New research may have revealed what sleeping rats dream about.
A recent study found rats' brains simulate paths to their desired future, such as a tasty treat, University College London reported. To make their findings, a team of researchers monitored brain activity in rats as they were shown food but could not reach it, as they took a nap, and when they were finally allowed to reach the treat. They found specialized brain cells simulated a path to the food as the rats rested.
"During exploration, mammals rapidly form a map of the environment in their hippocampus," said senior author Hugo Spiers of UCL Experimental Psychology. "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."
During the rest period, the cells that would later provide an internal map to the food were observed to be active.
"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 Freyja Ólafsdóttir of 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."
The finding suggest the hippocampus is responsible for planning routes, even ones that have not yet been taken, when there is a stimulus such as food involved. The findings also imply dreaming and imagining future events is a not a trait that is uniquely human.
"What we don't know at the moment is what these neural simulations are actually for," said co-lead author Caswell Barry of 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."
The findings were published in a recent edition of the journal eLife.
