In the 1960s, the University of California at Berkeley conducted a series of experiments on the cognitive ability of mice. In the experiment, one group of mice were placed in a cage filled with various toys, wheels and tunnels, while the other group grew up in an empty cage. The experimental results showed that the brain of the former group was larger, cognitive ability is also significantly higher than the latter group. 
Before the experiment, there was little individual difference between the two groups.
 the researchers infer that sufficient external stimulation can change the structure and ability of the brain.