Abstract
BackgroundConditioned pain modulation (CPM) evaluates the effect of a painful conditioning stimulus (CS) on a painful test stimulus (TS). Using painful cutaneous electrical stimulation (PCES) as TS and painful cold water as CS, the pain relief was paralleled by a decrease in evoked potentials (PCES-EPs). We now aimed to compare the effect of CPM with cognitive distraction on PCES-induced pain and PCES-EP amplitudes.MethodsPCES was performed using surface electrodes inducing a painful sensation of 60 (NRS 0–100) on one hand. In a crossover design healthy subjects (included: n = 38, analyzed: n = 23) immersed the contralateral hand into 10 °C cold water (CS) for CPM evaluation and performed the 1-back task for cognitive distraction. Before and during the CS and 1-back task, respectively, subjects rated the pain intensity of PCES and simultaneously cortical evoked potentials were recorded.ResultsBoth CPM and cognitive distraction significantly reduced PCES-EP amplitudes (CPM: 27.6 ± 12.0 μV to 20.2 ± 9.5 μV, cognitive distraction: 30.3 ± 14.2 µV to 13.6 ± 5.2 μV, p < 0.001) and PCES-induced pain (on a 0–100 numerical rating scale: CPM: 58 ± 4 to 41.1 ± 12.3, cognitive distraction: 58.3 ± 4.4 to 38.0 ± 13.0, p < 0.001), though the changes in pain intensity and PCES-amplitude did not correlate. The changes of the PCES-EP amplitudes during cognitive distraction were more pronounced than during CPM (p = 0.001).ConclusionsCPM and cognitive distraction reduced the PCES-induced pain to a similar extent. The more pronounced decrease of PCES-EP amplitudes after distraction by a cognitive task implies that both conditions might not represent the general pain modulatory capacity of individuals, but may underlie different neuronal mechanisms with the final common pathway of perceived pain reduction.
Highlights
Conditioned pain modulation (CPM) evaluates the effect of a painful conditioning stimulus (CS) on a painful test stimulus (TS)
After excluding an influence of the group affiliation during randomization on both pain intensity and amplitudes of painful cutaneous electrical stimulation (PCES)-evoked potentials data from both groups were pooled for all analyses
In summary, using the recently introduced novel CPMparadigm we demonstrated that both PCES-induced pain and PCES-Evoked potentials (EP) amplitudes can be reduced by CPM [20, 39] and during distraction by a cognitive task
Summary
Conditioned pain modulation (CPM) evaluates the effect of a painful conditioning stimulus (CS) on a painful test stimulus (TS). We aimed to compare the effect of CPM with cognitive distraction on PCES-induced pain and PCES-EP amplitudes. CPM has been extensively studied both in animals [16, 17] and humans using psychophysiological and electrophysiological methods [18,19,20,21,22,23,24], it is still under debate whether the pain reduction during CS results solely from the descending noxious inhibitory pathways. Pain modulation can be achieved by cognitive factors like attention and distraction [25,26,27]. Subjects’ attention has to be actively directed elsewhere to avoid that painful stimuli prevail over competing non-painful ones [34,35,36,37]. Interestingly, both CS and distraction by a cognitive visual task reduced pain intensity of heat stimuli in an additive manner [38]
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