The brain is much more active at night than during the day. Logically, you would think that all the moving around, complicated calculations and tasks and general interaction we do on a daily basis during our working hours would take a lot more brain power than, say, lying in bed. Turns out, the opposite is true. When you ... your brain turns on. Scientists don't yet know why this is but you can thank the hard work of your brain while you sleep for all those pleasant dreams.