Isn’t it astonishing that brain is performing this task? How can it do it? The memory that is highly likely to be needed in the future, should be kept. The one that’ll soon become irrelevant should be deleted. But we don’t know the future. Then how is it possible to decide which memory to delete?
The answer is actually not that difficult. It is predicting the future. There is a theory that brain is just a prediction machine (embodied cognition). It wants to predict all the signals thats being thrown at it. Looks like it has a perfectly plausible reason to do so. Brain only has a limited amount of resource in it. It has limited memory and limited action capacity. It can look only into a smaller area into a signal. So focus and attention is important. It can remember only a finite amount of things. So it is important to encapsulate a chain of events into a single entity — creating abstract concepts. Is consciousness is just an effect of these actions? How brain actually does it?
One way is definitely time and usage depended. The memories that were not used for a while is less likely to be used again in future. This method helps us to understand why it should be easier to memorize something by repetition. But it is not difficult to understand that this can’t be the only method. Because this requires all the information to enter into the brain and the filter out the unwanted things gradually through time. That doesn’t happen always. Brain filters something out right from the sensors. For example, I’m typically reluctant to memorize phone numbers. I just don’t pay attention to the numbers to begin with. From this habit, once I thought I can’t memorize numbers. But then I did a few experiments on myself and found that I can memorize numbers if I want to — which I don’t.
So looks like keeping or deleting the correct memory has something to do with higher levels of cognition. Can it be that the purpose of cognition is to actually resolute for which memory to keep and which one to delete?