Knowledge accumulation or substitution?

Can you retain all you have learnt from your first day of life till today? I don't think so.
At least I cannot. I know many people who have an extraordinary memory. This helps them so much, as we are living in the era of over information. They can access to such a huge quantity of memories. My assumption here is that you cannot accumulate knowledge, and that while learning new concepts or notions you will finally substitute pre-existing ones in our memory with the fresher ones.
I would refer to this phenomena as the enlightening of knowledge, as if knowledge were something available outside of ourselfs. I like to use this metaphor because it reminds me of the Vattimo's philosophical theory. Gianni Vattimo says (and I apologize not being a philosopher and thus not being able to discuss this topic in a proper way) that history is not a linear evolution of events, but the collection of illuminations of the very being, while outside the light there is no continuity. Now from my perspective, a similar thing happens to each of us while talking about knowledge. If knowledge is the history of our life, we can enlight just some part of it, but not the totality of it. This is because our brain has limits in retaining and retrieving information. Those people who are blessed with this gift of retaining little memories, have the power of concentrate on their senses. This is something that I would like to demonstrate. I have always been convinced that Art has its strenght not in the technique itself but in the ability of listenning and interpreting our senses, that some artists do have. Knowledge accumulates itself outside of our brain in books, pictures, electronics devices, etc. Anyway this is of little relevance, as we cannot retain all this information at the same time. Those people who understand this would have much more creative power than those trying to repeat by heart what they have learnt.