The somatosensory system has by far the largest number of receptor types of any of the primate sensory systems, including mechanoreceptors, chemoreceptors, nociceptors and thermoreceptors. The sensation of touch is mainly mediated by mechanoreceptors, but there are a number of other processing channels within the somatosensory system for proprioception, pain and temperature. The classic view of two independent channels for somatosensory information from the trunk and the extremities, i.e. the dorsal column-medial lemniscus system for tactile sensitivity and position sense and the anterolateral or spinothalamic system for pain and temperature sensitivity, has been modified through the discovery of additional spinal pathways for the transmission of sensory impulses to the brain (Willis and Coggeshall 1991) and by new views on pain mechanisms. Somatosensory information from the face is transmitted via the trigeminal nerve. Pain is conventionally viewed as a submodality of cutaneous sensation. Functional, anatomical and imaging data suggest that pain impulses are conveyed by specific ­sensory channels that ascend in a central homeostatic afferent pathway (Craig 2003a, b).