I think you may have misread steenkh's post, I took it as them pointing out that damage to the brain has been shown to cause personality changes...
That works too.
I got thinking in terms of a differential scenario where the brain works as shown medically in one mode and then would purportedly operate differently when the proposed spirit is driving. There's no reason to suppose you couldn't measure that. I guess that's not really relevant.
I agree that when physical damage to the brain occurs such as the result of injury or disease, a personality change is often manifest and that this supports better a hypothesis that the brain itself is the seat of personality rather than simply being a conduit for some external entity.
I am currently caring for my mother who is now in late-stage dementia.
Caring for someone with dementia is exhausting. Caring for a loved one with dementia is an emotional disaster.
The various physiological causes of dementia (e.g., Alzheimer's disease) cause the various areas of the brain to operate out of synch, and thus to miss messages.
The deeper point is that we become
very attached to and observant of others' personalities. They can shape, dominate, enrich, and enrage our lives. Many shelves of books have been written on how we think personalities behave. It's very difficult to remember that our best objective evidence is that all this is just an emergent property of a kilogram or so of water, protein, fat, and a delicate balance of electrochemical reactions that can go off kilter at the drop of a hat. That emergent behavior is amazingly important the human experience, therefore it's intuitive to want to say it comes from something more profound than just an organ.
But then when faced with even a slight misbehavior of the physical organ, that illusion comes crashing down. When nature treats the brain as a protein and fat deposit, and attacks it with such mundane weapons as lesions and voids, there's no overlordly spirit to rise above it. Even small changes in the chemical or electrical behavior track with changes in personality and cognitive ability. The brain is remarkably resilient, but there's no magical preservation of the personality that suggests it lives somewhere else.
So if my tone gets a little mean in this thread, now you know why.
Indeed, this isn't a game for some people. No need to apologize.