In an old game, I played an Explorator by the name of 'Hadden Torian'. This character, through his adventures, became ever so slightly insane (cough); through his exposure to the warp, conversing with a (somehow) sentient ex-Psyker Servo Skull, and psychic adventures that his binary-logic mind failed to comprehend. It got to the point where he considered committing Tech-Heresy by converting the skull of a Kroot bodyguard into a Servo Skull.
The game has been re-born, everyone is creating new characters, and I was given the opportunity to re-create Hadden. He is now one of the 'Mind Cleansed', with all the bells and whistles - failsafe controls, eroding sanity, and the aptly named 'Shards of Memory'. All-in-all fairly fitting for a lobotomized Tech-Priest verging on Tech-Heresy.
How much of an effect do these 'Shards of Memory' have on the character? I would assume it'd be primarily up to the GM, but is there any specific set of rules that define when/what effect this has on the character (Eg. on a failed sanity check, you have to roll another sanity check or gain (x) sanity points)? Or is it just a bit of backstory that changes how the character might function in the world (Eg. triggers determined by the GM create episodes that the affected has to deal with; mini psychotic episodes)?