You may be interested in a TED talk given by neuroscientist Mariano Sigman, in which he describes, not only how associative semantic analysis of speech and text can accurately predict future mental problems, but also how the same kind of analysis on ancient texts shows that concepts associated with introspection hardly appeared until around 500 years BC, when they increased dramatically (see 6':45" for a graph) :
Your Words May Predict Your Future Mental Health.
All of which provides surprising support for the suggestion that, until that time (the start of the Classical period of Ancient Greece), the ideas and thoughts that pop into the mind (joining the internal monologue) were generally interpreted, not as internally generated, but as the voices (comments, suggestions) of the spirits or gods; and the subsequent growth of rationalist natural philosophy led to an introspective reinterpretation based on the relation between conscious and subconscious mental processes.
This has a remarkable correspondence with the description of the origins of modern consciousness in the controversial theory of '
Bicameralism' - and your post suggested to me the possibility that many religious traditions and practices are aimed at reactivating this early dichotomous interpretation (so the celebrant hears parts of his internal monologue as the voices of spirits, angels, or god).
All pretty speculative, of course, but interesting speculation...