Normative values of the nociceptive blink reflex habituation

To assess the habituation of nBR, 26 consecutive stimuli were administered at three different and randomized stimulus frequencies (0.2, 0.3, 0.5 Hz). The stimulation intensity of the habituation study was equal to 1.5 times the RTh. Of these stimulations, the first sweep was removed from the analysis to eliminate the startle response. The remaining 25 electromyographic were used to assess the habituation phenomenon. In offline analysis, for each electromyographic sweep the area under the curve (AUC) of the R2 component was manually measured and expressed in µV x ms. The obtained 25 AUC were divided in 5 blocks, and the average values of the AUC was calculated for each block. The habituation phenomenon was assessed with absolute AUCs values of the 5 blocks (µV x msec) as well as with AUC expressed as percentage variation from the first block of stimulation (normalized to 100%).

The percentage reduction in the AUC of the fifth block, compared to the first, represents the "habituation index" (HI) value. Thus, high HIs indicate a pronounced habituation, while low HI are indicative of a weak habituation phenomenon. Between the three different stimulus frequencies, participants waited at least 20 minutes to avoid a carry-over effect.