Atlas Lauren Y, Wager Tor D
National Center for Complementary and Alternative Medicine, National Institutes of Health, 10 Center Drive, Rm 4-1741, Bethesda, MD, 20892, USA,
Handb Exp Pharmacol. 2014;225:37-69. doi: 10.1007/978-3-662-44519-8_3.
Placebo treatments reliably reduce pain in the clinic and in the lab. Because pain is a subjective experience, it has been difficult to determine whether placebo analgesia is clinically relevant. Neuroimaging studies of placebo analgesia provide objective evidence of placebo-induced changes in brain processing and allow researchers to isolate the mechanisms underlying placebo-based pain reduction. We conducted formal meta-analyses of 25 neuroimaging studies of placebo analgesia and expectancy-based pain modulation. Results revealed that placebo effects and expectations for reduced pain elicit reliable reductions in activation during noxious stimulation in regions often associated with pain processing, including the dorsal anterior cingulate, thalamus, and insula. In addition, we observed consistent reductions during painful stimulation in the amygdala and striatum, regions implicated widely in studies of affect and valuation. This suggests that placebo effects are strongest on brain regions traditionally associated with not only pain, but also emotion and value more generally. Other brain regions showed reliable increases in activation with expectations for reduced pain. These included the prefrontal cortex (including dorsolateral, ventromedial, and orbitofrontal cortices), the midbrain surrounding the periaqueductal gray, and the rostral anterior cingulate. We discuss implications of these findings as well as how future studies can expand our understanding of the precise functional contributions of the brain systems identified here.
安慰剂治疗在临床和实验室中都能可靠地减轻疼痛。由于疼痛是一种主观体验，因此很难确定安慰剂镇痛是否具有临床相关性。安慰剂镇痛的神经影像学研究提供了安慰剂诱导大脑处理过程变化的客观证据，并使研究人员能够分离出基于安慰剂的疼痛减轻背后的机制。我们对25项安慰剂镇痛和基于预期的疼痛调节的神经影像学研究进行了正式的荟萃分析。结果显示，安慰剂效应和对减轻疼痛的预期会使在通常与疼痛处理相关的区域（包括背侧前扣带回、丘脑和岛叶）进行有害刺激时的激活可靠地减少。此外，我们观察到在杏仁核和纹状体进行疼痛刺激时，激活持续减少，这两个区域在情感和评估研究中广泛涉及。这表明安慰剂效应在传统上不仅与疼痛相关，而且更普遍地与情感和价值相关的大脑区域上最为强烈。其他大脑区域在预期减轻疼痛时显示出激活可靠增加。这些区域包括前额叶皮质（包括背外侧、腹内侧和眶额叶皮质）、围绕导水管周围灰质的中脑以及喙部前扣带回。我们讨论了这些发现的意义以及未来研究如何能够扩展我们对这里确定的大脑系统精确功能贡献的理解。
