Activation of central sympathetic networks during innocuous and noxious somatosensory stimulation.

Although pain is accompanied by autonomic nervous system responses, the cerebral circuits involved in the autonomic pain dimension remain elusive. Therefore, we used functional magnetic resonance imaging (fMRI) and investigated brain processing associated with cutaneous sympathetic vasoconstrictor reflexes during noxious stimulation. When a classical fMRI analysis based on the applied block design was performed, we were able to detect activations well known to be engaged in the central processing of touch and pain. A parametric fMRI analysis in which cutaneous vasoconstrictor activity was correlated with MRI signals revealed two distinct patterns of brain activity. During (i) noxious stimulation itself, brain activity correlated with sympathetic activity in the anterior insula, ventrolateral prefrontal cortex (VLPFC), anterior cingulate cortex (ACC), and secondary somatosensory cortex (S2). During (ii) baseline, brain activity correlated with sympathetic activity in the VMPFC, dorsolateral prefrontal cortex (DLPFC), OFC, PCC, cuneus, precuneus, occipital areas, and hypothalamus. Conjunction analysis revealed significant similar responses during periods of noxious stimulation and periods of sympathetic activation in the anterior insula, ACC and VLPFC (activation) and VMPFC, OFC, PCC, cuneus and precuneus (deactivation). Therefore, we here describe a cerebral network which may be engaged in the processing of the autonomic subdimension of the human pain experience.