Why do songs trigger certain memories of mine?

just so you know starlight by muse is an awesome song. lol.. thiis happens to me often as well. i think its because the first time you hear a certain song, if you are usually with somebody, somewhere or someplace, and then when you hear the song again you begin to remember that certain time in your life when you heard it. its just a "impression of the song"..i dont know.. hope this helps.