm goes off and you see smoke, you know something bad is going to happen and you get ready to escape,” explains Tor Wager, a neuroscientist at Columbia University. “Expectations about pain and pain relief work in a similar way. Placebo treatments tap into this system and orchestrate the responses in your brain and body accordingly.”

In other words, one way that placebo aids recovery is by hacking the mind’s ability to predict the future. We are constantly parsing the reactions of those around us—such as the tone a doctor uses to deliver a diagnosis—to generate more-accurate estimations of our fate. One of the most powerful placebogenic triggers is watching someone else experience the benefits of an alleged drug. Researchers call these social aspects of medicine the therapeutic ritual.