Scientists haven't figured out exactly why some people struggle to focus or to stay still more than others. Many things, like the genes we got from our parents or the environment we grew up in, make us each unique and cause us to behave differently. While our brains are all built the same way, each person's brain works a little bit different. Some scientists think that the way chemical messages are sent in some parts of the brain makes it harder for some people to focus or wait, like children and adults with ADHD. They don't mean to bother their friends or make their teachers or parents mad by not focusing or waiting, but it is just so much harder for them.
Scientists think that several parts of the brain may be associated with the symptoms of ADHD. Right in the center of the brain, there is a part called the striatum—say it like "strai-ay-tuhm." This part of the brain becomes more active in response to experiences that are fun, tasty, or new. The striatum is made up of many neurons—neurons are nerve cells with the special function of carrying messages throughout our brain and body.

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