Reicherts Philipp, Pauli Paul, Mösler Camilla, Wieser Matthias J
Department of Psychology, University of Würzburg, Würzburg, Germany.
Center of Mental Health, University of Würzburg, Würzburg, Germany.
Front Psychiatry. 2019 Sep 24;10:663. doi: 10.3389/fpsyt.2019.00663. eCollection 2019.
According to the motivational priming hypothesis, unpleasant stimuli activate the motivational defense system, which in turn promotes congruent affective states such as negative emotions and pain. The question arises to what degree this bottom-up impact of emotions on pain is susceptible to a manipulation of top-down-driven expectations. To this end, we investigated whether verbal instructions implying pain potentiation vs. reduction (placebo or nocebo expectations)-later on confirmed by corresponding experiences (placebo or nocebo conditioning)-might alter behavioral and neurophysiological correlates of pain modulation by unpleasant pictures. We compared two groups, which underwent three experimental phases: first, participants were either instructed that watching unpleasant affective pictures would increase pain (nocebo group) or that watching unpleasant pictures would decrease pain (placebo group) relative to neutral pictures. During the following placebo/nocebo-conditioning phase, pictures were presented together with electrical pain stimuli of different intensities, reinforcing the instructions. In the subsequent test phase, all pictures were presented again combined with identical pain stimuli. Electroencephalogram was recorded in order to analyze neurophysiological responses of pain (somatosensory evoked potential) and picture processing [visually evoked late positive potential (LPP)], in addition to pain ratings. In the test phase, ratings of pain stimuli administered while watching unpleasant relative to neutral pictures were significantly higher in the nocebo group, thus confirming the motivational priming effect for pain perception. In the placebo group, this effect was reversed such that unpleasant compared with neutral pictures led to significantly lower pain ratings. Similarly, somatosensory evoked potentials were decreased during unpleasant compared with neutral pictures, in the placebo group only. LPPs of the placebo group failed to discriminate between unpleasant and neutral pictures, while the LPPs of the nocebo group showed a clear differentiation. We conclude that the placebo manipulation already affected the processing of the emotional stimuli and, in consequence, the processing of the pain stimuli. In summary, the study revealed that the modulation of pain by emotions, albeit a reliable and well-established finding, is further tuned by reinforced expectations-known to induce placebo/nocebo effects-which should be addressed in future research and considered in clinical applications.
根据动机启动假说，不愉快的刺激会激活动机防御系统，进而促进诸如负面情绪和疼痛等一致的情感状态。由此产生的问题是，这种自下而上的情绪对疼痛的影响在多大程度上容易受到自上而下驱动的期望的操纵。为此，我们研究了暗示疼痛增强与减轻的言语指令（安慰剂或反安慰剂期望）——随后通过相应的体验（安慰剂或反安慰剂条件作用）得到证实——是否可能改变不愉快图片对疼痛调节的行为和神经生理相关性。我们比较了两组，这两组经历了三个实验阶段：首先，参与者要么被指示观看不愉快的情感图片会增加疼痛（反安慰剂组），要么观看不愉快的图片会比中性图片减轻疼痛（安慰剂组）。在随后的安慰剂/反安慰剂条件作用阶段，图片与不同强度的电疼痛刺激一起呈现，强化这些指令。在随后的测试阶段，所有图片再次与相同的疼痛刺激一起呈现。记录脑电图以分析疼痛的神经生理反应（体感诱发电位）和图片处理[视觉诱发电位晚期正电位（LPP）]，此外还进行疼痛评分。在测试阶段，反安慰剂组中观看不愉快图片时给予的疼痛刺激评分相对于中性图片显著更高，从而证实了疼痛感知的动机启动效应。在安慰剂组中，这种效应相反，即与中性图片相比，不愉快图片导致疼痛评分显著更低。同样，仅在安慰剂组中，与中性图片相比，不愉快图片期间体感诱发电位降低。安慰剂组的LPP未能区分不愉快图片和中性图片，而反安慰剂组的LPP显示出明显的差异。我们得出结论，安慰剂操纵已经影响了情绪刺激的处理，进而影响了疼痛刺激的处理。总之，该研究表明，尽管情绪对疼痛的调节是一个可靠且已确立的发现，但通过强化期望（已知会诱发安慰剂/反安慰剂效应）会进一步调节这种调节，这一点应在未来研究中加以探讨并在临床应用中予以考虑。
