Giving a Voice to Autism

The main argument in favor of realistic novels, aside from the pleasure in reading them, is that they instruct us. By recognizing ourselves in fictional characters sent slaloming through the moral and ethical gates of life, we find our own repertoire of choices widened at those crucial moments when we, too, have to figure out what to do when a parent dies, a spouse deserts us, or the pilot gets on the PA system and advises us all to pray.
But what if a story is told by a man whose disabilities make it difficult for him to express his thoughts? My first novel was recounted in the third person and described, with fair autobiographical fidelity, my growing up with an autistic brother. I'm currently writing a novel told entirely from that autistic brother's point of view, and I find myself continually shoved up against a paradox: How do you make interesting a world which is by definition pathologically self-enclosed? How does the tool kit of the novel, with its venerable elements of dialogue, landscape and plotting, persuasively present the first-person experience of someone who is overstimulated by the input of life and yet lacks the cognitive means to process and communicate it?