Mechanisms of the placebo response.

The concept of placebo response has evolved in the past few years from the clinical trial setting and medical practice to a psychobiological model that gives us important information on how the patient's brain is modified by the psychosocial context around the therapy. In this review, some examples will be given where physiological or pathological conditions are altered following the administration of an inert substance along with verbal instructions tailored to induce expectation of a change, and explanations will be presented with details on neurotransmitter changes and neural pathways activated. Although nothing is known about the biological underpinnings of the placebo response in the respiratory system, this review may help extending the neurobiological investigation of placebos from conditions such as pain and Parkinson's disease to respiratory disorders and symptoms such as cough.