Julian Jaynes’ 1976 book, The Origin of Consciousness in the Breakdown of the Bicameral mind, put forward the hypothesis of “the loss” (former existence) of a particular function one part of the brain, formerly had. Jaynes hypothesized a brain split in half, one half “speaking”, actively outwardly doing, and the second half receiving, as it were, “listening” and obeying. That in this lost way our brain formerly worked, lateralized into two halves, the one that received “messages”, would then send those messages to the other half of the brain to then act out those messages. Sound vaguely familiar? Yes, ‘hearing voices’, “the bicameral mind was experienced as a different, non conscious mental scheme wherein volition in the face of novel stimuli was mediated through linguistic control mechanism and experienced a auditory verbal hallucination”(Wiki).
But hang on, don’t jump off the wagon of Jaynes’ theory just yet, because it might have some weight when one thinks that before our secular age, hearing godly voices was a (normal) thing. “Rather than making conscious evaluations in a novel or unexpected ways situations, the person would hallucinate a voice or “god” giving admonitory advice or commands and obey without question. “(Wiki). “One would not be at all conscious of one’s own thought processes per se. “ (Wiki)