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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.

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. 

A "dreaming" rat. (Courtesy MIT)


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.