We could understand the human mind as a processor of information and the human body as a processor of energy. Of course are both parts intertwined and connected and much more complicated than we need for the reasoning here. The important thing is that the mind works with information and the body with energy. External information and external energy.
Both things are not part of any given person. The connection to the world beyond our skin is obvious: we eat, drink, breath, bleed, touch … we listen, watch, smell, feel… over a certain time all these sensations sum up to form a personality that is valid at a given time and within a given context. This restriction of validity is because all the sensations were made in a certain context and are therefore bound to this context. A change of the context might add new signals and alternate the personality.
Nobody can be completely disonnected from a context. Even in an empty room we have the room around us and the feeling in us. To derive somebody of his complete sensual sensations would have a severe impact on his state of health.
Everybody acts within a given framwork of relations and personality is often affiliated with the mind. So we might take the mind in closer consideration.
To approach the topic from a different angle: What makes a personality? We might say: The parents, the education, the culture, the food, the environment… and some more. The parents deliver a certain genepool but also education and training and socialization. Somehow the same but on a different level does the enviroment and the culture. Our behavior is defined by many constraints we have no influence on.
Still… there is a mind behind the skull. This mind processes information and evaluates situations and comes up with decisions. But all this is based on external input. This input might happen just on time, for example during a dialogue, or long-term via education or experience. And some thing do not even need to be learned as they are already part of the basic pattern of behaviour defined by the genes.
So… there is no such thing a individuality or individual responsibility. It is more a vast network of brains and knowledge transferred via the means of communication and evaluation. Objects communicate as soon as a person evaluates a given scenario based on previous experience. This experience again did not grow in the brain but was gained through behaviour within a given context.
The solace of all this is, that we can’t get lost without leaving traces. Our mind is part of a bigger context and while some ideas a preserved via the mind, the idea might preserve some traces of a single persons mind.