It follows from my anecdotal experiences that flashbacks are a useful function of the brain and not related to an externally induced psychoactive experience. Not related in any way other than these experiences can be extreme. It is useful, in order to survive, to be able to 're-experience' events at the extreme tolerances of our emotional scales. I believe many of us feel the same about flashbacks being a construct of the brain and also being useful.

For me, and I'm sure many of you, I use a bit of reinforcement in the sense of Pavlov. I listen to the same song at the onset of all of my journeys, except lucid dreams. This helps me channel the emotions and slight visuals of these times, but only when the song manifests organically. Unfortunately it is rare for this to work when I seek the song out. It works especially well if I have over-indulged in alcohol (but not to a point of oblivion), mmj, am tired, hungry or any combinations of them all.

I have to say, when it does happen it is great. Not do to the effect it produces but because it is a randomly pleasant experience that has been offered. Yes, there is intention because I chose to use the same song in hopes of creating a bell to ring. In this way it is better because, well something similar to fate.