There have been lots of stories about how unreliable memory can be, such as people ‘remembering’ things that never happened when testifying in criminal trials. But those were fake memories that people made for themselves. Now scientists have created fake memories in rats. They have even gone one step further and then deleted these memories and re-implanted them. I don’t know about you, but that sends chills down my spine. Memory can now be externally manipulated. Luckily we don’t need to worry about Big Brother changing our memories while we sleep just yet. This has only been done in rats that were genetically engineered to have a light sensitive protein in their brain cells (neurons). When this protein was activated by light it altered connections between neurons that process fear and neurons that process sound to create a false memory.
Scientists often test memory in animals by associating a sound with something unpleasant, like a mild electrical shock. The animals then learn to show fear when they hear this sound even when there is no shock. In this study, scientists used light to activate the brain’s sound centre and make the rats think they heard a sound right before getting a shock. So the rats became afraid of a sound they never heard. They now had a false memory. Scientists went on to use a different pattern of light pulses to weaken the neuronal connections. After this the rats didn’t remember to be afraid. Then they repeated the original light activation to re-strengthen neuronal connections. The rats were afraid again. Scientists could create and delete this false memory at will.
They could also stop rats from remembering something that really happened. A second group of rats was exposed to a real sound coupled with a shock. Then they were treated with light pulses to weaken neuronal connections. These rats did not show fear when they heard that sound again. They could not remember that a shock usually came after that sound.
The point of this study was not to creep us out, but to prove that memories really are caused by increased strength in connections between neurons. This is called long term potentiation. It’s long been thought that this was the molecular basis of memory but this Frankenstein-ish experiment finally proved it.
The Scientific Paper