I would have read this about 20-25 years ago. I believe the subject was an alien individual, but it could have been a non-standard human instead.
The hook of the story was that the subject lacked an organ like the Corpus Callosum that allows the halves of the brain to communicate efficiently, allowing the illusion of a single consciousness. The subject is conscious, and has thoughts, but is subject to hearing commands like "Wash your hands!" "Fetch water!" within its head.
I recall the subject (and others like the subject) believing that the voices are their gods talking to them. To the reader it becomes clear that this is a separate part of the subject's own mind that is responsible for long-term planning and simply can't communicate with the rest of the mind in the way a "normal" human is accustomed to.