Social contact can transfer the feeling of pain or fear in several animal species, including humans, but the exact neural mechanisms for this transmission are still being studied. Now, Monique Smith and colleagues demonstrate that the social transmission of pain and pain relief in mice is mediated by neural projections from the brain's anterior cingulate cortex (ACC) to the nucleus accumbens. The transfer of fear, however, is mediated by the ACC's projections into a different area of the brain called the basolateral amygdala. The findings help untangle the distinct neural circuits involved in empathy, which in its simplest form is the ability to "feel" the affective states of others, say the researchers. A better understanding of how empathy is created in the brain "...may teach us about what goes wrong when empathy becomes maladaptive or is hampered as is the case in several psychiatric diseases," Alexandra Klein and Nadine Gogolla note in a related Perspective. In several experiments with mice, Smith et al. show how pain and fear can be socially transferred between affected and "bystander" mice, using a mix of visual, olfactory, and auditory cues. Using optogenetic methods, among others, they traced neuronal activity in the bystander mice to pinpoint exactly how the ACC induces this effect in the brain. The study also demonstrates for the first time that pain relief via an analgesic drug can be transferred socially, possibly offering an interesting model for socially-induced pain relief among humans, the researchers note.
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Journal
Science