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Even rats may dream in pictures, study finds
Dec. 19, 2006
By Deborah Halber/MIT News Office
and World Science staff
Researchers have reported
what they say is some of the strongest evidence to date that animals, like humans,
have dreams with images. A "dreaming"
rat. (Courtesy MIT)
Matthew A. Wilson and Daoyun Ji
of the Massachusetts Institute of Technology in Cambridge, Mass., examined what happens in rats’ brains
as they “dream” about mazes they ran while awake.
In a previous study five years ago, Wilson found that rat brain cells replayed some of the same activity patterns in sleep as they did while running a maze. The scientists reasoned that this might reflect dreaming about the maze.
But at that time, the researchers couldn’t say whether images accompanied the replays.
This is because the reenactments were found to occur in the brain’s memory center, the hippocampus, not in specifically visual areas of the brain.
In a new experiment, Wilson and Ji recorded brain activity simultaneously in the hippocampus and the visual cortex,
a key vision center of the brain. They found what they described as strong evidence that the replayed
memories did contain pictures.
“This work brings us closer to an understanding of the nature of animal dreams and gives us important clues as to the role of sleep in processing memories of our past experiences,” Wilson said.
Evidence that animals dream, even vividly, is not
a new phenomenon. Cats with certain types of brain damage chase imaginary mice during the sleep stage associated with
dreaming in humans, called rapid eye movement sleep.
Wilson records the electrical signaling of individual brain
cells to compare their activity in sleeping and waking. He
also investigates how this activity may help cement memories
in place, as dreams are theorized to do. The new work shows that the brain replays memories in two places at once—in the visual cortex and hippocampus, he said.
These activities “may contribute to or reflect the result of the memory consolidation process,” Wilson and Ji
wrote in the study. It appeared in the Dec. 17 advance online edition of the research journal
Nature Neuroscience.
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Animals, like humans, may dream in pictures, researchers have found in a new study. The scientists, with the Massachusetts Institute of Technology in Cambridge, Mass., reported the findings in the Dec. 17 advance online edition of the research journal Nature Neuroscience. MIT’s Matthew A. Wilson and Daoyun Ji examined what happens in rats’ brains when they dream about mazes they ran while awake. In a 2001 study, Wilson found that rat brain cells replayed some of the same activity patterns in sleep as they did while running a maze. The scientists reasoned that this might reflect dreaming about the maze. But these replays were found in the brain’s memory center, the hippocampus, not in specifically visual areas of the brain. Thus the researchers couldn’t say whether images accompanied the apparent maze reenactments. In a new experiment, Wilson and Ji recorded brain activity simultaneously in the hippocampus and the visual cortex, the brain’s vision center. They found what they described as strong evidence that the replayed memories did contain pictures. “This work brings us closer to an understanding of the nature of animal dreams and gives us important clues as to the role of sleep in processing memories of our past experiences,” Wilson said. By recording the electrical patterns of individual brain cells, Wilson compares their activity in sleeping and waking. He has found that cells activated when the animal experiences an event while awake are reactivated during sleep. The new work shows that the brain replays memories in two places at once—in the visual cortex and hippocampus, he said. These activities “may contribute to or reflect the result of the memory consolidation process,” Wilson and Ji wrote.