Because they cannot correspond to anything else, by definition. Ask yourself, how do you know there was a Rand, an Aristotle, an Aquinas, a church or anything else? The problem here is you are ignoring the incalcuble learning curve you yourself went through from the moment of being born until you began thinking independently. How do YOU know there are chemicals in anybody's brain, let alone Rand's? It presupposes the very correspondence you question.
You see, you steal so many concepts here that it becomes impossible to see that these questions make absolutely no sense without the stolen concepts, which are all, unequivocably and without exception, based upon the very correspondence that you question, otherwise you wouldn't know about any such things to ask the question.
There is, then, the obvious problem of knowing that our impressions are true representations of reality. There is no way to check them that does not itself rely on sensation and so is open to the same possibility of error.
Once again, how is it you can make a distinction between 'true representations' of reality as opposed to 'error' without already having objective definitions within your own brain as to what these terms mean. In other words, why isn't your observation that we are subject to error, subject to the same error which would therefore prove that we cannot know we are subject to such error.
This whole line of reasoning negates itself.
If there were error, that was in fact, all pervasive and undetectable, then it would be invisible to us and irrelevant for all intents and purposes. And if it can be proven, objectively, that there is such error, the proof demonstrates that it isn't 'error' but faulty conceptualization which is corrected by other observation and more accurate conceptualization. There is no problem here.
Thank you.
Last time for everybody. Rand (and all materialists) have no logical, coherent, non-contradictory explanation for the trustworthiness of our senses.