It could affect consciousness directly.

I'm not sure how this argument works with the idea that a spirit lacks mass, energy, or physical presence. You would need to be able exert some type of influence on the electrical or chemical signals in the brain to create a perception of any sort, yet saying a spirit is non-physical removes any possibility of interaction with anything in the physical world, it would be undetectable by brains or equipment of any sort. It seems these ideas are incompatible. If spirits exists and are detectable in any way, they must have a way of interacting with the physical world