That's interesting.. I wasn't aware this was studied. I stopped drinking years ago because I noticed that alcohol reduced the amount of code I could hold in my head, even up to a week later.
I don't think there's a good answer to this... it varies depending on the language, familiarity of the codebase, complexity, novelty/difficulty of the problem/solution, how repetitive the code is, etc. So I don't think comparisons can be made between people, even if they're looking at the same code base (since what is difficult for me, may be easy for you, and therefore easier for you to comprehend and remember... but if we look at another codebase, the opposite may be true.)