Placebo treatments: Historical overview and current concepts [L'effetto placebo come terapia: Storia e attualità]

The placebo effect is a widespread phenomenon in medicine and its neurobiological mechanisms are understood only partially. Insights on the brain mechanisms underlying the placebo effect come mostly from studies on pain conditions, including headache. In summary, placebo analgesia represents a situation where the administration of a substance known to be non-analgesic produces an analgesic response every time the subject is told that it is a painkiller. On the other hand, the nocebo effect is the phenomenon whereby a patient who believes that a treatment will cause harm actually experiences adverse effects. The discovery that placebo analgesia is mediated by the release of endogenous opioids - and nocebo hyperalgesia by the release of the neuropeptide colecystokinin - opened new avenues to our understanding of the neurobiology of brain-body interactions. Finally, placebo-induced expectations have proved able to trigger different neural pathways affecting not only perception, but also movement and mood, as shown by recent neuroimaging studies on patients affected by Parkinson disease and major depression.