The placebo effect is a phenomenon that has experienced major advances of its understanding in the last decade. However, mechanisms of placebo analgesia in chronic pain patients have yet to be compared to healthy subjects. The investigators study aims to investigate the magnitude of placebo response and related opioid release in patients that suffer from episodic migraines as compared to healthy controls. In particular, the investigators are looking to map brain activity during placebo analgesia using modern brain imaging techniques such as functional Magnetic Resonance Imaging (fMRI) and Positron Emission Tomography (PET). The investigators hypothesis is that placebo response and the availability of opioid receptors is reduced in chronic migraine patients.