 Hypnotic regression to retrieve memories has now been shown to be largely the product of imagination, that memory is not like a recording device in the brain in which you rewind the tape and play it back on the Cartesian theater of your mind and the little homunculus in there is watching the screen and reporting to some other part of your brain what it's seeing happen. There's nothing like that. The moment you ask people to reconstruct a memory of what happened, they start to change it.