Gender differences in pain perception and patterns of cerebral activation during noxious heat stimulation in humans

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Abstract
Al blood flow (rCBF) in normal right-handed male and female subjects as they discriminated differences in the intensity of innocuous and noxious heat stimuli applied to the left forearm. Each subject was instructed in magnitude estimation based on a scale for which 0 indicated ‘no heat sensation’; 7, ‘just barely painful’ and 10, ‘just barely tolerable’. Thermal stimuli were 40°C or 50°C heat, applied with a thermode as repetitive 5-s contacts to the volar forearm. Both male and female subjects rated the 40°C stimuli as warm but not painful and the 50°C stimuli as painful but females rated the 50°C stimuli as significantly more intense than did the males (P=0.0052). Both genders showed a bilateral activation of premotor cortex in addition to the activation of a number of contralateral structures, including the posterior insula, anterior cingulate cortex and the cerebellar vermis, during heat pain. However, females had significantly greater activation of the contralateral prefrontal cortex when compared to the males by direct image subtraction. Volume of interest comparison (t-statistic) also suggested greater activation of the contralateral insula and thalamus in the females (P<0.05). These pain-related differences in brain activation may be attributed to gender, perceived pain intensity, or to both factors....