Brain response to placebo (image) University of Michigan Health System Caption These images created from data gathered on PET scanners shows the areas of the brain where levels of natural mu-opioid painkillers rose in healthy volunteers who received a painful injection followed by a placebo. This response corresponded with certain personality traits. Credit Zubieta laboratory, University of Michigan Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.