How the Brain Makes Space for New Memories: By Erasing a Few Old Ones
Forgetting an umbrella or the location of a parking spot may be annoying, but scientists have suggested that for healthy brains to function well, they need to forget. By forgetting, scientists say, the brain makes space for new memories. In an intriguing breakthrough, researchers from the United States and China have identified the protein responsible for forgetting in fruit flies. By tweaking a protein called Rac, researchers were able to speed up and slow down the erasure of painful memories [New Scientist]. The findings were published in the journal Cell.
Scientists have been unable to pinpoint why people forget. Some have suggested that new memories are ephemeral and vanish over time, while others thought that interference caused earlier short-term memories to be overridden as new information comes in [Science Daily]. While both of these notions seem to suggest that forgetting is a passive mechanism, the new study suggests that forgetting is far more active, and that Rac works to inhibit the formation of more long-term memories.
The scientists studied fruit flies that were exposed to two fly-repellent odors, the second of which came with an electric shock. The flies quickly learned to head to the odor that didn’t cause them pain. Then the scientists switched the set-up, linking the first odor to the shock instead. Regular flies quickly noted the change, discarding the old memory of which odor came with a shock and learning to head towards the now-safe second odor. But when the experiment was repeated after the memory-eroding protein [Rac] was blocked, there was utter confusion. The flies had not erased their first memory, and had made a second memory. Unable to pick which odor to fly toward, they zigzagged back and forth [The New York Times].
The researchers determined that when Rac was switched on, newly formed memories faded fast, allowing new memories to come in and solidify. When Rac was switched off in the fruit flies, new memories lingered longer, extending from the normal limit of just a few hours to more than a day.
The scientists next hope to test the effects of meddling with the proteins in mice. If this mechanism holds true in mammals, it could shed light on the molecular basis of forgetting in humans [New Scientist], as humans also have the Rac protein. The researchers suggest that the identification of this protein could potentially help create techniques to enhance cherished memories or to forget painful episodes, which could be a boon to those who suffer from post-traumatic stress disorder (PTSD). Until now approaches to erasing unwanted memories have largely focused on interfering with the laying-down of memories, rather than our natural ability to forget [New Scientist].
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