情緒在預期對痛覺調控中之角色

Abstract

對於疼痛的預期會強烈影響人類的痛覺感受，情緒則會潛在地干擾這個認知調控過程，然而，我們尚未了解正向情緒與負向情緒如何影響預期對疼痛的調控作用。在這個研究中，我們的目的在於釐清不同的情緒狀態是否會改變預期對痛覺經驗的調控效果，並且探討在不同情緒下預期調控痛覺的神經機轉。實驗過程中，我們透過呈現不同的視覺符號以操弄受試者對於痛覺強度之預期，同時，使用國際情緒圖片系統（International Affective Picture System）之圖片引起受試者正向、中性與負向情緒，於受試者接受電刺激產生痛覺感受時，透過功能性磁振造影技術（functional Magnetic Resonance Imaging），收集受試者之大腦神經反應，以研究情緒影響預期調控效果之腦神經機轉。行為結果上，在不同的情緒狀態中，我們都能觀察到預期對痛覺之調控效果，也就是即使受試者接受到的電刺激電流強度相同，當受試者預期一個較低強度之痛覺刺激時，受試者所報告的痛覺感受強度則顯著較低。更重要的是，相對於正向情緒，負向情緒明顯削弱了此預期效果。而在神經活動層次，不同的情緒狀態下，預期對疼痛的調控效果所伴隨的大腦活化區域並不相同，相較於正向情緒，負向情緒下的神經反應在前腦島皮質（anterior insular cortex）有較強的活化。這個研究增進了我們對於情緒和預期如何交互作用影響人類痛覺經驗的知識。

Expectations of pain significantly bias the experience of pain in humans. Different emotional valences potentially interfere this cognitive process. However, how pleasant and unpleasant emotions affect pain expectations remains unknown. In the present study, we aim to clarify whether different emotional states modulate effects of expectation on pain at the behavioral level and to investigate the underlying neural mechanisms. We manipulated participants’ expectation towards upcoming electrical painful stimuli by presenting different visual cues. Meanwhile, we induced pleasant, neutral, and unpleasant emotions by using the pictures selected from International Affective Picture System during the anticipation period of incoming painful stimulation. By using functional MRI, we examined brain activations related to painful stimuli to examine the neural substrates underlying the influence of emotions on the expectation of pain. Behaviorally, we observed a pervasive effect of expectation on pain across different emotional states. More importantly, expectation-related reduction in pain ratings during the unpleasant condition was significantly less than that under pleasant condition. At the neural level, brain activation patterns associated with pain modulation by expectations of decreased intensity differed among different emotional conditions, with the unpleasant condition associated with increased activations in the anterior insular cortex compared with the pleasant condition. The current research enhances our knowledge on how expectation interacts with emotion to shape human responses to pain.