The cortical map of tactile sensation, the sensory homunculus, represents a fundamental aspect of our understanding of sensory processing, which dates to the time of Sherrington [6], and has been extensively studied in both humans [5] and animals [4]. Identifying the cortical representation of painful stimuli has proven considerably more challenging than for non-painful tactile stimuli. The pain experience is more complex and subjective in nature and there are difficulties inherent in presenting painful stimuli to people, and especially to animals. The subjective aspects of pain, including its psychophysical, cognitive, emotional and clinical features, have been investigated primarily in people, while the objective physiological mechanisms and anatomical substrates mediating pain have been investigated in a largely separate area of studies, conducted primarily in animals. The advent of neuroimaging has presented a new bridge for unifying these subjective and objective approaches, allowing investigation of the brain localization and physiological mechanisms of pain in both humans and animals.
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