Science has long wondered why we dream. From Freud's idea that dream fulfill our desires to the matter-of-fact notion that dreaming may be a side effect of REM (rapid-eye-movement) sleep, no theory has so far explained the mystery.

Harvard psychologist Deirdre Barrett has come to the conclusion that dreaming could be an effect of our capacity for critical thinking.

Her research revealed that our slumbering hours may help us solve puzzles that have plagued us during daylight hours. The visual and often illogical aspects of dreams make them perfect for the out-of-the-box thinking that is necessary to solve some problems, she speculates.

So while dreams may have originally evolved for another purpose, they have likely been refined over time for multiple tasks, including helping the brain reboot and helping us solve problems, she said.