Most soda has caffeine in it. Caffeine tends to wake the body up, causing you to feel more alert, but with increased use your body builds up a tolerance to it. Drinking larger amounts of caffeine "can cause nervousness, sweating, tenseness, upset stomach, anxiety, and insomnia".
Soda also has a lot of sugar in it, which can make you hyperactive, and can cause some fuzzy thinking.
As with most things, having a single soda once in awhile wont kill you, but overindulging in it wont be good for a healthy mind or a healthy body.
Best of luck in researching sugar more. Here are a few links to help you out.