Daydream believer: Rats dream of a better future

Researchers hope research into rodents' sleep will provide insight into what goes on in the human mind during sleep.

It seems humans are not alone when it comes to dreaming of a better life for themselves: apparently, rats do it, too. 

When at rest, rats and mice conduct mental rehearsals of journeys toward a desired future, such as a tasty treat, researchers at University College London (UCL) have found. The new study, which compared rats’ brain activity while the animals were in various stages of motion and rest, could help explain why some people with damage to the hippocampus – the part of the brain thought to be responsible for memory and spatial recognition – struggle to imagine the future.

It could also provide insight into what goes on in the human mind during sleep.

“During exploration, mammals rapidly form a map of the environment in their hippocampus,” Dr. Hugo Spiers, the study’s senior author, told research news site Science Daily. “During sleep or rest, the hippocampus replays journeys through this map which may help strengthen the memory.”

The researchers used electrodes to monitor the animals’ brain activity in three different situations: first, as the rats were shown food they couldn’t access, then as they rested in a separate area, and lastly, as they walked to the food. They found that brain cells involved in navigation showed similar activity when the rats were resting and when they were walking to and from the food, indicating that the brain was simulating or preparing future paths leading to a desired goal.

The process took up about 8 percent of the rats’ brain activity during sleep. While that may not sound like much, it’s still a lot of energy to give a single task during rest, Dr. Spiers told Discover magazine.

The results support the idea that sleeping improves performance on certain memory tasks, particularly those tied to a specific desire, the magazine reported.

“People are much better at doing the stuff that they’ll make more money on after they’ve slept,” Spiers said. “Something about sleep is using that desire information: that you do want to do better.”

The study stopped short of conclusively finding that rats dream these mental replays – “You can’t ask rats what they’re thinking or dreaming,” Spiers told Discover – but it does suggest that the ability to imagine future events is not unique to humans.

“What's really interesting is that the hippocampus is normally thought of as being important for memory, with place cells storing details about locations you’ve visited,” the study’s co-lead author, Dr. Freyja Ólafsdóttir, told Science Daily. “What’s surprising here is that we see the hippocampus planning for the future, actually rehearsing totally novel journeys that the animals need to take in order to reach the food.”