Schematic diagram of important ascending and descending pathways of the nociceptive system. ACC Anterior cingulate; IC insular; MD mediodorsal; PAG periaqueductal gray; PC prefrontal; Po posterior thalamic nucleus; SI primary somatosensory; SII secondary somatosensory; VL nucleus ventralis lateralis; Vmpo nucleus ventralis medialis, posterior division; VPL nucleus ventralis posterior lateralis; VPI nucleus ventralis posterior inferior.