A stimulator is something that makes a person or an animal more active or more interested in something.
A stimulator can be something that makes you feel excited or happy.
Examples:
The video game is a stimulator for my brain.
The music is a good stimulator for dancing.
The toy is a stimulator for the baby.
The new book is a good stimulator for my imagination.
The roller coaster is a big stimulator for fun.
The movie is a big stimulator for my feelings.