Rats 'can dream just like humans'
Scientists have peered into the dreams of rats and discovered they can be as complex as those of humans.
Researchers were able to pinpoint when rats were dreaming about running around a circular maze in search of a food reward.
By monitoring their brain activity, they were able tell where the animals would be in the maze had they been awake, and whether they were dreaming of running or standing still.
While dogs and cats often seem to dream, and studies have shown that mammalian brains follow the same series of sleeping states, this is the first research to indicate what animals are dreaming about.
Dr Matthew Wilson, from the Centre for Learning and Memory at the Massachusetts Institute of Technology, Boston, said: "No one knew for certain that animals dreamed the way we do, which can involve replaying events, or at least components of events, that occurred while we were awake.
"We looked at the firing patterns of a collection of individual cells to determine the content of rats' dreams. We know that they are in fact dreaming and their dreams are connected to actual experiences."
Dr Wilson told the annual meeting of the American Association for the Advancement of Science how his team first trained rats to run along a circular maze for a food reward.
They monitored the animals' brain activity during the task and when they were asleep. As each rat ran, its brain produced a distinctive pattern of neurons firing in the hippocampus, a brain region known to be involved in memory.
The rats' brain activity was again recorded during REM (rapid eye movement) sleep - a sleep phase which in humans is when most dreaming occurs.
In about half of more than 40 episodes of REM sleep examined, researchers found a repeat of the unique signature of brain activity created as the rats ran in the maze. The correlation was so close that it was possible, as an animal dreamed, to reconstruct where it would be in the maze if it was awake and how it would be moving.
Story filed: 13:27 Tuesday 19th February 2002