Functional Magnetic Resonance Imaging of Capsaicin-Induced Thermal Hyperalgesia

摘要

Most clinical pain is associated with increased sensitivity to external stimuli. In both inflammatory and neuropathic conditions, pain may be evoked by touch, pressure, movement, heat, or cold. Essentially, these phenomena represent reduced thresholds for eliciting pain and are termed allodynia, when pain is caused by innocuous stimuli, and hyperalgesia, when an exaggerated response follows application of a normally painful stimulus. Several animal models of neuropathic pain have been developed to investigate these pain syndromes (Devor and Seltzer 1999). Recent studies have described human pain models (Liu et al. 1998; Petersen and Rowbotham 1999) that share some characteristics of neuropathic pain and thus provide an opportunity to study clinical pain under controlled conditions. Our previous functional magnetic resonance imaging (fMRI) studies used intrinsically painful stimuli (thermal pain applied via a contact thermode) and healthy subjects, and thus primarily address physiological pain (Brooks et al. 2002). Results from these studies do not necessarily tell us much about clinical pain, in which multiple functional alterations occur in central and peripheral pain-signaling pathways.