Functional magnetic resonance imaging (fMRI) responses to painful pressure applied to the left thumb in patients with fibromyalgia and healthy control subjects. The top left graph shows mean pain rating plotted against stimulus intensity for the experimental conditions. In the 'patient' condition, a relatively low stimulus pressure (2.4 kg/cm2) produced a high pain level (11.30 ± 0.90), shown by the red triangle. In the 'stimulus pressure control' condition, shown by the blue square, administration of a similar stimulus pressure (2.33 kg/cm2) to control subjects produced a very low level of rated pain (3.05 ± 0.85). In the 'subjective pain control' condition, shown by the green square, administration of significantly greater stimulus pressures to the control subjects (4.16 kg/cm2) produced levels of pain (11.95 ± 0.94) similar to the levels produced in patients by lower stimulus pressures. The remainder of the figure shows common regions of activation in patients (red) and in the 'subjective pain control' condition (green), in which the effects of pressure applied to the left thumb sufficient to evoke a pain rating of 11 (moderate) is compared to the effects of innocuous pressure. Significant increases in the fMRI signal resulting from increases in regional cerebral blood flow are shown in standard space superimposed on an anatomical image of a standard brain (MEDx, Medical Numerics, Inc. 20410 Observation Drive, Suite 210, Germantown, Maryland 20876 USA). Images are shown in radiological view with the right brain shown on the left. Overlapping activations are shown by yellow. The similar pain intensities, produced by significantly less pressure in the patients, resulted in overlapping or adjacent activations in contralateral primary somatosensory cortex (SI), inferior parietal lobule (IPL), secondary somatosensory cortex (SII), superior temporal gyrus (STG), insula, putamen, and in ipsilateral cerebellum. The fMRI signal was significantly decreased in a common region in ipsilateral SI. Modified from Gracely and colleagues [33].