Recent work indicates that activity in the pain pathways of the brain exert an inhibitory influence on the perception of innocuous somatosensory stimuli. In our work this phenomenon was manifested as the inhibition of a somatosensory evoked potential (SEP) component whose amplitude is closely associated with innocuous somatosensation. This phenomenon has important implications for our understanding of how pain is coded at the cortical level and for establishing a quantitative and clinically practical method of measuring the function and integrity of the supraspinal pain pathways. Before these theoretical and clinical benefits can be realized, however, it will be necessary to demonstrate a close relationship between activity in the pain pathways and the inhibition of neurons involved in innocuous samatosensation. Toward this goal, we hope to demonstrate that: 1) The innocuous-related SEP component and the pain-related inhibition superimposed on it are generated in a cortical area that plays an important role in innocuous somatosensation (i.e., the primary somatosensory cortex). 2) The inhibition of innocuous- related somatosensory activity, as reflected in the SEP and subjective magnitude ratings, is specific to activation of the pain pathways. 3) There is a close relationship between the magnitude of activity in the pain pathways and the magnitude of SEP inhibition.
