Understanding the placebo effect. Part 2: underlying psychological & neurobiological processes

Placebo and nocebo effects are interesting and complex phenomena. In this article, I discuss some findings about the psychological and neurobiological processes that may underlie these effects on the basis of studies of pain, Parkinson's disease, and depression. From a psychological perspective, expectancy and conditioning theories have been used to explain placebo and nocebo effects. These psychological processes may be translated into physiological effects through overlapping brain circuits that are important for cognitive information processing, analgesia, and reward expectations. These brain circuits may represent a fundamentally important common underlying pathway that mediates placebo and nocebo effects in many conditions. Understanding these effects is important for designing clinical treatment studies and interpreting their results and is highly relevant for clinical practices.