well i always thought if at this point his brain has been damaged by mako.. seeing at the point where he just got out of hojo's lab his brain was very vulnerable and thats how he took on another persons memories and believed it to be his own. having another personality wouldn't that make him sort of skitzo. and if so the voices in his head are another part of him in his subconcious, maybe the real him. btw when i say a different personality im referring to the badass he is in ff7 for ps1 is not the same in crisis core and his memories as a child... in each of the latter he is no where near a badass, he is very timid and shy..