Abstracts
Résumé
Un placebo est un comprimé, un liquide ou une injection administrés en pharmacologie comme témoin de l’activité d’un médicament. Dans de très nombreux cas, ce produit inactif semble induire des effets biologiques ou psychologiques chez l’humain. Deux interprétations ont été envisagées : l’une propose que l’effet du placebo est une réponse conditionnée de type pavlovien, l’autre qu’il est en relation avec l’attente d’une réponse au traitement. Les mécanismes impliqués dans ces effets commencent seulement à être élucidés grâce à de nouvelles techniques d’investigation en neurosciences, notamment à l’imagerie cérébrale. La dopamine et les endorphines ont clairement été identifiées comme médiateurs des effets placebo. Ceux-ci s’accompagnent de modifications semblables à celles observées après administration du médicament, et cela dans les mêmes aires cérébrales. C’est le cas pour le placebo-dopamine dans la maladie de Parkinson, le placebo-analgésique, le placebo-antidépresseur et le placebo-caféine chez le sujet sain. Le problème reste de comprendre comment le conditionnement ou l’attente de la réponse peuvent activer, dans le cerveau, des circuits mémorisés reproduisant la réponse biologique attendue.
Summary
A placebo is a sham treatment such as pill, liquid, injection, devoid of biological activity and used in pharmacology as a control for the activity of a drug. In many cases, this placebo induces biological or psychological effects in the human. Two theories have been proposed to explain the placebo effect : the conditioning theory which states that the placebo effect is a conditioned response, and the mentalistic theory for which the patient expectation is the primary basis of the placebo effect. The mechanisms involved in these processes are beginning to be understood through new techniques of investigation in neuroscience. Dopamine and endorphins have been clearly involved as mediators of the placebo effect. Brain imaging has demonstrated that the placebo effect activates the brain similarly as the active drug and in the same brain area. This is the case for a dopamine placebo in the Parkinson’disease, for analgesic-caffeine- or antidepressor-placebo in the healthy subject. It remains to be understood how conditioning and expectancy are able to activate, in the brain, memory loops that reproduce the expected biological response.
Appendices
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