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.

Investigation of threshold and magnitude criteria of the nociceptive blink reflex.

OBJECTIVE: The nociceptive blink reflex is a trigeminofacial brain-stem reflex which is used in pain research to evaluate the modulation of pain processing. To standardize the analysis of the reflex we investigated which electromyographic parameters show the best correlation with subjective pain ratings and should therefore be used for scoring blink reflex magnitude. Furthermore we investigated which parameters show the highest accuracy and reliability to define the blink reflex threshold. METHODS: Forty-six subjects each received 54 electrical stimuli to the supraorbital nerve at nine different stimulus intensities, which corresponded to pain ratings between 0 and 70 (scale 0-100). Multilevel modeling was performed to determine which electromyographic blink reflex parameter showed the best correlation with subjective pain ratings. To define the blink reflex threshold ROC analyses were performed, comparing different electromyographic blink reflex parameters with the judgment of expert raters for 2500 blink reflex recordings from this study and 1400 from another. RESULTS: The baseline-adjusted area under the curve showed the best correlation with subjective pain ratings. Seventy-six percent of the residual variance of the pain ratings could be explained by this parameter. The peak z score showed the highest accuracy in defining the blink reflex threshold and also the highest cut-point stability. CONCLUSIONS: We recommend the baseline-adjusted area under the curve for scoring the magnitude of the nociceptive blink reflex and the peak z score to define the nociceptive blink reflex threshold. SIGNIFICANCE: The here defined standardized criteria to score blink reflex magnitude and threshold improve the comparability and validity of blink reflex studies.