Department of Psychology, York University, Toronto, ON, Canada;
J Pain Res. 2011 Mar 15;4:67-77. doi: 10.2147/JPR.S15966.
The present study examined whether 1) placebo hypoalgesia can be generated through implicit associative learning (ie, conditioning in the absence of conscious awareness) and 2) the magnitude of placebo hypoalgesia changes when expectations about pain are made explicit. The temperature of heat pain stimuli was surreptitiously lowered during conditioning trials for the placebo cream and the magnitude of the placebo effect was assessed during a subsequent set of trials when the temperature was the same for both placebo and control conditions. To assess whether placebo hypoalgesia could be generated from an implicit tactile stimulus, a 2 × 2 design was used with direction of cream application as one factor and verbal information about which cream was being applied as the second factor. A significant placebo effect was observed when participants received verbal information about which cream was being applied but not following implicit conditioning alone. However, 87.5% of those who showed a placebo response as the result of implicit conditioning were able to accurately guess the order of cream application during the final trial, despite a lack of awareness about the sensory manipulation and low confidence in their ratings, suggesting implicit learning in some participants. In summary, implicit associative learning was evident in some participants but it was not sufficient to produce a placebo effect suggesting some level of explicit expectation or cognitive mediation may be necessary. Notably, the placebo response was abolished when expectations were made explicit, suggesting a delicate interplay between attention and expectation.
1）在缺乏意识觉察的情况下，是否可以通过内隐联想学习（即条件反射）产生安慰剂镇痛作用；2）当明确表达对疼痛的预期时，安慰剂镇痛作用的程度是否会发生变化。在安慰剂乳膏的条件反射试验期间，隐秘地降低了热痛刺激的温度，在随后的一组试验中，当安慰剂和对照条件下的温度相同时，评估了安慰剂效应的幅度。为了评估安慰剂镇痛作用是否可以由内隐触觉刺激产生，采用了 2×2 设计，乳膏应用的方向是一个因素，关于应用哪种乳膏的口头信息是第二个因素。当参与者接收到关于应用哪种乳膏的口头信息时，观察到了显著的安慰剂效应，但在单独进行内隐条件反射时则没有。然而，在最后一次试验中，尽管参与者对感觉处理缺乏意识，对自己的评价缺乏信心，但有 87.5%的人能够准确猜测乳膏的应用顺序，这表明一些参与者存在内隐学习。总之，一些参与者表现出内隐联想学习，但不足以产生安慰剂效应，这表明可能需要一定程度的明确预期或认知调节。值得注意的是，当明确表达预期时，安慰剂反应被消除，这表明注意力和预期之间存在微妙的相互作用。
