Pain is a multidimensional conscious experience including sensory and affective components.The former has been extensively studied,while the latter is poorly understood.Accumulating evidence from morphological,electrophysiological,neuroimaging,and behavioral studies as well as clinical observations indicated that the anterior cingulated cortex (ACC) is a key structure that contributes to pain negative affect or unpleasantness.Activation of ERK (extracellular signal-regulated kinase),a member of MAP (mitogen-activated protein) kinase family,in dorsal horn neurons of the spinal cord by peripheral noxious stimulation contributes to both short-term and long-term pain hypersensitivity.