I've been feeling a bit burnt-out on the subject of narcissism of late. I get tired of thinking about these twisted monsters, but I never fail to check out what Kathy Krajco is saying on the subject since she always has excellent insights to share.
I'd like to direct you to her blog post on how the narcissist permanently damages his/her brain by their believing falsehoods and twisting logic.
I have observed and wondered if narcissist's bring on their own dementia in their twilight years by how they've misused their minds. My musings on this began about half a dozen years ago when I started paying attention to aging narcissists. Kathy has provided a profound argument that is logically cohesive and I think proves that, yes, you can mind-f*** your brain to oblivion.