Conditioned pain modulation is minimally influenced by cognitive evaluation or imagery of the conditioning stimulus

Figures & data

Figure 1 Experimental outline – task flow.

Notes: All tasks with “*”are 120 seconds long and were applied to the right foot. During the last 30 seconds of the 120 seconds, the Heat-50 (test stimulus) is applied to the left hand. The rating of the repeat Heat-5 occurs at the end of the 30 seconds. Task #1 refers to pre-cold water exposure imagery, and task #2 refers to post-cold water exposure imagery.
Abbreviation: CPM, conditioned pain modulation; min, minutes.

Table 1 Individualized temperature settings for the test and conditioning stimulia

Subject ID	Heat-5 (°C)	Cold bath temperature (°C)
02	46.5	16
03	48	8
04	44	16
05	48.9	8
06	48.9	16
07	46	8
08	45.4	8
09	45.5	12
11	45.6	8
12	47.5	8
14	47.3	8
15	43.5	12
16	46.5	8
17	46.3	8
19	44.5	16

Notes:

a We used Heat-5 as the test stimulus, applied via a Medoc contact heat-evoked potential stimulator thermode to the left palm during the last 30 seconds of the application of conditioning stimulus. We used a cold water bath as the conditioning stimulus, applied to the entire right foot for 2 minutes.

Figure 2 Cold water pain ratings for evaluation of the cold water.^a

Notes: ^aWe failed to find a significant difference in the rating of the conditioning stimulus between baseline and threatening or reassuring conditions, t(27.6)=−0.77, P=0.45. However, reassurance was significantly less than threatening, t(25.2)=−2.58, P=0.02. *The reassuring condition was significantly different from the threatening condition but neither was significantly different from no evaluation.

Figure 3 Heat test pain ratings for evaluation of the cold water.^a

Notes: ^aWe failed to find any difference in the post-conditioning rating of the test stimulus among no evaluation, threatening, or reassurance. Hence, evaluation did not affect the magnitude of conditioned pain modulation (CPM), which is calculated by subtracting the post-conditioning rating from the baseline rating of the test stimulus, F(2, 28.5)=0.70, P=0.50. *The difference was statistically significant between the baseline pain rating and any of the post-conditioning pain ratings of the test stimulus, regardless of the presence and mode of evaluation.

Figure 4 Pain ratings for baseline heat test, heat test with imagery conditioning, and heat test with cold water conditioning.^a

Notes: ^aWe did not find a significant effect of imagery conditioning on the pain rating of the test stimulus. In contrast, cold water conditioning resulted in significant reduction in the pain rating of the test stimulus, t(86.4)=−2.76, P=0.01. However, there was no significant difference in heat test pain ratings for the cold pain imagery trials as compared with baseline, t(75.8)=1.54, P=0.13, or from CPM trials, t(65.3)=−1.81, P.0.08. *Cold water conditioning resulted in a significant reduction in the pain rating of the pain stimulus, whereas the pain rating from imagery conditioning was not significantly different from either the baseline or the cold water conditioning.