25. Time profile of functional activation in the frontal and cingulate cortex during prolonged noxious stimulation: A preliminary fMRI study

Little is known about the temporal aspects of cortical activity during prolonged pain. In the present study, sixteen volunteers, aged 20-35 years, were studied by fMRI techniques. In the first group (Pain: n = 9), a dilute (20%, 0.5 ml) vitamin C solution was injected into the subcutaneous tissue of the dorsal aspect of a foot, resulting in a mild burning pain lasting some minutes. In the Control Group (n = 7), a non-noxious stimulation was applied. fMRI images were obtained from two adjacent paramedian sagittal planes, by a gradient-echo FLASH sequence (in-plane resolution = 1 mm; slice thickness = 5 mm; scan time 21 s), using a 1.5 T MR system. Fifty-eight images were acquired for each plane, beginning 5 minutes before and lasting 15 minutes after the onset of stimulation. Pixels whose signal time course was positively or negatively (r > 0.6 or < -0.6, respectively) correlated with the individual psychophysical curve of the intensity of perceived pain were found in the medial frontal pole and the anterior cingulate cortex, in the subjects of the Pain group experiencing a more severe pain. These findings support a role of selected cortical areas in pain perception.