Share 'What Caffeine Actually Does to Your Brain'

For all of its wild popularity, caffeine is one seriously misunderstood substance. It's not a simple upper, and it works differently on different people with different tolerances—even in different menstrual cycles. But you can make it work better for you. Photo by rbrwr. We've covered all kinds of caffeine "hacks" here at Lifehacker, from taking "caffeine naps" to getting "optimally wired." And,…