We have a local program called C.A.N.T.E.R. that puts both mentally and physically challenged youth as well as adults on horse-back and it helps.
My horse and I have been a team for almost 8 years, she knows what I want to do almost before I know myself, and I know what she's thinking. Unless she's in a stroppy mood all I have to do is shift my weight from one hip to the other. Jumping her is almost uncanny, she has a very adjustable stride and all I have to do is think "short" or "long" and she compensates.
It's exhilarating and tremendous fun, I'm sure it would do anybody good, and the feeling of freedom if you're physically or mentally handicapped has to be great.