Effects of conditioned pain modulation on the withdrawal pattern to nociceptive stimulation in humans ? Preliminary results

F. A. JURE; F. G. ARGUISSAIN; J. A. BIURRUN MANRESA; O.K. ANDERSEN

Aalborg

Encuentro; SASP Annual Meeting 2017; 2017

Scandinavian Association for the Study of Pain SASP

AimsConditioned pain modulation (CPM) is a paradigm employed to assess descending control of spinal nociception. Previous studies have shown that CPM affects the nociceptive withdrawal reflex (NWR) threshold (RTh), typically assessed in one muscle. However, the NWR activates not one but a group of synergistic muscles, which are recruited by common neural commands to achieve the limb withdrawal. In this regard, synergy analysis can provide the minimum coordinated recruitment of groups of muscles with specific activation balances that describe a movement. The aim was to assess how CPM modulate the global withdrawal strategy of the lower limb expressed by synergy analysis.MethodsSixteen healthy subjects received electrical stimulation in the arch of the foot at 2 × RTh intensity assessed at the biceps femoris muscle, to elicit the NWR at three time points: before, during and after immersion of the hand in cold water at 2.6 ± 0.4° (cold pressor test, CPT) to trigger CPM. Electromyographic signals (EMG) were recorded from 2 distal muscles (tibialis anterior, soleus) and 2 proximal muscles (biceps femoris, rectus femoris). Muscle synergies were identified by a non-negative matrix factorization algorithm for the EMG envelope in the 60?180 ms post-stimulus interval. Data were analyzed by a point-by-point Wilcoxon test using a permutation strategy.ResultsThe overall withdrawal pattern was explained by two main synergies (Syn1 and Syn2). Syn1 mainly contributes to EMG of distal muscles, whereas Syn2 contributes to EMG of proximal muscles. During CPT, the magnitude of Syn2 was reduced in the 160?180ms post-stimulus interval (p < 0.05), whereas no changes were found for Syn1.ConclusionsAt least two synergies are required to explain the NWR. Furthermore, results suggest that CPM might differentially affect proximal and distal muscles. Further analysis is needed to provide additional information about the behavior of the individual muscles.