How memories are stored in the brain has always been a mystery. It is thought that each memory is stored in the form of a group of brain cells (neurons), but it’s practically impossible to confirm that because those neurons are all over the place. We do know, however, that a brain region called the lateral amygdala (LA) is where fear memories are stored. Say you’re just a kid and your older sibling decides to make you watch Poltergeist (am I the only one who went through this?). During the really scary parts of the movie, your neurons in the LA make a ton of this protein called CREB (yet another acronym, it stands for cyclic adenosine monophosphate response element binding protein). That’s the tell-tale sign the researchers used to try to identify and then destroy the neurons responsible for fear memories.
They used an experiment called fear training (sounds like torture? Just think about all the people who willingly volunteered to be on “Fear Factor”). They put a mouse in a special cage, and then they play a tone. Right after the tone, the mouse gets a little shock on its feet. The mouse eventually catches on, and freezes when the tone is played (freezing behavior is how we know the mouse is scared). The really clever part of this experiment is that the researchers managed to engineer in the mouse a genetic switch that would selectively kill the neurons that made a lot of CREB (the ones presumably responsible for the fear memory). So after training the mouse to be scared of the tone, they flipped the switched on, the CREB-making neurons died, and voilà! The mouse forgot its fear of the tone and no longer freezes.
So, ok, researchers fried part of this mouse’s brain, and the mouse won’t freeze anymore. Sure, but will the mouse do anything anymore? I don’t know about you, but I’m picturing the mouse in a post-lobotomy state, drooling a little, unmotivated to do anything. Apparently not so. The researchers did a bunch of control experiments to show that the mouse could still run through mazes, store new memories, and even re-learn to be afraid of the tone, if properly trained. They also showed that if you just kill a bunch of random LA neurons (instead of just the ones that make lots of CREB), erasing memories doesn’t work.
So is this relevant? Well, it’s a great contribution to our knowledge of how memories are encoded and stored. A lot of people are excited about this because they see a potential therapy for post-traumatic stress disorder, but to be fair, applications in humans are very, very far down the road, regardless of what the movie “Eternal Sunshine of the Spotless Mind” suggests. If you had a choice, would you erase some bad memories of your past? How did those memories shape the person you are today?