It's an interesting theory, but I'm not sure it really explains anything. E.g. that parts of the brain grow with use is certainly a surprising and interesting r

It's an interesting theory, but I'm not sure it really explains anything. E.g. that parts of the brain grow with use is certainly a surprising and interesting result. But it's not different than muscles growing with use, I don't think it requires agency to explain. Split personality is interesting, but also incredibly rare and may not really exist at all. Schizophrenia appears to be the result of physical damage to brain tissue, not merely healthy brains developing independent agents. Addiction is easily explainable with reinforcement learning gone wrong. There are theories of neural learning algorithms that are agency. Like the bucket brigade algorithm. But as far as I know that never worked very well. It's difficult or impossible to determine the "reward" for neurons, and having them be agenty doesn't really help anything.