"The brain can be made to drug itself, as seems to happen with certain placebos. We don’t merely imagine that the placebo antidepressant is working to life our sadness or worry—the brain is actually producing extra serotonin in response to the mental prompt of swallowing a pill containing nothing but sugar and belief. What all this suggests is that the workings of consciousness are both more and less materialistic than we usually think: chemical reactions can induce thoughts, but thoughts can also induce chemical reactions."