Expectations underlie the effects of unpredictable pain: a behavioral and EEG study

Previous studies on potential effects of unpredictability on pain perception and its neural correlates yielded divergent results. This study examined whether this may be explained by expectations. We presented 41 healthy volunteers with laser heat stimuli of different intensities. The stimuli were preceded either by predictable low, medium or high cues or by unpredictable low-medium, medium-high or low-high cues. We recorded self-reports of pain intensity and unpleasantness and laser-evoked potentials (LEPs). Furthermore, we investigated whether dynamic expectations, i.e. evolving expectations based on actual pain experiences from preceding trials, were better predictors of pain ratings, as compared to fixed expectations based on the cued intensities. Our results replicate previous findings that unpredictable pain is higher than predictable pain for low-intensity stimuli, but lower for high-intensity stimuli. Furthermore, we observed higher ratings for the medium-high unpredictable condition as compared to the medium-low unpredictable condition, in line with an effect of expectations. We also observed that higher certainty of expectations strengthened the influence of expectations on pain intensity ratings. We found significant interactions (N1, N2) for the LEP components between intensity and predictability. However, the few significant differences in LEP peak amplitudes between cue conditions did not survive correction for multiple testing. In line with predictive coding perspectives, dynamic expectations better predicted pain perception than fixed expectations. Considering these findings, we highlight the importance of controlling for expectations and expectation certainty in pain unpredictability manipulations. We also suggest to conceptualize pain expectations more often as dynamic constructs adapting to previous experiences.