my memory pieces tell me to shut up too when I am in therapy. The way I handle this is by putting all my attention on my therapist - what she is saying, what she's wearing, what the room looks like, what the chair or couch I am sitting on feels like and remind myself that it's just a memory and I continue talking, after a few minutes of grounding myself and staying aware that I am experiencing a memory and its not really happening (my abuser is dead and not in the room with us) it goes away. At first I couldnt do this but each time it happened my therapist and I kept trying to go just one step or question further each time until now I can do this.

addition to post-
I just went to my blog because I remembered writing about this very thing yesterday. So you can find more information there on my experience with this.

Also to those having trouble with losing blog entries as they type them or when they click on blog this -

if I type in only a few sentences and then click blog this then go back to typing the whole blog entry by using the editing feature I don't lose my entries. This has saved me alot of retyping.