Plazebos in Klinik und Forschung: Experimentelle Befunde und theoretische Konzepte

Zusammenfassung

Die Plazeboresponse in Medizin und Psychologie ist bislang unzureichend erklärt und wird in der Regel entweder mystifiziert oder abgewertet; rationale Ansätze zum Verständnis der Plazebowirkung einer medizinischen oder psychologischen Intervention sind jedoch aus der bisherigen Literatur ableitbar. Wir diskutieren hier drei Theorien, die u. E. viele der beschriebenen Plazeboeffekte erklären können: a) Regression zum Mittelwert (regression to the mean, RTM): dies können „Messfehler” sein, die durch kleine Stichproben, globale abhängige Variablen, spontane Schwankungen der Symptomatik und andere methodische Gründe entstehen. b) Pavlovsche Konditionierung (PC): hier entsteht die Plazebowirkung z. B. über erfolgreiche Verknüpfung von Diagnose- und Therapiemaßnahmen in der Vergangenheit (Krankengeschichte) eines Individuums mit Symptombesserung. Neutrale Stimuli aus dem Umfeld der Behandlung wie die Art der Verabreichung einer Injektion oder die Farbe einer Tablette (konditionierte Stimuli) bekommen so eine therapeutische Potenz. c) Signalentdeckungstheorie (signal detection, SD): Die Manipulation von Erwartungen und Kognitionen der Patienten durch Suggestionen und verbale Instruktionen seitens des medizinischen Heilungssystems verändert die Bereitschaft der Patienten, Symptome als gebessert/verschlechtert zu betrachten, insbesondere dann, wenn dies auf dem Hintergrund eines hohen Rauschpegels geschieht, z. B. bei starken Spontanschwankungen der Symptome. Für alle drei theoretischen Modelle werden Beispiele aus der medizinischen und psychologischen Behandlung von Erkrankungen bzw. der experimentellen Forschung herangezogen, einschließlich neuerer Befunde zu kortikalen Korrelaten der Plazebowirkungen in funktionellen Bildgebungsuntersuchungen. Potenzielle biologische Mechanismen der Plazeboantwort werden diskutiert, einschließlich der Möglichkeit einer genetischen Prädisposition zum Plazeboresponder.

Abstract

The placebo response in medicine and psychology is incompletely understood, and is usually either mystified or down-played; a rational approach to the understanding of the placebo response, however, can be deduced from the scientific literature. We present 3 theories that may explain most of the placebo response in medical and psychological interventions: a) Regression to the mean (RTM): This refers to „errors” in measuring the outcome of therapies, that are due to small samples sizes, global assessment variables, spontaneous variability of symptoms, and other methodological reasons. b) Pavlovian Conditioning (PC): here the placebo response occurs as the consequence of successful association of diagnostic and therapeutic procedures in the past (illness history) of the individuum that resulted in symptom improvement. Neutral stimuli in the context of a treatment can thus gain therapeutic potency (become conditioned stimuli), e. g. the procedure of an injection or the colour of a drug. c) Signal detection theory (SDT): manipulation of expectencies and cognitions of the patient by suggestions and verbal instructions of the health care system will change the willingness of the patient to perceive symptoms as improved/worsened, specifically if this happens under „noisy” circumstances, e. g. with high spontaneous variability of symptoms. All three models are illustrated with examples from medical and psychological treatments or experiments, including recent findings of cortical correlates of the placebo response in functional brain imaging investigations. Potential biological mechanisms for the placebo response are discussed, including the possibility of genetic predisposition to be a placebo responder.

Key words

Placebo - Nocebo - functional bowel disorders - clinical trials

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1 Die Begriffe Arzt, Patient, Proband und Versuchsleiter sind geschlechtsneutral zu verstehen.