That inner movie is not soft fantasy; it is a controlled hallucination running on hard sensory hardware. Visual cortex, auditory cortex and association areas fire in patterns close to those seen during real perception, so colors, voices and movement feel almost shareable with the outside world.
Yet the system is rigged against full-body takeover. Motor cortex still participates, but its output is downregulated by basal ganglia and prefrontal control, which act like a gate that keeps corticospinal tracts from driving large muscle groups. Tiny eye twitches or facial micro-movements may leak through, but the main motor stream stays throttled.
The sharper claim is this: the brain wants vivid simulation more than literal accuracy. Internal models in the posterior parietal cortex and the body schema in somatosensory regions are updated as if action were unfolding, while corollary discharge and efference copy signals flag these events as offline, preventing full autonomic and skeletal engagement.
Paradoxically, the more immersive the scene, the tighter the safety rails. Sleep paralysis, lucid dreaming and certain seizure states show what happens when the gating between imagery and action slips, with motor commands leaking into muscles or, conversely, being fully locked despite intense internal drama. The default setting keeps the movie bright and the body mostly still.
