Fox Stem Cell Research

Actor Michael J. Fox says he's not bothered by criticism from radio talk-show host Rush Limbaugh.

Fox made the comment in an appearance on ABC's "This Week."

Limbaugh said on his program last week that Fox exaggerated the effects of his Parkinson's disease in a political campaign ad for Democrats backing stem-cell research.

Limbaugh said Fox's moving and shaking were "purely an act." Limbaugh later apologized.

Fox says the comments did upset others who have the disease, but says he doesn't react personally to attacks.

He says responding would be "like getting into a fight with a bully."

Fox says he's grateful to be in a position to "make a difference and do positive things."

The actor has been an activist for stem-cell research, which could lead to a cure for Parkinson's.