The Role of Sleep in Learning Placebo Effects

The placebo effect is a psychobiological phenomenon producing clinical benefits attributed to a wide range of neurobiological mechanisms. Independently from placebo effects, these mechanisms may also be under the influence of processes that can take place during sleep. The relationship between sleep and placebo effects has received very little attention. Three experimental studies, conducted on healthy subjects, have examined sleep changes following placebo conditioning associated with analgesic suggestions and the effects of sleep deprivation on placebo effects. A relation between rapid eye movement (REM) sleep, expectations of relief and placebo analgesia was observed in which REM sleep deprivation seems to improve placebo-induced expectations and analgesia. Moreover, analgesic expectations developed before sleep produced a reduction in cortical arousals evoked by noxious stimuli during REM sleep. In this article, we describe sleep and pain/analgesia interactions, the relationship between sleep and placebo analgesia, and finally the potential mechanisms underlying this relationship.