Price D D, Milling L S, Kirsch I, Duff A, Montgomery G H, Nicholls S S
Departments of Oral and Maxillofacial Surgery and Neuroscience, University of Florida, P.O. Box 100416, Gainesville, FL 32610-0416, USA.
Pain. 1999 Nov;83(2):147-56. doi: 10.1016/s0304-3959(99)00081-0.
Placebo analgesia was produced by conditioning trials wherein heat induced experimental pain was surreptitiously reduced in order to test psychological factors of expectancy and desire for pain reduction as possible mediators of placebo analgesia. The magnitudes of placebo effects were assessed after these conditioning trials and during trials wherein stimulus intensities were reestablished to original baseline levels. In addition, analyses were made of the influence of these psychological factors on concurrently assessed pain and remembered pain intensities. Statistically reliable placebo effects on sensory and affective measures of pain were graded according to the extent of surreptitious lowering of stimulus strength during the manipulation trials, consistent with conditioning. However, all of these effects were strongly associated with expectancy but not desire for relief. These results show that although conditioning may be sufficient for placebo analgesia, it is likely to be mediated by expectancy. The results further demonstrated that placebo effects based on remembered pain were 3 to 4 times greater than those based on concurrently assessed placebo effects, primarily because baseline pain was remembered as being much more intense than it actually was. However, similar to concurrent placebo effects, remembered placebo effects were strongly associated with expected pain levels that occurred just after conditioning. Taken together, these results suggest that magnitudes of placebo effect are dependent on multiple factors, including conditioning, expectancy, and whether analgesia is assessed concurrently or retrospectively.
安慰剂镇痛是通过条件试验产生的，在这些试验中，热诱导的实验性疼痛被暗中减轻，以测试预期和减轻疼痛愿望等心理因素作为安慰剂镇痛可能的介导因素。在这些条件试验之后以及在刺激强度恢复到原始基线水平的试验期间，评估安慰剂效应的大小。此外，还分析了这些心理因素对同时评估的疼痛和记忆疼痛强度的影响。与条件作用一致，根据操作试验期间刺激强度暗中降低的程度，对疼痛的感觉和情感测量指标上具有统计学可靠性的安慰剂效应进行分级。然而，所有这些效应都与预期强烈相关，而与减轻疼痛的愿望无关。这些结果表明，虽然条件作用可能足以产生安慰剂镇痛，但它很可能是由预期介导的。结果还进一步表明，基于记忆疼痛的安慰剂效应比基于同时评估的安慰剂效应大3至4倍，主要是因为记忆中的基线疼痛比实际情况要强烈得多。然而，与同时出现的安慰剂效应类似，记忆中的安慰剂效应与条件作用后立即出现的预期疼痛水平密切相关。综上所述，这些结果表明安慰剂效应的大小取决于多种因素，包括条件作用、预期，以及镇痛是同时评估还是回顾性评估。
