[Editors] MIT: New insights on animal dreams

[Elizabeth Thomson]

MIT News Office
Massachusetts Institute of Technology
Room 11-400
77 Massachusetts Avenue
Cambridge, MA  02139-4307
Phone: 617-253-2700
http://web.mit.edu/newsoffice/www

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MIT: New insights on animal dreams

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For Immediate Release
MONDAY, DEC. 18, 2006
Contact: Elizabeth A. Thomson, MIT News Office
Phone: 617-258-5402
Email: thomson at mit.edu

CAMBRIDGE, Mass.--Memories of our life stories may be reinforced 
while we sleep, MIT researchers report Dec. 17 in the advance online 
edition of Nature Neuroscience.

Matthew A. Wilson, professor of brain and cognitive sciences at MIT's 
Picower Institute for Learning and Memory, and postdoctoral associate 
Daoyun Ji looked at what happens in rats' brains when they dream 
about the mazes they ran while they were awake.

In a landmark 2001 study, Wilson showed that rats formed complex 
memories for sequences of events experienced while they were awake, 
and that these memories were replayed while they slept-perhaps 
reflecting the animal equivalent of dreaming.

Because these replayed memories were detected in the hippocampus, the 
memory center of the brain, the researchers were not able to 
determine whether they were accompanied by the type of sensory 
experience that we associate with dreams-in particular, the presence 
of visual imagery.

In the latest experiment, by recording brain activity simultaneously 
in the hippocampus and the visual cortex, Wilson and Ji demonstrated 
that replayed memories did, in fact, contain the visual images that 
were present during the running experience.

"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.

Reinforcing memories
By recording the spiking patterns of electrodes in individual neurons 
in the rats' brains, Wilson is able to compare the activity of the 
neurons when the animal is awake and asleep. It turns out that 
neurons activated when the animal experiences an event while awake 
are reactivated during sleep.

In addition, the region of the cortex that processes input from the 
senses and the hippocampus "talk" to each other during sleep, leading 
researchers to speculate that this process reinforces and 
consolidates memories.

But research to date lacked specific evidence that episodic 
memory-times, places and emotions related to events that make up our 
life stories-is reinforced in the cortex, the hippocampus or both 
during sleep.

For the first time, this work shows that the brain is replaying 
memory events in two locations at once-in the visual cortex and in 
the hippocampus.

"These results imply simultaneous reactivation of coherent memory 
traces in the cortex and hippocampus during sleep that may contribute 
to or reflect the result of the memory consolidation process," Wilson 
and Ji wrote.

This work is supported by the Brain Science Institute at the 
Institute of Physical and Chemical Research (RIKEN) in Japan and the 
National Institutes of Health.

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