That right-brain/left-brain thingy is true. I find that after I have been totally engrossed in painting for a few hours and then try to immediately write about what I have been doing, it is more difficult that if I wait for about an hour and get the left side of my brain a chance wake up. This explains why some of my blogs can be a little disjointed but I do try to go back and edit them if when I read them later they confuse even me.
I have learned to talk while I paint. When I teach and give demos it is necessary. But I find I need to either have a rough idea of what I want to explain in my head before I start painting for it to work, or to work on something very familiar to me that I can paint it without thinking too hard. My palm trees are a subject I can do that with.
It is a very interesting phenomena when you actually experience it. Sometimes you don't notice it but when you do it is kinda funky.