Journal of neurophysiology
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Comparative Study
Regional intensive and temporal patterns of functional MRI activation distinguishing noxious and innocuous contact heat.
Cortical responses to painful and nonpainful heat were measured using functional magnetic resonance imaging (fMRI) region of interest analysis (ROI) of primary somatosensory cortex (S1), secondary somatosensory cortex (S2), anterior cingulate (ACC), supplementary motor area (SMA), insula, and inferior frontal gyrus (IFG). Previous studies indicated that innocuous and noxious stimuli of different modalities produce responses with different time courses in S1 and S2. The aim of this study was to 1) determine whether temporally distinct nociceptive blood oxygen level-dependent (BOLD) responses are evoked in multiple somatosensory processing cortical areas and 2) whether these responses discriminate small noxious stimulus intensity differences. ⋯ Responses to innocuous and noxious stimuli were not statistically different in contralateral S2. In contralateral S1 only, the nociceptive response could differentiate heat stimuli separated by 1 degrees C. These results show that 1) multiple cortical areas have temporally distinguishable innocuous and noxious responses evoked by a painfully hot thermode, 2) the nociceptive processing properties vary across cortical regions, and 3) nociceptive responses in S1 discriminate between painful temperatures at a level unmatched in other cortical areas.