Michael J. Fox defends his advocacy against Rush Limbaugh’s ignoble attack: “Because the thing about … being symptomatic is that it’s not comfortable. No one wants to be symptomatic; it’s like being hit with a hammer.”

His body visibly wracked by tremors, Fox appears in a political ad touting Missouri Democratic Senate candidate Claire McCaskill’s stance in favor of embryonic stem cell research. That prompted Limbaugh to speculate that Fox was “either off his medication or acting.”

Fox told Couric, “At this point now, if I didn’t take medication I wouldn’t be able to speak.”

He said he appeared in the ad only to advance his cause, and that “disease is a non-partisan problem that requires a bipartisan solution.”

“I don’t really care about politics,” Fox added. “We want to appeal to voters to elect the people that are going to give us a margin, so we can’t be vetoed again.”

The irony is that I was too medicated. I was dyskinesic,” Fox told Couric. “Because the thing about … being symptomatic is that it’s not comfortable. No one wants to be symptomatic; it’s like being hit with a hammer.”