There are quite a few ways to explore conditioned pain modulation (CPM). It may be through a set stimulus with asking the participant to rate their pain, or with a stimulus that the participant will stop when it reaches their pain threshold.
In our featured article this time, the Swiss group from Balgrist University Hospital have used the “Search” program in the Medoc Main Station software with the Pathway device in order to obtain a participant-controlled pain stimulus.
The objective was for the participant to keep the tonic heat pain intensity equal (calibrated per person at about 50/100 VAS) by clicking the left and right mouse buttons (causing a temperature rise or drop, respectively). The conditioning stimulus consisted of a cold pressor.
The tonic heat pain temperature was used to measure adaptation (by a rise in participant-controlled temperature), and temporal summation (by a subsequent drop in participant-controlled temperature). The temperature was limited to 45 degrees by the program for participant safety.
An additional CPM test
In order to validate this method, two other test-stimuli were used during an additional CPM test: one with pressure pain threshold, and one with noxious withdrawal reflex.
Interestingly, this group was able to show that when the temperature was participant-controlled, there were no differences between men and women that are usually noted in using pain ratings. Moreover, the use of this paradigm showed that the CPM effect could diminish temporal summation irrespective of the pain ratings during the cold pressor test or the time since the conditioning stimulus.
These findings show a bright and new method to explore pain and pain modulation that is valid and participant-controlled. They point that participant controlled temperature eliminates the cognitive load of “translating” the level of pain to a numerical rating and may be more accurate and representative of the true sensation the participant experiences during this experimental pain paradigm.
How to use Medoc's Search program on the MMS
We created a short video to demonstrate how the Search program is to be used on Medoc Main Station:
Sirucek, L., Jutzeler, C. R., Rosner, J., Schweinhardt, P., Curt, A., Kramer, J. L. K., & Hubli, M. (2020). The Effect of Conditioned Pain Modulation on Tonic Heat Pain Assessed Using Participant-Controlled Temperature. Pain Medicine.