早期環境的不同，使鼠腦的發展及老腦的學習能力，有不同的表現。惟老鼠與環境間的關係，尚乏量化性的分析。本實驗將斷奶後之老鼠分成五組：變換玩具組，相同玩具組，變換玩伴組，相同玩伴組及控制組。分別觀察前四組老鼠與玩具（或玩伴老鼠）間的互動頻數，以期發現該互動頻數與腦重及學習的關係。結果發現變換玩具組之老鼠，有較高之互動頻數，但在腦重上，與其他組並無差異；在複Y迷津學習上，表現較佳。

　　　　　The favorable effect of an enriched environment on brain weight and learning in the rat has been reported. More specificaly, the social factor and toy factor of the environment have been investigated. However, direct quantitative measures of the interactions between rats, and between rat andtoy, are still lacking. The present study tries to probe the relation between these interactions and the brain weight or learning measures. Changing the rats' toys or rat-partnersis expected to increase the interaction frequency. 40 ratswere divided into five groups: same-toy, variable-toy, same partner, variable-partner and control-isolation groups. The results show lower interaction frequency in the same-toygroup. No brain weight difference was found among these five groups. The variable-toy group shows better performance than the other groups in. Multiple-Y-Maze learning.