This is all fascinating stuff. I love the idea behind memory palaces, and this stuff about place/grid cells sounds like the explanatory science behind it. Any reading you'd recommend?

> And clearly we humans forget many of the sounds we have heard (e.g. songs, lyrics).>

It's true we forget many sounds, but songs and lyrics is a curious example. I'd guess those were high on the list of things humans are good at remembering… maybe #4 behind places, faces, and language in general? I've had pop lyrics and commercial jingles and theme songs rattling around in my head for decades, and I can easily sing them word for word. Something about a sequence of words put to a beat and a melody just seems to stick.