I've recently watched The Theory of Everything and it got me thinking. How does a researcher with a serious physical impediment, such as Stephen Hawking, conduct his research?

Academic life usually involves studying, staying up to date with current literature, attending or giving conferences, teaching some classes, etc. Each of those activities presents serious challenges. For instance, how does he do math? Everything is done in his mind or does he scribble some notes on software? Or maybe in Latex? I'm assuming he has people helping him, too.

I'm not sure if this is on topic here, so I apologize if it's inappropriate.