In Prisoner of Azkaban, Lupin states that:
‘Oh, no,’ said Lupin. ‘Much worse than that. You can exist without your soul, you know, as long as your brain and heart are still working. But you’ll have no sense of self any more, no memory, no ... anything. There’s no chance at all of recovery. You’ll just – exist. As an empty shell. And your soul is gone for ever ... lost.’
And in Order of the Phoenix, Severus Snape says:
“Only Muggles talk of ‘mind reading.’ The mind is not a book, to be opened at will and examined at leisure. Thoughts are not etched on the inside of skulls, to be perused by any invader. The mind is a complex and many-layered thing, Potter . . . or at least, most minds are. . . .” He smirked. “It is true, however, that those who have mastered Legilimency are able, under certain conditions, to delve into the minds of their victims and to interpret their findings correctly. The Dark Lord, for instance, almost always knows when somebody is lying to him. Only those skilled at Occlumency are able to shut down those feelings and memories that contradict the lie, and so utter falsehoods in his presence without detection.”
Also, Harry Potter housing a piece of Lord Voldemort's soul allows Voldemort an Harry to look into each other's minds when both are at their relaxed moments and intervals. They see and share each other's thoughts unless at least one or the other blocks it off with Occlumency.
So if thoughts are not etched into the mind, are they etched into the soul?