Even rats may dream in pictures, study finds
Dec 22,2006 00:00 by World-Science.net

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.