An experiment carried out this year showed that rats actually “dream” when faced with the prospect of future rewards! Researchers placed rats in a location where they could see food, but not reach it, then let them rest in a separate room, and finally allowed them to walk to the food and enjoy it at last. During each stage, they monitored the brain activity of the rats, and found that the parts of their brains involved in navigation were active not only during their travels to the food, but also while they were asleep in the separate room.
Now, it’s only a theory that this brain activity can be experienced by the rats as a dream, and it’s possible that it’s simply their brains reviewing and strengthening its view of the world. But I like to think that during rest they’re imagining a brighter future filled with all sorts of treats, because after all, I’m sure we’re all guilty of that!
More reading:
https://www.ucl.ac.uk/news/news-articles/0615/260615-rats-dream-paths-future
the Runaway Lab Book 