Dopamine is a neurotransmitter in the brain.
One of the interesting functions of dopamine is that it plays a very important role in reward-motivated behavior. In other words, it is the brain's way of rewarding us with a happy feeling. This can be a very powerful thing, because it can get us "hooked" on things--from playing video games to reading books. What gives you the extra mental boost? It's up to you to channel that motivation, so spend your time wisely!