Researchers at the Massachusetts Institute of Technology say they have entered the dreams of rats and found them busily working their way through the same lab mazes they negotiate during the day.
It is evidence not just that animals dream - most pet owners know that already - but that they have complex dreams, replaying events much the way humans do, researchers said. And they may use their dreams to learn or memorize.
The findings, announced Wednesday, could eventually help researchers understand how the human mind works in the murky world of the subconscious.
"It's really opening a new door into the study of dreams," said Matt Wilson, associate professor at MIT's Center for Learning and Memory and leader of the study, published in Friday's issue of the journal Neuron.
But Robert Stickgold, assistant professor of psychiatry at Harvard Medical School, said there is no way to prove MIT researchers were seeing rats dream.
"If the rat would tell us, 'Yes, I was dreaming about running around the track,' then we'd have it nailed down," Stickgold said.
The rats in the MIT study were hooked up to a device that measured the pattern of neurons firing in the hippocampus, an area of the brain known to be involved in memory.
The scientists had the rats perform specific tasks in a maze that produced very distinctive patterns of brain activity. When they repeatedly saw almost exactly the same patterns reproduced during sleep, they concluded the rats were dreaming about running through the maze.
The correlation was so great that scientists said they could place where in the maze the rat was dreaming it was.
The discovery of similarities between human and animal dreams could enable scientists to use the rats to learn more about the human mind, Wilson said. Scientists could manipulate the rats' experiences in a way that is not permissible with people.
For instance, some scientists believe people solve problems in their dreams. The theory could be tested on rats, he said.
Scientists also believe that dreams help form and reinforce long-term memories. The MIT findings may bolster that theory.
Wilson's research was funded in part by the National Institutes of Health.