預期疼痛下的神經機轉

Abstract

疼痛是一種容易受到許多認知功能而影響的負面經驗。其中，對於將要接受的疼痛刺激的不同程度的預期也大大的影響我們對於痛覺的主觀感受。雖然已有先前研究對於預期疼痛的神經機轉，然而在增加疼痛的預期以及減少疼痛的預期的關係仍然不清楚，並且目前仍然沒有研究顯示不確定性對於疼痛預期所扮演的角色。為了釐清這些議題，我們招募健康成年人在不同預期的情況下接受功能性磁振造影掃描。首先我們假設增加疼痛的預期和減少疼痛的預期涉及不同的腦區，另外我們也推測不確定疼痛強度的預期和確定疼痛強度的預期由相異的腦區參與。行為結果顯示不確定的預期會增加疼痛評分。功能性磁振造影的分析更進一步顯示說在仍未接受刺激的預期階段，不確定預期和預期強烈疼痛刺激的全腦活動模式相似。另外當受試者在接受疼痛刺激時，我們發現不論何種預期的種類，都有喙部的前扣帶迴皮質和前腦島皮質作為共同的活化區域。這些結果證明了在行為和神經層級上預期對於疼痛的影響，也提供了在不同種類的疼痛預期影響下的相異和共享之神經機制的證據。

Human experiences of pain are robustly shaped by the anticipation of incoming noxious stimuli. Although prior research has explored the neural substrates underlying the anticipation of pain, whether anticipation of increased pain engages similar brain activity as the anticipation of decreased pain remains elusive, and no study so far has examined the role of uncertainty in pain anticipation. To address these issues, we recruited healthy adults to receive fMRI scanning under different anticipation conditions. We hypothesized that anticipation of increased and decreased pain engaged distinct brain regions. We also speculated that anticipation of uncertain pain intensity involved dissimilar brain areas from those related to the anticipation of certain pain intensity. Behavioral results showed that uncertain anticipation enhanced pain ratings. Our fMRI analyses further revealed that, during the anticipation phase, the whole-brain activation patterns in uncertain anticipation and the anticipation of an incoming high pain stimulus were similar. When participants received painful stimuli, we found that, irrespective of the type of anticipation, the rostral portion of the anterior cingulate cortex and the anterior insular cortex were commonly activated regions. These results demonstrate how anticipation affects pain at behavioral and neural levels and provide evidence that distinct and shared neural mechanisms underlie the influence of different types of anticipation on pain experiences.