Tor Wager
Professor of Psychology and Neuroscience, Institute for Cognitive Science, University of Colorado, Boulder

Placebos, expectations, and self-fulfilling prophecies

Placebo effects are improvements in signs and symptoms caused by the context in which a treatment is delivered.  They are a natural part of the way our brains work; their mechanisms include learning and neuroplasticity, emotion, social cognition,  and future-oriented cognition (i.e., prospection and expectation).  Clinically, placebo treatments tap into psychological “common factors” that are harnessed by wise therapists across many psychotherapeutic traditions.

However,  not all placebo effects are equally efficacious.  Though it is relatively easy to influence patients’ symptom reports, demonstrations of placebo effects on pathophysiology with meaningfully large effect sizes are rare.  Our work over the last years has explored some of the factors that create large and durable placebo effects on symptom-related brain physiology.  A working hypothesis is that strong placebo effects arise from the interaction between expectations and lived experience (i.e., reinforcement). Reinforcement induces learning and neuroplasticity in the brain systems that govern motivation and control over bodily physiology, and expectations guide what is learned from experience.  During this process, two mechanisms are crucial for creating durable effects. First, symptoms assimilate towards learned expectations; and (2) there is a confirmation bias in learning, such that symptoms congruent with expectations have more influence on learning that incongruent symptoms. Together, these two mechanisms can create self-reinforcing placebo effects that are resistant to extinction. Psychological and biobehavioral therapies are not yet designed with these principles in mind.  Advances in the science of placebo effects thus provides an opportunity to design a new generation of more effective forms of therapy.



Tor Wager is Professor of Psychology, Neuroscience, and Cognitive Science at the University of Colorado, Boulder. As of July 2019, he is joining the faculty of Dartmouth College as the Diana L. Taylor Distinguished Professor in Neuroscience. He received his Ph.D. from the University of Michigan in Cognitive Psychology in 2003, and served as an Assistant and Associate Professor at Columbia University from 2004-2009. Since 2004, he has directed the Cognitive and Affective Neuroscience laboratory, a research lab devoted to work on the neurophysiology of affective processes—pain, emotion, stress, and empathy—and how they are shaped by cognitive and social influences. Dr. Wager and his lab are also dedicated to developing analysis methods for functional neuroimaging and sharing ideas, tools, and scientific data with the scientific community and public.

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