Comparison of trigeminal and spinal modulation of pain and nociception.

Modulation of pain and nociception by noxious counterstimulation, also called "diffuse noxious inhibitory controls" or DNIC-like effect, is often used in studies of pain disorders. It can be elicited in the trigeminal and spinal innervation areas, but no study has previously compared effects in both innervation areas. Therefore, we performed a study comparing DNIC-like effects on the nociceptive flexion reflex (NFR) and the nociceptive blink reflex as well as the respective pain sensations. In 50 healthy volunteers, the blink reflex elicited with a concentric electrode and the NFR were recorded before and after immersion of the contralateral hand in cold water. Responses were recorded as the subjective pain sensation and the reflex size. The cold water immersion of the contralateral hand elicited a reduction of both subjective pain sensation and reflex amplitude following the stimulation of both reflexes. However, there were no strong correlations between the individual reductions of both subjective pain sensation and reflex amplitude for both reflexes, and neither when results of the two reflexes were compared with each other. The dissociation between DNIC-like effects on pain and on nociception, which had been found previously already for the NFR, implies that both effects need to be studied separately.