Lippincott, Williams & Wilkins, PAIN, 3(155), p. 467-475
Human brain imaging investigations have revealed that acute pain is associated with co-activation of numerous brain regions, including the thalamus, somatosensory, insular and cingulate cortices. Surprisingly, a similar set of brain structures are not activated in all chronic pain conditions, particularly chronic neuropathic pain which is associated with almost exclusively decreased thalamic activity. These inconsistencies may reflect technical issues or fundamental differences in the processing of acute compared with chronic pain. The appreciation of any differences is important since better treatment development will depend on understanding the underlying mechanisms of different forms of pain. In this investigation we used quantitative arterial spin labeling to compare and contrast regional cerebral blood flow (CBF) patterns in individuals with chronic neuropathic orofacial pain (painful trigeminal neuropathy; PTN) and chronic non-neuropathic orofacial pain (painful temporomandibular disorder; TMD). Neuropathic pain was associated with CBF decreases in a number of regions, including the thalamus, primary somatosensory and cerebellar cortices. In direct contrast, chronic non-neuropathic pain was associated with significant CBF increases in regions that are commonly associated with higher order cognitive and emotional functions, such as the anterior cingulate and dorsolateral prefrontal cortices and the precuneus. Furthermore, in subjects with non-neuropathic pain, blood flow increased in motor related regions as well as within the spinal trigeminal nucleus.