WASHINGTON It's a tough life being a laboratory rat -- being made to run maze after maze, for hours on end, with only a few chocolate sprinkles as pay.

In fact, it's such a demanding job that the rats actually dream about it, researchers said.

"We know that they are in fact dreaming and their dreams are connected to actual experiences," Matthew Wilson of the Center for Learning and Memory at the Massachusetts Institute of Technology, who led the study, said in a statement.

Writing in the journal ***Neuron***, they said their findings were not only fascinating but could shed light on what dreams do for humans.

Wilson and graduate student Kenway Louie taught the rats to run around a circular track in exchange for treats.

"We give them little chocolate sprinkles -- little decorator sprinkles. They like that," Wilson said in a telephone interview.

They implanted tiny electrodes in the rats' brains -- an procedure that scientists say is painless and allows them to monitor the activity of individual neurons.

They focused on the hippocampus, which is the part of the brain where, in humans, memories of experiences are formed.

They monitored the rats' brain activity while they ran the maze, and then monitored what the brains did when the animals slept. Like all mammals, including humans, rats go through phases of rapid eye movement (REM) sleep, which in humans correlates with dreaming.

The patterns were so similar that the researchers could tell where on the maze the rats were in their dreams and how fast they were dreaming they were running.

"We could identify what segment and what the pattern of the running activity was during this REM sleep -- literally what they were doing -- how they were running, where they were running," Wilson said.

"Remarkable and Amazing"

"It's remarkable and amazing to us. I can tell you the first time I saw this it was the most amazing thing I had ever seen -- the pattern of firing of cells in the brain," he said.

Wilson believes the rat dreams have a purpose. Research has shown that humans and other animals learn -- even tasks -- better when they literally sleep on it.

The rat work suggests dreams may be a literal rehearsal.

"We believe the reactivation of memory during sleep has some importance in the formation of memories," he said.

It also shows that the brains of rats are more complex than had been believed. The dream sequences lasted for minutes at a time. Scientists had not known whether lower animals such as rodents could recall such long sequences of events.

"I think it does force us to think about animal cognition," Wilson said.

(Reuter)