Hi. You may only understand what I am going on about here if you play an instrument. I have often noticed that there are songs that I really love and know inside out, which, in my mind, I can play almost perfectly in my head; most of the parts and certainly all of the melodies etc. But then, I pick up my guitar and try to play the parts from memory, and I get nowhere! It's almost as if when I was playing that song in my head, my mind was tricking me into thinking that I knew the whole song inside out, when I didn't, or that my mind has a good grasp of the song and the general sound, but can't recall the general notes. Has anyone else experienced this, or have other examples? It's pretty vexing and unassuring to think that there are lots of things that you think your brain knows well but it doesn't. On the other hand, maybe this is a really nice example of the brain seemingly retaining quite strong memories, but compressing them and leaving out details (I know the brain isn't a hard drive, but you know what I mean). I find this really quite interesting. Maybe when they figure out how the brain works (http://news.bbc.co.uk/1/hi/technology/8164060.stm), this might lead to new advances in file compression or something!