72 mice were split into 3 groups.
They all were to complete a maze 3 times over the course of a single week. While not attempting to solve the maze, they were forced to listen to nothing but music for 10 hours a day (or nothing).
One group listened to nothing but heavy metal for 10 hours a day.
The other listened to nothing but Mozart and other classical music for 10 hours a day.
The last had no music being played to them.
The mice that had no music managed to cut back their maze completion time by 5 minutes by the third trial.
The mice that listened to classical music managed to cut back their maze completion time by 8 and a half minutes by the third trial.
The mice that listened to Heavy Metal, however, ADDED 20 minutes to their maze completion time, and could not complete the full experiment because they all ended up killing each other.
Interesting, no?