社會等級在各種動物中十分常見，並且對維持社會結構有著重要的作用。由於年幼的動物不會表現出攻擊性行為，因此當前大多數對家鼠(Mus musculus)中的研究都集中在成年小鼠而非幼鼠的社會等級制度上。在本研究中，我們使用鑽管測試（一隻老鼠迫使其對手退縮離開管子）來建立幼鼠的社會等級制度，並檢查不同社會等級中幼鼠的行為表現。結果顯示幼鼠的社會等級與活動力、抑鬱和焦慮表現之間沒有顯著的相關性。意外的是從新物體識別測試和Y型迷宮的測驗結果顯示出，社會等級較高的小鼠表現出更好的記憶能力。另外qPCR的結果同樣表明，在社會階級較高的小鼠中，記憶相關基因的表達程度較高。最後，我們給小鼠注射了改善記憶的藥物，發現接受過藥物治療的小鼠不僅表現出更好的記憶力，同時表現出更高的社會階級，進一步支持了社會等級與記憶力之間的正關係。我們的研究通過採取行為測驗、分子和藥理學的方法，證明小鼠記憶力和社會等級之間的正相關。我們希望這個發現將為社交行為以及學習和記憶相關領域提供新的見解。

Social hierarchy is widespread in various animal species and plays an essential role in maintaining the social structure. In house mice, Mus musculus, since young animals do not perform aggressive behaviors, most current studies focus on the social hierarchy of adult but not young mice. Therefore, in this study, we used the tube test, one mouse forcing its opponent to back down from a tube was used to assess the social dominance of a mouse, to establish the first social hierarchy of weanling mice and examined a variety of behaviors across social ranks. Surprisingly, there is no significant correlation between the social ranks and mobility, depression-, and anxiety-like phenotypes in young mice. In contrast, the Novel Object Recognition Test and Y maze suggested that the weanling mice with higher social hierarchy showed better memory ability. The qPCR results also indicated higher expression of memory-related genes in mice with higher rank. Last, we injected memory-improving drugs into mice and found that mice treated with drugs showed not only better memory but also higher social dominance, further support the relationship between social hierarchy and memory. Together, by taking behavioral, molecular and pharmacological approach, our study reveals a positive correlation between memory and social hierarchy in mice. This finding may provide new insight into the fields of social interaction as well as learning and memory.
This study has been published in Communications Biology Chou, Y.J., Ma, Y.K., Lu, Y.H., King, J.T., Tasi, W.S., Yang, S.B., and Kuo, T.H. (2022). Potential cross-species correlations in social hierarchy and memory between mice and young children.

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