Final Report Summary - PLACEBO (The placebo effect – a window into the relationship between mind and body)
In addition the findings of all these studies have prompted us to propose a unified framework underlying placebo/nocebo effects. Whereas, we initially hypothesized that simple reinforcement learning mechanisms are sufficient to explain placebo effects, we are now convinced that a more general model is better suited to capture the effects observed in placebo analgesia. In particular, we suggest that the ascending and the descending pain pathways resemble a recurrent system that allows for the implementation of predictive coding - meaning that the brain is not passively waiting for nociceptive stimuli to impinge on it, but is actively making inferences based on prior experience and expectations. The Bayesian aspect within the predictive coding framework can directly account for differences in the magnitude, but also the precision of expectations which are known to influence the strength of placebo hypoalgesia. Implicit in this model is also the assumption that modulatory neurotransmitters such as opioids might be related to the characterization of expectations with an emphasis on the precision of these expectations.