Assessing the Relationship Between Proposed Psychological and Neurobiological Mechanisms for the Placebo Effect and Hypnosis: A Review

Abstract

Purpose: Mental processes, such as those involved in the placebo effect and hypnosis, can lead to clinical improvements like analgesia. Comparing the psychological and neurobiological mechanisms behind the placebo effect and hypnosis can help clarify the relationship between these processes. Methods: A targeted Medline and Google Scholar literature review of publications written in English was performed, using the following key words: “placebo mechanisms,” “placebo neurobiology,” “hypnosis mechanisms,” “hypnosis neurobiology,” “hypnosis theories,” from 1945 to January 2016. Results: The placebo effect and hypnosis potentially share several psychological mechanisms, including expectations, evaluation of physical and interpersonal context, anxiety reduction, motivation, reward, and somatic focus. Neurobiologically, placebo and hypnotic analgesia have been shown to modulate key areas of the “pain matrix,” including the prefrontal cortex, the anterior cingulate cortex, the insula, the somatosensory cortices, the thalamus, and the midbrain. Conclusions: Given the several shared psychological and neurobiological mechanisms underlying the placebo effect and hypnosis, they may at times appear to be the same. However, the variety of placebo effects and hypnotic responses differ sufficiently in psychological, phenomenological, and neurobiological ways to suggest that they are different mental processes. These findings have important clinical and research implications.