The article mentioned that after 5 yes-or-no questions in 60 minutes, the patients became exhausted. I'm guessing that activating certain parts of the brain requires considerably more effort for them than for a healthy person based on that.
The areas in question are areas tied to physical activity. They've been lying in a bed for a decade. It's not surprising that activating areas tied to physical activities is difficult.
I'm curious if the same fatigue would be present if the Yes/No responses were tied to critical thinking activities (though those are obviously more ambiguous to detect).
As someone with a traumatic brain injury from over two years ago that stI'll had cognitive problems on a daily basis preventing me from a range of tasks such as working in IT (careel of 10+ years) to (depending on the day) understanding the question "are you hungry?": i get mentally fatigued from answering questions, both critical and non critical thinking. Both are taxing and after less than an hour of ~15 questions I am unable to proceed or comprehend the information. The best analog I could give is when you wake up groggy and turn on a tv show that is in a language you don't know. Your brain is trying and searching but there are no connections being made and you only are aware that you are struggling but can do anything about it besides rest and give your brain time to recouperate.