In Cotard's Delusion, say some experts, the inner voice gets switched off. The little stream of subvocal speech that keeps talking to you as you do things. The one that says, I don't know why I am doing this, It's the inner consciousness that maintains the illusion that there's someone at home. If a stroke or a tumor inhibits whichever part of the brain controls this, then only the transient thought saying, this is what I am doing, exists. There is no background commentary. The coupling between thought and feeling about the thought is lost. In a sense, cogito ergo sum is lost. Instead, it becomes I do not think, therefore I am not. The clinical syndrome manifests as a person who believes he is actually dead. That inner voice seems to control the sense of feeling and reality as a person.

Now to change tack slightly, the whole point of writing--a novel, a poem, a letter--is to take charge of the voice in someone else's head for a short period of time.

This is what I'm doing now. My words are taking possession of the language circuits of your brain and I am transiently your inner voice.  In a way, that means I have become you, or you me, for a few minutes. The action of reading my words blurs the boundaries of reality. Writing is primitive virtual reality.