Abstract
Objective: Pain and affective disorders have clear clinical relevance; however, very few studies have investigated the association between pain and bipolar disorder. This study investigated the brain activity of patients with bipolar disorder (BPs) undergoing tonic pain and assessed the interaction between pain and emotion.Methods: Ten BPs and ten healthy controls (HCs) were exposed to emotional pictures (positive, neutral, or negative), tonic pain only (pain session), and emotional pictures along with tonic pain (combined session). A moderate tonic pain was induced by the infusion of hypertonic saline (5% NaCl) into the right masseter muscle with a computer-controlled system. Whole-brain blood oxygenation level dependent (BOLD) signals were acquired using 3T functional resonance imaging (fMRI).Results: Ten BPs and ten healthy participants were included in the final analysis. During the pain session, BPs accepted more saline, but showed lower pain rating scores than HCs. When experiencing pain, BPs showed a significant decrease in the BOLD signal in the bilateral insula, left inferior frontal gyrus (IFG), and left cerebellum as compared with HCs. In the combined session, the activated regions for positive mood (pain with positive mood > baseline) in BPs were the left cerebellum, right temporal gyrus, and left occipital gyrus; the activated regions for negative mood (pain with negative mood > baseline) were the right occipital gyrus, left insula, left IFG, and bilateral precentral gyrus.Conclusions: This study presents the preliminary finding of the interaction between pain and emotion in BPs. BPs exhibited lower sensitivity to pain, and the activation of insula and IFG may reflect the interaction between emotion and pain stimulus.
Highlights
The prevalence of pain interference is elevated in patients with bipolar disorder (BPs) [1]
The results show that BPs accepted more saline during pain session (PS), whereas their average visual analog scale (VAS) score was lower than that of healthy controls (HCs)
This study presents the preliminary finding of the interaction between pain and emotion in BPs, both increased activation in response to emotional stimuli and decreased activation in response to painful stimuli were observed in BPs
Summary
The prevalence of pain interference is elevated in patients with bipolar disorder (BPs) [1]. Compared with the general population, BPs are at significantly increased risk of clinically relevant pain [Relative Risk (RR) = 2.14] [2]. Patients with affective disorders reportedly have abnormal pain perception [3]. Pain and emotion are linked in many ways [7, 8]; mood and emotional state alter pain perception both in healthy persons and in patients with affective disorders [9]. In the experimental context, creating a positive emotional state, such as by seeing pleasant pictures or watching humorous films, generally reduces pain sensitivity. A negative emotional state increases pain sensitivity, these effects are less reliable than those related to positive state. The insula is the key area for pain perception and evaluation [13], and the interaction of emotion and pain activates the insula and secondary somatosensory cortex [7]
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