VICARIOUS PAIN INCREASES DOPAMINE RELEASE IN MICE

The ability to recognize the emotional states of others and modify one's own behavior forms the foundation of sociality. Recognizing negative emotions, such as another's suffering, is particularly involved in complex social emotions like negative empathy and Schadenfreude, making the elucidation of its neural basis crucial. The dopamine system in the nucleus accumbens (NAc), central to reward and motivation, has been implicated in these social emotions (Takahashi et al., Science, 2009). However, much remained unknown about dopamine dynamics in the NAc during real-time observation of another's pain, particularly its habituation properties and upstream control circuits. We investigated NAc dopamine dynamics in mice observing another mouse's pain using fiber photometry. We found a significant increase in dopamine within the observing mouse's NAc immediately after the other mouse experienced pain. To verify the specificity of this response, we compared it to the response to a non-social, negative auditory stimulus. Although dopamine in the NAc also increased in response to the auditory stimulus, this response significantly decreased over sessions, indicating habituation. In contrast, the dopamine increase following observation of another individual's pain showed no significant decrease over sessions, suggesting a persistent response resistant to habituation. These results suggest that the social stimulus of observing another's pain undergoes distinct neural processing compared to the non-social auditory stimulus and repeatedly activates the NAc dopamine system. This study provides new evidence that social information about others' pain drives a response in the NAc dopamine system that is resistant to habituation.