I haven't run for the Webster's yet, but I suppose it depends on if you're considering "brain" as strictly being the cerebral cortex. It's what most people think of when they think brains, the grey matter. But I also think that the bits attached to it are all part of it, including the nerves, hypothalimus, pituitary gland, etc. All that together is the "brain".
What I've been tellng people to ease them into it is that I have an overgrowth of cells on the nerve that is in charge of hearing/balance. Depending on who the person is, I may go into it more than that. Or they may ask me. At first, I was trying to be real careful because it bothered me to say something that obviously made them uncomfortable, but at some point realized that I didn't want to feel any more uncomfortable than I already do. I find if I distract most people with technical details, and make it sound like an interesting thing to study, most people walk down that "fascinating" path with me, and are put at ease. This just comes with the level of comfort I feel in my research about what I have. Amazing what one can learn in a few short weeks.
Having the ANA booklets around for anyone that is really that interested in me has been helpful as well.