This project addresses issues relevant to the cerebral substrates of somesthetic perception, both in healthy human beings and those with an abnormal sensitivity to pain (allodynia and hyperalgesia). Neuroanatomical and neurophysiological studies in mammals, including human beings, have identified a number of cerebral structures that receive and process somesthetic input originating from the body, including: the post-central gyrus (primary somatosensory cortex- S1), the posterior parietal operculum (which includes the secondary somatosensory cortex - S2), the insula, and portions of the anterior cingulate cortex. These brain regions may play complementary roles for our somesthetic perceptions, including pain perception. Specifically, the S1 and S2 regions of cortex are proposed to be primarily involved with processing related to the discriminative aspects of perception, such as distinguishing the intensive or spatial features of stimulation. In contrast, the insular and anterior cingulate lesions, being anatomically related to the limbic system, are proposed to be primarily involved with the affective or emotional aspects of perception. The goal of this project is to use functional magnetic resonance imaging (fMRI) techniques and quantitative psychophysics to determine the cerebral activation patterns associated with various somatosensory stimuli, and to determine whether certain patterns of brain activation are reliably and specifically related to particular features of somesthetic experience. One specific hypothesis is that the aforementioned somatosensory cortical regions will show stimulus intensity-dependent responses for both mechanical and thermal stimuli. A second hypothesis is that the fMRI responses within S1 and S2 cortices will show better correlations with the subject's perceived intensity vs. their affective perception of thermal stimuli, and that the insular and anterior cingulate regions will show the opposite trend. Initially, these fMRI-measured cerebral response patterns will be examined in healthy individuals under normal conditions. Subsequently, we plan to follow-up this work with evaluations of individuals with allodynia and/or hyperalgesia associated with central pain. In this manner, this project will identify the cerebral response patterns to tactile, thermal, and painful stimuli, both in the neurologically normal and the chronically perturbed somatosensory system. It is anticipated that the results from this project will enhance our knowledge of how the brain processes pain-related information in humans, and of the extent to which differences in such processing occur in normal vs. pathological conditions.
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