>And I can't prove it either way.

Not true. This is "provable" aspects of you and your personality can be changed by physical changes to the brain. There are thousands of instances of this including experiments that verify this.

While you can't "prove" this simply by observing this phenomenon among other people that level of "proof" is impossible. You technically can't prove anything and what we see with physical changes to the brain visibly influencing personality and behavior meets a reasonable criterion without getting too pedantic.