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 human papillomavirus vaccine.

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 bioethicist 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.