Friday, July 26, 2013

Tracing Memories Of Things That Never Happened

In the research reported Thursday, Dr. Tonegawa’s team first put mice in one environment and let them get used to it and remember it. They identified and chemically labeled the cells in the animals’ brains where that memory was being formed. The mice were not shocked in that environment.

A day later, in a completely different environment, the researchers delivered an electric shock to the mice at the same time that they stimulated the previously identified brain cells to trigger the earlier memory.

On the third day, the mice were reintroduced to the first environment. They froze in fear, a typical and well studied mouse behavior, indicating they remembered being shocked in the first environment, something that never happened. The researchers ran numerous variations of the experiment to confirm that they were in fact seeing the mice acting on a false memory.

The tools of optogenetics, which are transforming neuroscience, were used to locate and chemically label neurons, as well as make them susceptible to activation by blue light transmitted by a fiber optic cable. With these techniques the researchers were able to identify and label which neurons were involved in forming the initial memory of the first environment, and to reactivate the labeled cells a day later with light.

Dr. Tonegawa said that because the mechanisms of memory formation are almost certainly similar in mice and humans, part of the importance of the research is “to make people realize even more than before how unreliable human memory is,” particularly in criminal cases when so much is at stake.


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