How much do you know about that three-pound hunk of tissue in your head - your brain? Its structure and function drive your behavior in profound ways. Scientists are studying the brain and its chemicals to find behavioral patterns, to figure out the sources of good moods and random outbursts, for example. This compilation from Science News for Students turns to brain science to answer all sorts of questions: Can you actually be addicted to your phone? Why is it so hard to sleep away from home? And does school really need to start so early?