Do Rats ‘Dream’ of Food? New Research Indicates They Just Might

New research out of University College London shows that rats may preplan while resting, which means that the ability to imagine future events may not be restricted to humans.

The scientists monitored the brain activity in rats during three phases: first, as the animals viewed food through a transparent corridor where the food was kept out of reach; then as the rats rested in a nearby chamber; and finally as the rats were released into the corridor and permitted to approach the food. And what the brain monitoring showed was that specialized cells, known as place cells, were activated in the same patterns while the rats rested as they were when the rats were travelling to and from the food.

"During exploration, mammals rapidly form a map of the environment in their hippocampus," says senior author Dr. Hugo Spiers (UCL Experimental Psychology) in a UCL press release. "During sleep or rest, the hippocampus replays journeys through this map which may help strengthen the memory. It has been speculated that such replay might form the content of dreams. Whether or not rats experience this brain activity as dreams is still unclear, as we would need to ask them to be sure! Our new results show that during rest the hippocampus also constructs fragments of a future yet to happen. Because the rat and human hippocampus are similar, this may explain why patients with damage to their hippocampus struggle to imagine future events."

The small corridor used in the experiment contained a T-junction at the end. Food was located at one end of the T arm; the other arm was empty. The rat could visualize the entire setup through transparent glass. The rat was given a good look at the setup, then removed to a separate location to rest. He was then placed back in the corridor and allowed to approach the food.

The brain monitoring showed that the rat's place cells, which would be used to provide an internal map of the corridor leading to food, were active while the rat rested. Cells that would lead the rat to the empty arm of the T were not activated during rest, indicating the rat's brain was working out a future path to the food.

"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," explains co-lead author Dr. Freyja ólafsdóttir (UCL Biosciences). "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."

More research is needed to clarify exactly what the rat's brain activity patterns mean, but they believe their study helps elucidate the role the hippocampus plays in preplanning. It also provides insight into animal behavior, since until now, preplanning was believed to be restricted to humans.

"What we don't know at the moment is what these neural simulations are actually for," says co-lead author Dr. Caswell Barry (UCL Biosciences). "It seems possible this process is a way of evaluating the available options to determine which is the most likely to end in reward, thinking it through if you like. We don't know that for sure though and something we'd like to do in the future is try to establish a link between this apparent planning and what the animals do next."