What is the neurobiological basis of the "inner voice" used for thought or reading? I've recently experienced a number of hypnogogic near sleep states characterized by change in thinking (stage 1-2 sleep). I noticed that if I let go and get absorbed in the state, I can follow it.

I can describe the hypnogogic sensation as a feeling of empty space without a definite boundary. Typically the state arises at 17-23 minutes after bedtime (I'm using a timer to check). However, as soon as I activate "inner voice" or think a thought spoken in that voice, those other near sleep states get completely suppressed. Literally, a single word disrupts these states.

This makes me interested what happens in the brain when a person thinks using a single threaded, spoken train of thought? ("I'm typing a question on cogsci right now" or "I'm reading a question right now") Is there some part of the brain that gets activated while others get suppressed? In particular I'm interested why spoken thought suppresses other non-verbal states that a brain can consciously experience?


  Internal monologue, also known as inner voice, internal speech, or
  verbal stream of consciousness is thinking in words. It also refers to
  the semi-constant internal monologue one has with oneself at a
  conscious or semi-conscious level.


It would be interesting to know if there's some difference that fMRI can show between a brain that's reading using voice and brain that's reading non-verbally. 

I recall reading about similar phenomenon in the eastern spiritual traditions, like Taoism or Buddhism, where the states of mind they are trying to achieve are also incompatible with inner voice.
Preliminary answer I intend to improve later. Stumbled upon this in the context of description of how people read:

According to this paper on readin (Sousa, 2005), novice readers internally verbalize written words of English and German using "an area of the brain just above and behind Wernicke's area". This area then communicates with the Broca's area and the frontal lobe.

Found this additional article which mentions that people use the same area of the brain when reading silently as when listening actively.