[Placebo analgesia and sleep].

The placebo response is a psychobiological phenomenon for clinical benefits following the administration of an inert substance whatever its form. This phenomenon can be attributed to a wide range of neurobiological processes, such as expectations of relief, the Pavlovian conditioning and learning, emotional regulation, and reward mechanisms, which are themselves under the influence of processes that take place during sleep. The study of placebo analgesia in healthy from a placebo conditioning associated with analgesic suggestions has highlighted a relationship between sleep, expectations of relief and placebo analgesia: when the induction is persuasive before sleep, expectations of relief modulate placebo response the next morning and paradoxical sleep correlates negatively with both expectations and the placebo response. When the analgesic experience before sleep is less persuasive, expectations of relief are still present but no longer interact with placebo analgesia while paradoxical sleep no longer correlates with the analgesic placebo response. Sleep-processes especially during paradoxical sleep seem to influence the relationship between expectations of relief and placebo analgesia. In this review, we describe the relationship between sleep and placebo analgesia, the mechanisms involved in the placebo response (e.g., conditioning, learning, memory, reward) and their potential link with sleep that could make it a special time for the building placebo response.