A couple I know have been married decades. She now has Alzheimer's and is in a wheelchair. He attends her 24/7, feeding, cleaning and dressing her. She is completely incapable of communication but is alert and her eyes will follow your movement when talking to her. I sometimes wonder if he has sex with her if that would be considered rape since in Canada there is precedent of being charged with rape if your wife has not given consent to having sex.