Abstract:

Pain and reward are two basic motivational factors that regulate human perception and behavior, and can provide individuals with different behavioral motivations and subjective value experiences. Both pain avoidance sand reward seeking are essential for survival. Pain can be categorized into acute and chronic pain, and reward can be differentiated into a motivational component in the anticipatory phase and a hedonic component in the experiential phase. Acute pain increases the motivational component of reward and increases or decreases the hedonic component of reward, whereas chronic pain decreases the motivational component of reward and, and generally, decreases the hedonic component of reward.The neural mechanisms by which pain affects reward are mainly related to changes in the dopamine and opioid systems and neural activity in the medial prefrontal cortex(mPFC). Acute pain affects reward processing through neural mechanisms related to increased dopamine release, functional changes in the opioid system, and modulation of the mPFC. On the other hand, chronic pain leads to abnormal changes in the dopamine system, opioid system, and functional connectivity of the mPFC -voxel nucleus in the reward circuit, and reduces activation of brain regions associated with reward processing. These changes in neural mechanisms suggest that adaptive changes in reward circuits based on pain experience can predict the chronicity of pain. Further analysis revealed that the different effects of acute and chronic pain on reward processing are due to the following four factors: First, different symptom expressions in acute and chronic pain; second, different activities of the dopamine and opioid systems in acute and chronic pain; third, different mechanisms of neural activity in the neural in acute and chronic pain; and fourth, different mechanisms of reward processing in acute and chronic pain caused. In acute pain conditions, activation of brain regions that overlap with reward circuits is enhanced, thereby enhancing the motivational and hedonic components of reward processing; in chronic pain conditions, activation of these brain regions is abnormal, reducing the motivational and hedonic components of reward processing. Owing to the inconsistencies between current findings and previous studies, many issues should be addressed and resolved in the future: First, the issue of reproducibility of studies and comparability of results must/should be addressed by standardizing the relevant experimental operations and using uniform experimental paradigms and measures. Second, the immediate neural activity changes in the neural corresponding with the effects of acute pain and chronic pain on reward processing can be further explored. Next, the differences between acute pain and chronic pain can be examined, and based on these differences, the question of whether different types of chronic pain have different effects on reward processing and different changes in reward processing circuits can be investigated, the effects of different types of chronic pain on reward processing neural circuits can be measured separately, and the transition from acute pain to chronic pain can be prevented. Finally, the effects of different types of chronic pain on reward processing can be explored based on the co-morbidity of chronic pain and mood disorders, and further, the effects of different types of chronic pain on reward processing can be explored. Based on this, the relationship between different degrees of deficits, different types of chronic pain, and mood disorders should be clarified.

Key words: pain, acute pain, chronic pain, reward, motivational component, hedonic component