Where do our memories disappear to, and how can they be retrieved?
We tend to think that a forgotten memory is like a file permanently deleted from a computer, but scientists have discovered that reality is much more complex. A new study published in the scientific journal Nature Neuroscience shows that in fruit flies, memories we thought had disappeared completely actually remain hidden deep in the brain, ready to come to life as soon as we receive the right trigger or cue.
We tend to think that a forgotten memory is like a file permanently deleted from a computer, but scientists have discovered that reality is much more complex. A new study published in the scientific journal Nature Neuroscience shows that in fruit flies, memories we thought had disappeared completely actually remain hidden deep in the brain, ready to come to life as soon as we receive the right trigger or cue.
To test how memory works, the researchers trained fruit flies to associate a certain smell with a mild electric shock, which caused the flies to stay away from that smell. After one day, the memory seemed to have been erased and the flies returned to approaching the smell. However, when the researchers returned the flies to the exact same room where they underwent the training — with the same smell, the same texture, and the same lighting — the memory suddenly awakened and the flies fled immediately.
An examination of brain activity proved that when the flies "forget," the memory does not disappear, but moves to a hidden and quiet neural system that does not activate the usual orientation. As soon as all the environmental cues connect together, the brain transfers the information back to the original path and the memory surfaces.
However, this process is not perfect: when the researchers used a different, innocent smell as a cue, the flies became confused and began to avoid it as well, as if it had always been dangerous. In other words, the attempt to reconstruct the memory caused the brain to mistakenly create a completely false memory.
The brain's ability to keep a secret backup of forgotten information was partially known, but now scientists understand that the brain creates two versions of all our memory experiences in advance — one that is active immediately, and another that is kept secret in case of need. Although the experiment was performed on flies and not on humans, the researchers believe it provides a fascinating glimpse into how the human brain also manages to store forgotten memories, and why our memories are so susceptible to distortions and errors.
