The question of whether dreams actually have a physiological, biological or psychological function has yet to be answered. But that hasn't stopped scientists from researching and speculating. There are several theories as to why we dream. One is that dreams work hand in hand with sleep to help the brain sort through everything it collects during the waking hours. Your brain is met with hundreds of thousands, if not millions of inputs each day. Some are minor sensory details like the color of a passing car, while others are far more complex, like the big presentation you're putting together for your job. During sleep, the brain works to plow through all of this information to decide what to hang on to and what to forget. Some researchers feel like dreams play a role in this process. But even with these discoveries, the question of why we dream remains unanswered. Some researchers think dreaming might have evolved for physiological reasons. There is a great deal of neuronal activity occurring while we sleep, especially in REM, and it has been suggested that dreams may just be a meaningless by-product of this biological function.