LRH
in the example you mentioned I would think that so many nerves woulod be damaged that the brain would be incapable of gathering enough information to continue as the old personaity.
Some research on people with Dissociative Identity Disorder (multiple personalities) has shown that when a particular personality is in charge the brain alters the wave patterns around that particular personality. There has been dispute about it but the assumption is that personailities are created while a person is in an altered state of awareness - a type of hypnosis that reaches many different levels. Each personality would exist on a different level of consciousness.
The theory is that normally infants and young children live with this type of disunified personality (which they believe helps us understand why babies can be crying one minute abd laughing the next. There is no free flow of information and personality yet. As the child ages the brain becomes more capable of cross-indexing information to create a well rounded person who is able to express a wide range of emotions and sometimes experience more than one at a time. (This theory might also exlain the cult-induced personality that can so totally disregard certain facts presented to the person). During normal development the person becomes aware of all the different parts of the self - a very complex human with a wide range of feelings, beliefs and behaviors. Abnormal development (such as that by a cult that controls information, thoughts, behaviors and feelings) would limit the individuals ability to access all the parts of the self.
Any physical brain trauma such as you describe might leave certain parts of the brain fully intact enabling the person to continue to function but if the rod went through the many feeling centers of the brain then those parts would no longer be accessible.