Neurophysiology of Pain, Depression, and Exogenous Opioids

This chapter describes the intricate relationship between chronic pain and depression, particularly focusing on the underlying neurophysiological mechanisms connecting these comorbid conditions. Initially, the text highlights five hypotheses explaining the intertwined nature of pain and depression, with a deeper look into the common pathogenetic mechanisms hypothesis. This hypothesis emphasizes the shared neurophysiological pathways, primarily serotonin and norepinephrine. The text continues to describe the role of chronic opioid use in potentially exacerbating the link between pain and depression. It elaborates on the consequent neuroanatomical changes and the disruption of opioid receptors which may lead to emotional dysregulation, aberrant reward processing, and, eventually, depressive symptoms. Furthermore, it discusses how chronic opioid use impacts hedonic capacity, exacerbating the interplay between pain and depression. Finally, the text concludes by discussing the need for a more nuanced understanding of the underlying neurobiological interactions between pain and depression to better address these often comorbid conditions.