The big question is, do sheepdogs dream of counting sheep?

Animals have complex dreams much like humans, the American Association for the Advancement of Science was told yesterday. A study has shown that even laboratory rats spend much of their sleep dreaming of things they do when they are awake.

Any pet owner knows dogs and cats seem to dream but researchers have demonstrated beyond doubt that animals regularly "relive" important events that they do during the day.

The experiment, by scientists at the Massachusetts Institute of Technology, involved training rats to run a maze in a particular way, and monitoring the "firing" of electrical impulses generated by their brain cells as they did. Then they studied the animals' brain activity when they were asleep and found a repeat of the unique signature of brain activity created in the maze.

"We know they are dreaming and their dreams are connected to actual experiences,"Dr Matthew Wilson told the American Association meeting in Boston. "No one knew for certain that animals dreamt the way we do, which can involve replaying events or at least components of events that occurred while we were awake."

Similar techniques could be used on animals and humans to understand why we need to dream, which appears to be an essential prerequisite of a good night's rest. They could also help us to understand the changes in the brain linked to disorders such as Alzheimer's disease and memory loss, Dr Wilson said.

It has been a century since Freud brought forward the study of the subconscious and the examination of the content of dreams as a tool for understanding the nature of cognition and behaviour in humans," Dr Wilson said.

"We now have the means to bring this world of dreams into the study of animal cognition, and by doing so gain a deeper insight into our own."

The rat study showed the animals had about 40 episodes of dream sleep, called rapid eye movement, monitored by scientists with extreme precision. "The correlation is so close the researchers found that as the animal dreamt, they could reconstruct where it would be in the maze if it were awake and whether the animal was dreaming of running or standing still," Dr Wilson said.

Dreams could also represent an opportunity for us to continue to work on a problem while we are asleep, he added. Some people report that after a night of dreaming they can find the solution to something that has been puzzling them.

"Replaying pleasant or unpleasant experiences may allow us to learn what these had in common and use this to guide future behaviour," Dr Wilson said. "This work demonstrates animals are capable of re-evaluating their experiences when they are not in the midst of them."