8 Things Scientists Still Don't Understand About Your Brain

6. Why Do We Sleep And Dream?

Sleep is obviously extremely important. Despite the risks and drawbacks of spending a large proportion of your day, and as much as a third of your life, unconscious, unaware and defenceless, all mammals, reptiles and birds sleep. It's clearly vital, but we have no idea why.

For a start, there's no real reason why sleep should give you energy. We get our energy by converting it from food, and yet there's no way you could eat your way out of needing sleep. You actually burn through a lot of energy as you sleep, and yet that you wake up feeling refreshed and more energetic than when you went to bed is something that still baffles scientists.

The same goes for dreaming. There are plenty of guesses, from random neural firing to memory consolidation to deep learning, but as far as science is concerned, dreaming is as much of a mystery as it has been for thousands of years.