Are our memories ever really gone or do they just hide away deep down in our memory? Revolutionary research at the Massachusetts Institute of Technology (MIT) reveals that with a certain type of stimulation, long-lost information can be reactivated.
Do you know the feeling of trying to remember something, the name of a band or a geographic term, and having it on the tip of your tongue but you just can’t seem to recall it? Knowing that the information is there in your mind, you just can’t seem to grasp it. This unpleasant phenomenon could be the key in explaining, how we memorise and recall information.
How do we recall information?
We only become aware of our memory when it leaves us hanging. Scientists are interested in examining memory in situations and in diseases in which it doesn’t work properly. Such diseases are, for example, Alzheimer’s disease and severe brain concussions. There are two theories that explain why humans suffer from memory problems or losses: The first and most well-known theory states that information in memory simply gets lost due to inflammatory processes related to diseases. The other theory says that any content in our memory is always there and intact but it is our ability to retrieve this memory that is dysfunctional. The following experiment was constructed to find out which theory is right.
The experiment, which was published in the journal Science, was conducted with mice, and it was divided into 5 parts:
1. The mice were put in a cage: In this cage they were subjected to electric shocks. Previous studies have shown that mice remember the cage in which they experienced negative emotions. If they were put in this same cage again, they would experience fear and panic reactions. Scientists believe this to be part of a type of learning performance.
2. The mice were injected with a substance called Anisomycin: This substance can cause human diseases like Alzheimer’s in animal bodies by paralyzing so-called ‘Memory engram cells’. Scientists believe these cells are responsible for recalling memories from the long-term memory. Anisomycin disrupts the retrieval of information from the memory.
3. The memory performance of the mice was examined: The mice were once again put into the cage, in which they were subjected to electric shocks. Now, however, because of the injection of Anisomycin, they didn’t show any recollection of what had happened to them earlier in this cage. That is, the mice did not remember having been in that same cage before, and they also didn’t have any recollection of the painful electric shocks they had to endure in it.
4. Optogenetic stimulation of ‚Memory engram cells‘: Scientists found an unprecedented method to switch chosen brain areas on and off. What sounds like a science fiction movie is in fact reality. The way this works is through a particular light, or rather a specific ray of light, which targets and activates the so-called ‘Memory engram cells’ that had been paralyzed with Anisomycin before.
5. The mices’ memory performance was examined once again: With their now activated ‘Memory engram cells’, the mice were once again put into the cage (see phase 3). And the results were what the scientists expected: Because of the activation of the ‘Memory engram cells’, the mice were able to retrieve information in their memory that they had not been able to access before. This means that the information that was completely lost to them, was all of a sudden back, reactivated, and ready to be retrieved.
Saving long-lost information
The experiment shows that learning processes still happen even when a person cannot actively remember an experience. With diseases like Alzheimer’s, it is not the memory that is lost but rather the recalling of memory that is hindered. In these cases the cells that are responsible for recalling information are disrupted. The findings give hope to the future treatment of Alzheimer’s and similar diseases. Hopefully, it will be possible to artificially reactivate the ability to recall forgotten information, and counteract the damaging effects of Alzheimer’s disease and others. As you see, even after all this past research, our brain is still full of surprises. And the journey to discover it has only just begun.
1: Ryan, T. J., Roy, D. S., Pignatelli, M., Arons, A., & Tonegawa, S. (2015). Engram cells retain memory under retrograde amnesia. Science, 348(6238), 1007-1013.