Investigation of threshold and magnitude criteria of the nociceptive blink reflex

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.

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.

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.

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.

The here defined standardized criteria to score blink reflex magnitude and threshold improve the comparability and validity of blink reflex studies.