With a undeniable amounts of evidence to prove the once 'theory'.

In schizophrenia, "hearing voices" (auditory hallucinations) is often a misattribution of one's own internal thoughts, which the brain fails to recognize as self-generated, causing them to sound like external speech from another person, according to recent brainwave studies. This disruption in the brain's self-monitoring system (corollary discharge) makes internal monologue feel like external voices, activating auditory regions as if real sounds were occurring. While normal inner speech is private, these voices feel real and can be negative, critical, or even commanding, but they are fundamentally a malfunction of thought processing, not perception. Bibliography - Google Ai.