IOWA CITY, Iowa – Republican presidential candidate Newt Gingrich defended himself against attacks from his rivals on Wednesday when he ran into a sustained protest at what was supposed to be a low-key event about the human brain.

Gingrich, the former speaker of the U.S. House of Representatives, is trying to hang on to a lead in Iowa to score a victory in the state’s Jan. 3 caucuses, the first U.S. nominating contest in the Republican race to choose a 2012 presidential candidate.

But to do it he will have to overcome sustained negative ads and daily attacks from his rivals, such as a comment Mitt Romney made to The New York Times on Wednesday calling him “zany.”

Gingrich vowed to remain positive in a session with reporters and kept referring back to his proposal for a public-private partnership to accelerate ways to reverse Alzheimer’s.

Other campaigns can do what they want, “and I’m going to run the campaign the way I want to,” he said.