Distraction by a cognitive task has a higher impact on electrophysiological measures compared with conditioned pain modulation

Background Conditioned 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. Methods PCES was performed in 38 healthy subjects using surface electrodes inducing a painful sensation of 60 (NRS 0-100) on one hand. In a crossover design subjects immersed the contralateral hand into painful cold water (10 °C, 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. Results Both CPM and cognitive distraction significantly reduced PCES-EP amplitudes (CPM: from 30.9 ± 9.9 µV to 24.35 ± 8.41 µV, cognitive distraction: from 33.0 ± 8.8 µV to 19.5 ± 6.5 µV, p < 0.05) and PCES-induced pain (CPM: from 58 ± 4 to 39 ± 12, cognitive distraction: from 58 ± 4 to 36 ± 14, p < 0.05), though the changes in pain intensity and PCES-amplitude did not correlate. The changes of the PCES-EP amplitudes during cognitive distraction were significantly more pronounced than during CPM. Conclusions The amount of pain relief induced by CPM and cognitive distraction seems to be similar. However, the even more pronounced decrease of PCES-EP amplitudes after distraction by a cognitive task implies that both conditions do not represent the general pain modulatory capacity of individuals, but may underlie different neuronal mechanisms with the final common pathway of perceived pain reduction.