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Researchers retrieve "lost" memories in mice

Xinhua, May 29, 2015 Adjust font size:

Memories that have been "lost" as a result of amnesia can be retrieved by activating brain cells with light, a study in mice suggested Thursday.

The findings, published in the U.S. journal Science, may help answer a fiercely debated question in neuroscience as to whether memories lost to amnesia are completely erased or merely unable to be recalled.

"The majority of researchers have favored the storage theory, but we have shown in this paper that this majority theory is probably wrong," Susumu Tonegawa, a professor at the Massachusetts Institute of Technology, said in a statement. "Amnesia is a problem of retrieval impairment."

In the new study, mice were first trained to associate a mild foot shock with a specific environment, known as chamber A, eliciting a typical "freezing" behavior. Eventually, trained mice would freeze in chamber A even without the shock.

Brain cells activated during memory formation were genetically labeled with a blue light-sensitive protein to allow their visualization and reactivation.

Then, some mice were given a chemical called anisomycin to induce retrograde amnesia, which follows traumatic brain injury, stress, or diseases such as Alzheimer's in humans. Other mice received saline as a control.

As expected, amnestic mice did not freeze after returning to chamber A, indicating that they could not recall the memory for the specific association of the chamber and the mild foot shock.

Next, the mice were put in a novel, neutral environment called chamber B and a technology involving using blue light pulses was used to selectively activate brain cells that were genetically labeled during their training in chamber A.

When the cells, collectively called a "memory engram," were activated, the amnestic mice froze again, just as the control mice, the researchers said.

"Our conclusion," said Tonegawa, "is that in retrograde amnesia, past memories may not be erased, but could simply be lost and inaccessible for recall."

Taken together, these findings "provide striking insight into the fleeting nature of memories, and will stimulate future research on the biology of memory and its clinical restoration," he added. Endite