Cortical correlates of perception and suppression of electrically induced pain

Two neuroimaging studies using fMRI were conducted in order to assess the cortical processes involved in the perception and suppression of pain. In the first study, 15 healthy subjects were stimulated with variable intensities of electrical pulses during a discrimination task. In the second study, the same subjects had to try to suppress the feeling of pain during tonic stimulation. The discrimination task resulted in cortical activation of contralateral SI, corresponding in extent to the intensity of the stimulus. Activation of contralateral operculum/posterior insula (SII) and non-dominant dorsolateral prefrontal cortex (DLPFC) with non-painful stimuli changed to activations of non-dominant anterior insula upon painful stimulation. In the second study, all subjects succeeded in suppressing the feeling of pain during previously painful levels of stimulation. During this suppression task, activations changed from anterior to posterior insula; also there was a suppression of activity in the anterior cingulated cortex (ACC) and caudate nucleus. Subjects seem to be able to suppress to a certain degree the feeling of pain under constant (and previously painful) stimulation. The cortical correlate seems to be a shift of cerebral activation from anterior to posterior right insula and a suppression of activity in the ACC and caudate nucleus.