I couldn't tell you about neuropathways, but I asked the person I spend the most time conversing with if she thinks I'm stupider than before. She says I'm not so much less intelligent as more A.D.D. and less interested in "intellectual stuff", but she doesn't think it's due to lack of ability. She says that you can only spend so much time on your various interests, and now that I spend more time on my hair and stuff I have less time for more intellectual pursuits.
To be fair, she hates anyone spending time and effort on their hair or nails or anything beyond the absolute bare minimum of grooming :p
I admit I do feel a bit dumber at times, it seems like I make more absent minded mistakes. I'm more flighty and somewhat less inclined to sit and think deeply about a subject, but way more inclined to sit and
feel deeply about a subject. It seems like I still have the capability to draw on, but it's boring and I'm too busy chasing emotional highs to be coldly analytical about everything that passes through my brain.
That's not -necessarily- an HRT thing, it could just be the fact that I'm not emotionally dissociated anymore and am kind of OD'ing on emotions. Wheeee!

Edit : She's the smartest person I know and she expounded further : She says any time you do stuff like changing the hormones present in the brain so it rewires you're going to have some intelligence changes. Either becoming more or less intelligent or even both at the same time.
We both kind of think my brain has re-plasticized a bit and I'm gaining understanding and knowledge at a faster rate than previously, but my areas of excellence and interest have changed a bit. Just one example, spatial reasoning - I've had multiple people make fun of my parking jobs since spring. I've always been an excellent driver - this is the first time anybody's ever been able to tease me about anything regarding driving or parking, but for a few months there I COULD NOT park perfectly parallel to the lines to save my butt. It was hugely frustrating. I'd get it all lined up, park perfectly, get out and be like |\|
>:/