The notion of idea density, as I understand it, has to do with associational networks/clouds of ideas, and the navigation therethrough. Its plausible, although I don't know what kind of research exists here, that such networks qua memory banks may experience a certain atrophy in the prolonged absence of exercise.
But then again, my psychologist friend who is also fond of wordle and worldle says that his success in the latter game - which is about trying to guess the daily country, then getting feedback in the form of distance and direction away from the correct answer - is attributable to long-term memory, as he was very much into maps as a child.