Rand decided that the memories/skills came from memories of his past life as a result of effects of the taint, but that the personality of Lews Therin talking to him and having a voice and will of his own was a construct of his mind, ie: like schizophrenia.

He may be right, he may be wrong. It's something we know will never be resolved. RJ had his own answer and it's in his notes, but Brandon said RJ specified this matter should remain open to each reader's interpretation. "The seeping memories and the fear of being LTT reborn made Rand go insane and create the voice as a schizophrenic construct to cope" doesn't appeal to many readers ( a lot of people are really incomfortable with the idea that Rand was going insane), and "The real LTT was talking to Rand" doesn't work with others for the opposite reasons - and there are those who stand in between and think LTT's voice was real but its presence was driving Rand insane, that the cause was entirely different but the effects were very similar to suffering from schizophrenia. Rand being the central character and much of the story being driven from his POV, it's probably clever of Jordan not to impose a final answer on the reader about Rand's insanity.