Brain Mechanisms of Stress-Induced Analgesia: Exploring the Relationship Between Pain and Stress

Abstract

Despite several decades of research into the pain-suppression phenomenon of Stress-Induced Analgesia (SIA), mediated by biological and psychological factors, little is known about the underlying role of stress in pain perception. Previous research has established that stress plays an important role in the modulation of pain perception. This research focuses on how pain is modulated by stress, through a different perspective than used in earlier studies. The present study tested the hypothesis that psychological stress leads to a decreased perception of pain through increased activation of theamygdala and orbitofrontal cortex, and decreased activation of the cortical pain network. Eight healthy adults (five females and three males) were given painful heat stimuli before and after they performed a computerized task, and then underwent an fMRI scan. Subjects participated in (1) a control session in which the task was not stressful and (2) an experimental session on a separate day in which the task was stressful. When compared to the non-stress task, the stress task elicited increased activity during pain in the right amygdala (t = 2.43, p < 0.01) and the left dorsolateral prefrontal cortex (t = 3.64, p < 0.001), and reduced activity bilaterally in the thalamus (t = 5.09, p < 0.001), a key pain processing area; however, pain activity was not reduced significantly in the cortical pain network. These findings reveal new information about how stress can change the brain’s response to pain, leading to reduced perception.