I do not think it dulls memory, but I'm not a MD, I do know my brother who has been on this stuff for over 30 years, has a great memory. Meds can affect people differently, so there are some that may have dulled memories, with this med or other meds.
As we get older, it's not unnatural to remember less, or it can happen when our heads are so full of thinking of multiple stuff, that perhaps, we temporarily run out of memory space.
It's an excellent med., I had been on Lithobid, but switched to Lamictal, for that seemed to address my depressive side much effectively. Other than that, it was great, I did much better with Lithobid than Depakote, switching over to Lithobid was the best thing for me, other than the Lamictal I've been on for a few years.
I have heard Topamax and the Benzo's, such as Ativan, to think of one at the moment, can dull memory.
It's always good to check with your doc/pdoc. when there is a concern, cause sometimes there may be some underlying physical condition behind this, best to rule out anything, than to wonder. Wondering, can lead to unecessary (sp?) worry, fueling anxiety.
Check it out, and please take care.