You Want to Make a Memory?

The melody of the same name, sung by Bon Jovi, is a great song. I’m pretty sure Jovi wasn’t thinking of physically implanting memories into somebody’s brain when he sang that tune though. After all, why would he? Memories are the result of the past, of personal experience. Well, that is true no longer thanks to optogenetics and a skilled research team at MIT.

Optogenetics is a promising field where genes that confer light responsiveness are inserted into the DNA of cells. Ultimately, it allows researchers to trigger and control the activity of neurons and brain circuits with light. Quite literally, neurons can be turned on or off by the flip of a switch. Now light obviously can’t penetrate the skull, so it must be exposed directly to the brain. Mice who are studied using this technique look a bit like this:

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Using optogenetics, MIT researchers were able to plant false memories (called incepting) into the brains of mice and, and the mice successfully recalled an event that never occurred. The technique is a bit complex; they actually engineered the hippocampal cells of mice to express the gene for channelrhodopsin, a protein that will activate the cells when exposed to light. They then modified channelrhodopsin so that it would be produced whenever a gene called c-fos, which is necessary for memory formation, was turned on. Essentially, as a memory was forming, the c-fos gene was turned on, causing channelrhodopsin to be expressed as well. The result was that the cells that encoded certain memories were labeled with the light-sensitive proteins.

Let’s get into the experiment. The researchers placed mice in a chamber (A) and did not deliver any shocks. As the mice explored the chamber, the memories were stored in cells that were labeled with channelrhodopsin. The subsequent day, the mice were placed in a different chamber (B) and given a mild foot shock. At the same time as the foot shock, the researchers used light to activate the neurons encoding the memory of chamber A. Finally, the mice were placed back in chamber A, where they now froze in fear even though they had never been shocked there; a false memory had been incepted. The scientists were actually able to make the mouse remember an event that had never happened – being shocked in chamber A- and reacting fear in the same way it would if the memory was real.

Pretty cool huh? Scientists hope that this will help them understand one of the difficult aspects of human memory- its unreliability. False memories have gained notoriety for how common they occur in the countroom, with eyewitnesses sending innocent people to prison. Hopefully better understanding of false memories may help with decisions involving eyewitness testimony, and prevent the incarceration of innocent people.

If you want more information on this experiment, and optogenetics, check out these cool videos!

Sources:

http://newsoffice.mit.edu/2013/neuroscientists-plant-false-memories-in-the-brain-0725

http://www.bostonglobe.com/news/science/2013/07/25/mit-scientists-plant-false-memory-mouse-mind/dEHuCh1RYrWFCsscJG7WPO/story.html

Liu, X., Ramirez, S., & Tonegawa, S. (2014). Inception of a false memory by optogenetic manipulation of a hippocampal memory engram. Philosophical Transactions of the Royal Society B: Biological Sciences, 369(1633), 20130142.

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