Egorova N, Park J, Kong J
Department of Psychiatry, Massachusetts General Hospital/Harvard Medical School, Charlestown, USA.
Eur J Pain. 2017 Aug;21(7):1243-1251. doi: 10.1002/ejp.1024. Epub 2017 May 12.
Visual cue conditioning is a valuable experimental paradigm to investigate placebo and nocebo effects in pain. However, little attention has been paid to the cues themselves and potential variability of effects (their quantity and quality) stemming from the choice of stimuli. Yet, this seemingly methodological question has important implications for the interpretation of experimental findings in terms of their significance for clinical practice.
We investigated the effect of heat pain conditioning using different types of visual cues (abstract images, faces and pseudo-words) in a group of 22 healthy volunteers. We analysed conditioning effects calculated as the difference in pain ratings to heat stimuli of identical temperature preceded by conditioned high or low pain cues with (1) subliminal and supraliminal presentation; and (2) immediately after conditioning and following extinction. Awareness manipulation and test following indirect, observational extinction allowed us to assess the strength and robustness of the conditioning effects induced with different cue types.
We observed no differences in conditioning effect magnitudes between images, faces and words when all stimuli were presented supraliminally. With subliminal presentation, only face stimuli elicited a significant effect; equally only face cue-induced effect withstood extinction.
Our findings indicate that face-related associations to pain might be stronger than those elicited with other visual cues, as face cues seem to induce stronger subliminal effects and withstand mild extinction.
We compared different types of neutral cues commonly used in conditioning paradigms and found that faces elicited a stronger, more robust nonconscious effect than abstract images or pseudo-words.
视觉线索条件反射是研究疼痛中安慰剂和反安慰剂效应的一种有价值的实验范式。然而，人们很少关注线索本身以及因刺激选择而产生的效应的潜在变异性（其数量和质量）。然而，这个看似方法学的问题对于根据实验结果对临床实践的意义来解释实验结果具有重要意义。
我们在22名健康志愿者中研究了使用不同类型的视觉线索（抽象图像、面部和伪词）进行热痛条件反射的效果。我们分析了条件反射效应，计算方法是将在呈现条件性高或低疼痛线索后对相同温度的热刺激的疼痛评分差异，其中包括（1）阈下和阈上呈现；以及（2）条件反射后立即和消退后。通过间接观察性消退后的意识操纵和测试，我们能够评估不同线索类型诱导的条件反射效应的强度和稳健性。
当所有刺激都阈上呈现时，我们观察到图像、面部和单词之间的条件反射效应大小没有差异。在阈下呈现时，只有面部刺激引发了显著效应；同样，只有面部线索诱导的效应在消退后仍然存在。
我们的研究结果表明，与疼痛相关的面部关联可能比其他视觉线索引发的关联更强，因为面部线索似乎能诱导更强的阈下效应并能抵抗轻度消退。
我们比较了条件反射范式中常用的不同类型的中性线索，发现面部比抽象图像或伪词引发更强、更稳健的非意识效应。
