Republican presidential candidate Rep. Michele Bachmann , R-Minn., waves as she arrives for a Republican Presidential debate Monday, Sept. 12, 2011, in Tampa, Fla. (AP Photo/Chris O'Meara)

(AP) -- A prominent bioethicist has offered $10,000 to charity if Republican presidential candidate Michele Bachmann can prove her claim that a vaccination caused mental retardation.

Arthur Caplan of the University of Pennsylvania challenged Bachmann on Thursday over her comments regarding the .

The topic of HPV inoculation came up Monday during a GOP debate. Afterward, Bachmann linked the vaccine to retardation, a claim vehemently disputed by medical experts.

Caplan says if Bachmann can identify a verified vaccine victim in one week, he will donate $10,000 to a charity of her choice. If not, Caplan says Bachmann should donate $10,000 to a pro-vaccine group.

University of Minnesota Steven Miles made a similar offer for $1,000.

Caplan says Bachmann hasn't responded. Her campaign spokeswoman didn't immediately return a request for comment.