Study: Rats Dream About Running Mazes

B O S T O N, Jan. 24, 2001 -- Some rats apparently can't ever escape the rat race, even when they're sound asleep.

Researchers at the Massachusetts Institute of Technology say they've entered the dreams of rats and found them busily working their way through the same lab mazes they negotiated during the day. It's evidence not just that animals dream — most pet owners know that — 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 discovery, announced today, 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 lead researcher of the study, reported in Friday's issue of the journal Neuron. "It's not just a step forward, it's a step into a new domain."

Right Results, Wrong Specifics?

But Robert Stickgold, assistant professor of psychiatry at Harvard Medical School, said that while Wilson's research provides important evidence of sleep's role in memory, there's no way to prove MIT researchers were seeing rats dream. That's because the link between the rats' brain patterns and actual dreaming can't proved, he said. "He's got the right results, he's just got the wrong species," Stickgold said. "If the rat would tell us, 'Yes, I was dreaming about running around the track,' then we'd have it nailed down." "This is a good as it can get at this point," he added. The four-year study initially focused on memory, with researchers measuring brain activity of rats during various tasks. But after Wilson checked the rats' brain activity while sleeping, he found nearly identical brain patterns in dreaming and waking states. "At that point, it was kind of like a lightning bolt," he said.

Dreaming About the Rat Race?

For the next two years, researchers worked to prove the implications of the initial observation — that the rats were dreaming about their daily experiences. The rats 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 which produced very distinctive brain patterns. 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 — and even if it was dreaming of running or walking. The discovery of similarities between human and animal dreams enables scientists to use the rats to learn more about the human mind, Wilson said. Scientists can manipulate the rats' experiences in a way that's not permissible with people, and shed light on old theories, he said. For instance, some scientists believe people solve problems during sleep by synthesizing related experiences in a single dream, then learning from what the experiences have in common. The theory could be tested by exposing rats to multiple related experiences, he said.

Sleep’s Role in Memory

Scientists also believe that dreams help form and reinforce long-term memories. Stickgold said the fact the MIT rats were replaying memories in their minds — whether they were dreaming or not — proves how important sleep is to memory. "This is exciting because we're just starting to crack the nugget of sleep's role in memory," he said. Wilson said it's a long way from watching rats dream about mazes to arriving at elusive conclusions about how the mind works during sleep. "It will definitely be a challenge," he said. "But we have a pretty good idea of what is possible." Wilson's research is funded by the National Institutes of Health and the RIKEN-MIT Neuroscience Research Center.