Lost Thoughts in the Wake-Sleep Transition

I've been meaning to write about this curious phenomenon I experience every time I go to sleep. Lying in bed last night, I was thinking about a movie I had just finished watching - The Aviator, a great movie! - and was overcome by a sudden frustration: some idea that was running through my mind had simply vanished, to be replaced by something silly and mundane. Trying desperately to remember what I had just been thinking about, I could find no trace of my thoughts. It was as if they were never recorded. This happens several times, until I finally give up and fall asleep. Even more perplexing is that I am aware of those lost thoughts, I know something is missing. I just can't remember what it was. If these aren't freak phenomena, one can imagine something in the awake-sleep transition that messes with short term memory. It's as if whatever network or assembly representing the would-be memory doesn't undergo short term plasticity necessary to "solidify" those connections. This is of course overly simplistic and probably misleading language, but a way to think about it. Perhaps this can (or has been?) analyzed in rats, as in the "replay" or reactivation activity in hippocampus of experienced events, during sleep, as in this paper by Matt Wilson of MIT. One could examine lost thoughts in the awake-sleep transition by looking at the temporal structure of activity during that transition vs. same activity during experience on a maze, for example. Perhaps this loss of thought depends on some subcortical "kick" that's absent during sleep. Just a thought.