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Select what you forget
Our daily life is filled with a lot of trivial information that we don’t benefit from keeping in memory. Moreover, some memories are short-term and can be updated over time – You could probably tell me what you ate yesterday, but what about 3 weeks ago? Probably not. Similarly, if you turn 37 years old this year, it would be redundant to remember that you were 36 last year. Finally, there are memories associated with high levels of stress. Those memories are harder yet even more important to forget, or at least make less vivid over time. These are a few examples showing that forgetting is crucial, contrary to popular beliefs that present it as an adverse side effect of time.
Remember the future
Try to picture this, your brain is like an electrical network with a limited number of wires. Within this circuit, electric signals flow along the wires, carrying information. As we learn and experience more of the world, we need to store increasingly complex information. And at the same time, sensory input continues to come in. This is an infinite collection of information we’re talking about. Therefore, you can imagine that, soon, memory is full of items, saturated, making it impossible to keep track of everything!
Fortunately, brain machinery has its own way to select what is relevant from what is not based on the context. The objective is to sort and generalize information – that is, to take a bunch of experiences and figure out the general rule that can explain them all. Any element of a memory that is not essential to its understanding has to remain in the background or even be forgotten. For example, a kid learns from experience that there’s always time for a bedtime reading before going to sleep. However, the story differs each night, ranging from fairytales to music books, and so does the storyteller – imagine that sometimes it’s mom or daddy and occasionally his big sister. Then, learning a general rule based on these repeated experiences requires him to find the information that they all have in common: “someone will tell me a story every night”. The rest is just contextual background and remains secondary. We call this generalization process statistical learning and it’s very practical for predicting what could happen in the future while keeping some sense of flexibility (things are never exactly as we expect).
Emotion makes it harder to forget
Nonetheless, it surely occurred to you that, sometimes, you remember non-essential details and you don’t understand why. Like the color of your socks on the day when you adopted your dog, Larry. Let’s try to understand why then. We definitely agree on the fact that knowing the color of your socks, in itself, isn’t highly exciting, and that you’d probably benefit from not remembering it at all. However, by association, any information that reminds you of that first-time-you-met-your-dog day is special and marked with a positive value, making it hard to forget. So, the fact that you remember the socks and the first song that you and Larry heard in the car while going back home, is a direct consequence of the emotions associated with that memento of yours.
Although forgetting is vital, it is not clear what it means concretely in terms of mental representations. Memories are highly plastic, and their form and content evolve in time in many different ways, depending on how general or emotional they are. But what happens to the forgotten memories concretely? Recent research suggests that, more than a passive weakening of the neural network supporting a given memory, forgetting involves active neural mechanisms.
Image: Umberto via Unsplash