Spatial and Temporal Characteristics of Pain Processing in the Human Brain

Contrary to the traditional view that the cerebral cortex is not involved in pain perception, an extensive cortical network associated with pain processing has been revealed during the past decades. This network essentially includes the primary (S1) and secondary somatosensory cortices (S2) and the anterior cingulate cortex (ACC). In a series of studies we investigated the spatial and temporal characteristics of pain processing within these cortical areas by using magnetoencephalography and selective nociceptive cutaneous laser stimulation. Time courses of activations show that within this cortical network the processing of pain is organized in a predominantly parallel mode. This parallel organizational mode of pain processing is distinct from the elaborated and mainly serial organization of tactile processing and may allow for fast and effective reactions to harmful stimuli. Stimulus-response functions of activations suggest that the different cortical areas differentially contribute to the multidimensional experience of pain. S1 is mainly involved in discriminative aspects of pain while S2 seems to have an important role in cognitive aspects of pain perception and the ACC has been shown to be closely related to pain affect. Furthermore, extending the analysis of pain processing to very late activations revealed different contributions of these areas to first and second pain sensation. First pain appears to be particularly related to activation of S1 whereas second pain is closely related to ACC activation. Both sensations were associated with S2 activation. These findings may reflect the different biological functions of first and second pain. First pain signals threat and provides sensory information for an immediate withdrawal whereas second pain may attract longer-lasting attention and initiate behavior to limit injury and optimize recovery. The analysis of interactions between processing of touch and pain show that pain facilitates processing of touch in S1 and S2 which may represent a physiological correlate of the attention-attracting property of pain. Taken together, these findings contribute to the fundamental understanding of pain processing in the human brain and may provide the basis for understanding and optimizing pain therapy.