Pain intensity processing within the human brain: A bilateral, distributedmechanism

Functional imaging studies of human subjects have identified a diverse asso rtment of brain areas that are engaged in the processing of pain. Although many of these brain areas are highly interconnected and are engaged in mult iple processing roles, each area has been typically considered in isolation . Accordingly, little attention has been given to the global functional org anization of brain mechanisms mediating pain processing. In the present inv estigation, we have combined positron emission tomography with psychophysic al assessment of graded painful stimuli to better characterize the multireg ional organization of supraspinal pain processing mechanisms and to identif y a brain mechanism subserving the processing of pain intensity. Multiple r egression analysis revealed statistically reliable relationships between pe rceived pain intensity and activation of a functionally diverse group of br ain regions, including those important in sensation, motor control, affect, and attention. Pain intensity-related activation occurred bilaterally in t he cerebellum, putamen, thalamus, insula, anterior cingulate cortex, and se condary somatosensory cortex, contralaterally in the primary somatosensory cortex and supplementary motor area, and ipsilaterally in the ventral premo tor area. These results confirm the existence of a highly distributed, bila teral supraspinal mechanism engaged in the processing of pain intensity. Th e conservation of pain intensity information across multiple, functionally distinct brain areas contrasts sharply with traditional views that sensory- discriminative processing of pain is confined within the somatosensory cort ex and can account for the preservation of conscious awareness of pain inte nsity after extensive cerebral cortical lesions.