Classically conditioned modulation of pain depends on stimulus intensity

Abstract

Innocuous cues that become associated with pain can enhance pain. This is termed classically conditioned hyperalgesia. The size of this effect varies under different conditions. We aimed to test whether the sensitising effect of pain-associated cues depends on the intensity of the paired test stimulus. To do this, two virtual reality environments were paired with either painful or non-painful vibrotactile stimuli in a counterbalanced fashion. The differential effect of the two environments was evaluated using pain intensity ratings of paired electrocutaneous test stimuli at three different intensity levels. Forty healthy participants were included in the study; 30 participants experienced sufficient pain during the learning phase and were included in the main analysis. An effect of environment (p = 0.014) and interaction between environment and test stimulus intensity was found (p = 0.046). Only the most intense test stimulus was modulated by environment. While the effect was small, the results are consistent with the proposition that pain-associated cues may induce hyperalgesia to some degree, under certain conditions. In particular, results highlight the potential relevance of stimulus intensity during and after the initial painful experience. Further attention is needed to comprehensively understand the variables that impact classically conditioned hyperalgesia.

Keywords: Associative learning; Chronic pain; Classical conditioning; Conditioned hyperalgesia; Nocebo; Psychophysics.

Fig. 1

Stages of the experiment

Fig. 2

Overview of the study and analysis procedure

Fig. 3

The average percentage difference between CS + /US and CS–US pairings among participants. An asterisk is shown where a significant difference was found between pain- and vibration-associated environments