Stimulus predictability modulates the withdrawal strategy to nociceptive stimulation in humans

F. A. JURE; F. G. ARGUISSAIN; J. A. BIURRUN MANRESA; T. GRAVEN-NIELSEN; O. K. ANDERSEN

Yokohama

Congreso; 16th World Congress on Pain; 2016

International Association for the Study of Pain IASP

Aim of Investigation The nociceptive withdrawal reflex (NWR) is elicited when a nociceptive stimulus is detected, and resulting in a withdrawal of the limb to prevent potential tissue damage. In this process, neural mechanisms, biomechanical strategies and muscular activity are integrated. Previous studies of modulation of lower limb NWR indicate that the NWR response is modulated by stimulation site, intensity, frequency, and by supraspinal activity like ongoing cognitive processes. The aim of the present study was to investigate the supraspinal modulation of the biomechanical withdrawal strategy of human lower limb reflexes due to the predictability of repetitive nociceptive stimulus.MethodsEleven healthy subjects participated in the study (six males, mean age: 25 years, range 20-35 years). NWRs were elicited by electrical stimulation at the arch of the foot. A stimulus consisted of a train of five constant-current pulses (1 ms duration, 5 ms interval) repeated three times at a frequency of 1 Hz (temporal summation). The interval between two trains was randomized between 10 s to 15 s. The NWR threshold (RTh) and the pain threshold (PTh) were determined using a standardized staircase procedure. Stimulation intensity for eliciting NWR was set to 1.2 times the PTh. The sessions consisted of one block of twelve trains in which the stimulation onset of the train was unpredictable, and one block of twelve trains in which an auditory cue was delivered 1 s before the train onset. Electromyographic signals (EMG) were recorded from the tibialis anterior (TA) and the biceps femoris (BF) muscles. NWR amplitudes were quantified as the root-mean-square value (RMS) of the EMG in both muscles in the 60 - 180 ms post stimulation interval. The probability of occurrence of a NWR was defined as the number of trials in which a NWR was detected divided by the total number of trials. Data from each muscle was analyzed using a two way repeated measures analysis of variance (ANOVA) with factors: condition (with and without cue) and stimulus number (first, second and third). The Greenhouse-Geisser was applied to account for deviations in sphericity, and the Tukey test was used for post hoc comparisons in case of significant main effect or interaction.ResultsThe mean RTh in TA was 6.2 mA (range 3.3 ? 9.5 mA), whereas the mean PTh was 13.2 mA (range 8.5 ? 24.5 mA). Results show a significant main effect of condition for NWR amplitude on the BF muscle (F1,10 = 6.16; p = 0.032), whereas no significant effects were found on the TA muscle. With regards to probability of occurrence, the ANOVA also showed significant main effect of condition for BF muscle (F1,10 = 7.35; p = 0.022), whereas no significant effects were found on the TA muscle.ConclusionThe predictability of the nociceptive stimulus modulates the biomechanical withdrawal strategy of the lower limb in humans. Thus, this study shows that the NWR from the BF muscle is larger and the probability is higher when the stimulus is unpredictable. On the other hand, the activity and the probability of eliciting NWR in the TA muscle remain unchanged in relation to the predictability. These results indicate that descending control plays a major role for the withdrawal reflex strategy and stimulation site is not the only predictor.