APA Dictionary of Psychology

any neural pathway that mediates sensations of pain. Afferent pain pathways include rapidly conducting myelinated A fibers and slowly conducting unmyelinated C fibers, ascending tracts in the anterolateral system, the periaqueductal gray matter, the reticular formation, and many thalamic and cerebral cortical areas, especially the cingulate cortex. There are also efferent pathways that inhibit pain signals at various levels down to spinal synapses, including release of endogenous opioids that inhibit pain.