How the brain produces internal speech
Top-down (prediction) connections
The brain uses predictions in perception all the time. Our sensory perception is a mix of actual external input with the predicted input. We perceive them both. Here’s a nice TED talk about it.
The Basal Ganglia (“Break pedal”)
The Basal Ganglia is a brain region that can inhibit our muscles — all of them — by controlling the brain region that is the final stop before the spinal cord (Motor cortex 1, M1).
The Prefronal cortex (“Will”)
The prefrontal cortex is the abstract upstream of M1 — It’s the area that represent abstract “will” and desires that later translate to actual muscle movement via M1.
Internal speech is produced when “speak” command is sent from the Prefronal cortex to M1 while simultaneously applying the breaks (using the Basal Ganglia).
The prediction model predicts that the “speak” command will result in hearing that speech. The top down connections make us perceive this prediction as actual speech sounds.