a. High intensity inner monologue (in some cases dialogue) that distracts or interrupts activities in the external world.
b. Source of artistic inspiration; often brilliant, sometimes hard to keep pace with.
c. Stuff going on in your head that suggests you should maybe get a second opinion (other than yourself) about your mental well-being.
x: Um, so would that be a yes or a no?
y: Oh, did you say something? Brain chatter going high volume there. Sorry. What was the question?
x: Will you marry me?
y: Oooo – hey, can I get back to you on that? It's really busy in here right now and I'm missing part of what they're saying.