Evaluation of Endogenous Pain Modulation Mechanisms With Transcutaneous Electrical Nerve Stimulation

A number of chronic pain conditions are characterized by imbalances in excitatory and/or inhibitory mechanisms and these deficits appear correlated with the response to certain treatments. Evaluating these mechanisms among people who suffer from chronic pain could allow clinicians to adapt the treatment to each patient according to the deficits observed. To evaluate excitatory and inhibitory mechanisms, a thermode (hot plate) and a cold water bath can be used (standardized protocol). Unfortunately, these tools are expensive, time-consuming and require complex equipment and software. As such, it is not realistic for clinicians to use them for routine patient assessment. A potential alternative to study these mechanisms is TENS (transcutaneous electrical nerve stimulation). TENS is frequently used in rehabilitation and unlike thermode and cold water bath, is affordable, easy to use and requires very little time and equipment. The objective of this study are to determine if the TENS can replace the thermode and cold water bath (standardized protocol) for the evaluation of excitatory and inhibitory mechanisms. Also, to determine if there will be a correlation with the standardized protocol. 50 healthy participants between 18 and 60 years old will participate in this study. Each participant will attend two experimental sessions. In one of the two sessions, the evaluation will be done with the TENS; in the other session, the evaluation will be done with the standardized protocol (thermode and cold water bath).

To evaluate excitatory and inhibitory mechanisms, the investigators will used the modified CPM testing procedure consisting of test stimulus (TS) administered before and after a conditioning stimulus (CS). For the standardized protocol, the TS will consisted of a noxius heat stimulus generated by a thermode (hot plate), applied for two minutes on the non-dominant anterior forearm. The CS will consisted of a cold pressor test (CT), wherein participants immersed their dominant forearm in a cold water bath for two minutes. For the TENS protocol, the TS will consisted of a noxius electrical stimulus generated by TENS, applied for 5 seconds on the non-dominant knee at a frequency of 1 Hz and 5 Hz. The CS will consisted of a noxius electrical stimulus generated by TENS' applied for 120 seconds on the non dominant knee and ankle at a frequency of 2 Hz.