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Scientists give mice false memories

Optogenetics uses light to explore the brain by labeling certain cells

CNN News Wire | 7/25/2013, 12:54 p.m.

Imagine you’re a mouse, and you’re freaking out right now because a researcher is putting you into a chamber. You distinctly remember feeling shocks to your tiny feet in that chamber.

What you don’t know — cue the creepy music — is that scientists have manipulated your memory by tinkering with your brain cells, giving you a false version of your own past. The truth is that, in this particular chamber, you were never actually shocked.

This sounds like a horror film, but it actually happened in a laboratory setting. And the research being done there could have implications for understanding memory in humans.

Scientists say they have, for the first time, generated a false memory in an animal by manipulating brain cells that encode that information. They published their findings this week in the journal Science.

What’s more, the researchers say, the cellular events involved in the formation of a false memory resemble what takes place in forming a real memory. This jibes with the fact that humans who have false memories of events that didn’t happen firmly believe that those memories are real.

“We should continue to remind society that memory can be very unreliable,” said the study’s senior author, Susumu Tonegawa, director of the RIKEN-MIT Center for Neural Circuit Genetics, a collaboration between institutions in Saitama, Japan, and Cambridge, Massachusetts.

Controlling the brain with light

The lucky mice who participated in this study underwent a brain exploration technique called optogenetics, a means of manipulating individual brain cells with light. Optogenetics was invented by MIT professor Ed Boyden and Stanford professor Karl Deisseroth. It’s an innovative approach to understanding the brain that is being widely explored in labs throughout the world and could eventually lead to better treatments for a variety of brain conditions.

Tonegawa’s team started by identifying cells in the hippocampus, a seahorse-shaped brain structure that encodes a memory for a particular experience.

Then they “labeled” these information-rich cells, genetically altering them with a light-sensitive protein called channelrhodopsin. As a result, shining a blue light on these cells activated them.

In a 2012 study reported in Nature, Tonegawa and colleagues used this method to show that they could activate a mouse’s memory through light. They put each mouse in a chamber and gave it a foot shock. Then they genetically altered the brain cells corresponding to the memory of being shocked in that chamber.

When they put a mouse in a different chamber, the mouse did not show a fear response. But when they shone a blue light on the mouse whose memory cells had been genetically altered, that mouse froze up in fear, because the memory from the first chamber had been activated.

“We artificially replaced the natural recall cues with the light,” Tonegawa said.

The new study

The researchers took this one step further in the in the new study described in Science. They showed that if you can activate particular brain cells using light, and those brain cells contain memory information, then you have the power to make an animal believe it experienced something that never actually happened.