Pain Research Group, Institute of Psychology, Jagiellonian University, Kraków, Poland.
Department of Kinesiotherapy and Special Methods in Physiotherapy, The Jerzy Kukuczka Academy of Physical Education, Katowice, Poland.
Eur J Pain. 2019 May;23(5):923-935. doi: 10.1002/ejp.1360. Epub 2019 Feb 1.
Placebo analgesia is explained by two learning processes: classical conditioning and observational learning. A third learning process, operant conditioning, has not previously been investigated as a mechanism of placebo effects. We aimed to induce placebo analgesia by operant conditioning.
Three groups of participants received electrocutaneous pain stimuli of the same intensity, preceded by either an orange or blue stimulus. In the conditioning phase of the study, participants from the experimental group were rewarded for low pain responses following one of the colour stimuli (placebo) and for high pain responses following the other colour stimuli (non-placebo). Moreover, they were punished when their pain responses were high following placebo stimuli and low following non-placebo stimuli. To investigate the role of contingency, that is dependent relation between rewards/punishers and pain responses, the random-control group received rewards and punishers in a non-contingent manner. The colour-control group did not receive any rewards or punishers to control for nonassociative learning. Pain intensity ratings were used as an outcome measure, and verbal feedback on pain ratings was used as rewards/punishers.
When rewarding and punishment were stopped, only participants from the experimental group experienced less pain following the placebo than following the non-placebo stimuli; that is, placebo analgesia was found in this group. This effect was not extinguished during the study.
Placebo analgesia can be induced by operant conditioning, which should be considered a third mechanism for producing placebo effects. Moreover, the contingency between pain responses and rewards/punishers is crucial to induce placebo analgesia through operant conditioning.
According to the current placebo literature, placebo analgesia can be explained by two learning processes: classical conditioning and observational learning. A third learning process, operant conditioning, has not previously been investigated as a mechanism of placebo effects. Our study reveals that patients can learn placebo analgesia as a result of operant conditioning, suggesting that randomized controlled trials could be improved by controlling the reinforcement that might occur spontaneously when patients interact with, for example, medical personnel.
安慰剂镇痛可以用两种学习过程来解释：经典条件作用和观察学习。第三种学习过程，操作性条件作用，以前尚未被研究为安慰剂效应的机制。我们旨在通过操作性条件作用诱导安慰剂镇痛。
三组参与者接受相同强度的电皮肤疼痛刺激，之前分别呈现橙色或蓝色刺激。在研究的条件作用阶段，实验组的参与者在以下两种颜色刺激中的一种（安慰剂）下，对低疼痛反应进行奖励，而在另一种颜色刺激（非安慰剂）下，对高疼痛反应进行奖励。此外，当他们的疼痛反应在安慰剂刺激下较高而在非安慰剂刺激下较低时，他们会受到惩罚。为了研究条件关系的作用，即奖励/惩罚与疼痛反应之间的依赖关系，随机对照组以非条件关系给予奖励和惩罚。颜色对照组不给予任何奖励或惩罚来控制非联想学习。疼痛强度评分被用作结果测量，而口头反馈的疼痛评分被用作奖励/惩罚。
当停止奖励和惩罚时，只有实验组的参与者在接受安慰剂后感到的疼痛比接受非安慰剂刺激时少；也就是说，在该组中发现了安慰剂镇痛。这种效果在研究过程中没有消失。
通过操作性条件作用，可以诱导安慰剂镇痛，这应被视为产生安慰剂效应的第三种机制。此外，疼痛反应和奖励/惩罚之间的条件关系对于通过操作性条件作用诱导安慰剂镇痛至关重要。
根据当前的安慰剂文献，安慰剂镇痛可以用两种学习过程来解释：经典条件作用和观察学习。第三种学习过程，操作性条件作用，以前尚未被研究为安慰剂效应的机制。我们的研究表明，患者可以通过操作性条件作用学习安慰剂镇痛，这表明随机对照试验可以通过控制患者与例如医务人员互动时可能自发发生的强化来得到改善。
