What seems to be happening is that there is a network in the brain that is responsible for internal awareness, awareness of our own body, awareness of our emotions, awareness of our self-related thoughts, and in Cotard's, it seems like that particular network is tamped down. In some sense, their own experience of their body, in all its vividness, in experience of their own emotions in all its vividness, that's compromised very severely. In some sense they're not feeling themselves vividly. It's as simple as that. But, then there's something else that's happening in the brain. It seems like parts of the brain that are responsible for rational thought are also damaged. First of all, what might be happening is a perception that arises in their brain saying that they are dead because they're not literally perceiving their own body and body states and emotions vividly and then that perception — irrational though it is — is not being shot down. - www.npr.org