Well, this question doesn't seem to be so easily responded at first. Memory is a quite complicated process, as it's depicted through this photo. There're many different steps and stages going on within the grey matter and thus, testing our intelligence quotient (IQ) may vary to a greater extent, depending on the assessing criteria to be applied.
On the contrary, our mental capacities can be trained and improved. However, this is not only a question of numbers, tests or IQ, but taking into account that our brain is similar to another muscle of our entire body, though it's true that we need the right stimulations and environment to obtain our best potential and develop more talents and capacities. Finally, to quote an example, I'd like to recommend you to look for some information about Sir Ken Robinson. Here's a well-known video by him: