Researchers have created a brain implant that stimulates persistent aggression. Winners in social dominance experiments are mice that are not stronger but are just more persistently aggressive.
The brain circuits of a winner
Social dominance in mice depends on their history of winning in social contests. Zhou et al. found that this effect is mediated by neuronal projections from the thalamus to a brain region called the dorsomedial prefrontal cortex. Selective manipulation of synapses driven by this input revealed a causal relationship between circuit activity and mental effort–based dominance behavior. Thus, synapses in this pathway store the memory of previous winning or losing history.
Mental strength and history of winning play an important role in the determination of social dominance. However, the neural circuits mediating these intrinsic and extrinsic factors have remained unclear. Working in mice, we identified a dorsomedial prefrontal cortex (dmPFC) neural population showing “effort”-related firing during moment-to-moment competition in the dominance tube test. Activation or inhibition of the dmPFC induces instant winning or losing, respectively. In vivo optogenetic-based long-term potentiation and depression experiments establish that the mediodorsal thalamic input to the dmPFC mediates long-lasting changes in the social dominance status that are affected by history of winning. The same neural circuit also underlies transfer of dominance between different social contests. These results provide a framework for understanding the circuit basis of adaptive and pathological social behaviors.
Neuroscientist Zhou Tingting of the Chinese Academy of Sciences, Shanghai, joined with his colleagues to measure mouse social dominance using what’s called the “tube test.” The tube test creates a scenario in which there’s not enough room for the mice to pass each other in the tube. Mice have to shove one another aside to get out. The mouse who shoves the most other mice out of its way will “win” the dominance game.
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