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ABC News' Arlette Saenz and Ali Weinberg report:

Actor Seth Rogen is best known for his role as a pot-smoking jokester in comedic hits like "Knocked Up" and "Pineapple Express," but he joined the ranks today of other celebrities who have brought their Hollywood star power to Capitol Hill.

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"Thank you for the opportunity to testify today, and for the opportunity for me to be called an 'expert' at something, because it makes me feel smart," Rogen, a celebrity champion for the Alzheimer's Association, said before a Senate Appropriations subcommittee.

"I should first answer a question I assume many of you are asking: Yes, I'm aware this has nothing to do with the legalization of marijuana. In fact, if you can believe it, this concerns something that I find even more important."

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The 31-year-old actor's personal experience with the disease (his mother-in-law suffers from it) was what brought him before the Senate panel today. And Rogen wasn't the only star in Washington. Actor, director and Oscar-winning screenwriter Ben Affleck testified before the Senate Foreign Relations Committee on the prospects of peace in the Democratic Republic of the Congo.

Does that make Affleck an expert on the issue?

It depends on whom you ask. He is the founder of the Eastern Congo Initiative, which writes grants to local community leaders and does advocacy work, but notably his offer to speak before a partner House committee was turned down.

A Republican aide on the House Foreign Affairs Committee was quoted by Foreign Policy as saying, "people serious about resolving problems … want to have serious conversations with experts and leaders in the field, not celebrities."

Even Affleck, who has taken multiple trips to the war-torn nation, has acknowledged that while he cares about the people there, he's not the world's top Congo brain.

"I'm not any kind of ambassador, I'm not going to give you a history lesson," he said in a 2008 report he filed for ABC News' "Nightline."

"Among other reasons, I wouldn't be qualified. I simply want to share what I've seen."

(Charles Dharapak/AP Photo)

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Rogen, along with wife Lauren Miller, founded Hilarity for Charity, an advocacy group that raises money and awareness for Alzheimer's disease. Rogen and Miller became active in the Alzheimer's community after Miller's mother was diagnosed with the disease at the age of 55. Miller's grandparents also died of the disease.

"I've personally seen the massive amount of financial strain this disease causes, and if the American people ever decide to reject genitalia driven comedy, I would no longer be able to afford it," Rogen said in his testimony today. "Therefore, I can't begin to imagine how people with more limited incomes are dealing with this."

Rogen said he wanted to share his story "to show people they're not alone."

"Americans whisper the word Alzheimer's because their government whispers the word Alzheimer's. And although a whisper is better than the silence that the Alzheimer's community has been facing for decades, it's still not enough," Rogen told the committee. "It needs to be yelled and screamed to the point that it finally gets the attention and the funding it deserves and needs, if for no other reason than to get some peace and quiet."

One Senate Democratic aide emphasized that Rogen's "story on Alzheimer's is very relevant because his wife's family is an example of genetic Alzheimer's disease. There is a very real issue of likely carriers deciding whether or not to get tested, if there is no treatment available."

Affleck and Rogen are far from the only movie stars who have used their celebrity status to raise awareness of the issues they care about. Actor George Clooney testified in 2012 about the ongoing civil war in Sudan, and also had a private visit with President Obama. Actress Ashley Judd has urged Congress to develop a vaccine for HIV and to provide funding to help protect America's wildlife and natural resources.

In 2000, Lars Ulrich, a drummer for Metallica, testified before Congress about copyright infringement and racketeering. Former "Price Is Right" host Bob Barker took to Capitol Hill to tout the importance of neutering pets. Even "Sesame Street's" Elmo has taken a star turn in Congress (the Muppet advocated for more funding for music programs in schools).

And there have been times when a celebrity's testimony on Capitol Hill turned completely comedic too, as when Stephen Colbert submitted serious testimony to a Senate panel about immigration overhaul but then quickly turned into his late-night show character.

"This is America," he told lawmakers. "I don't want a tomato picked by a Mexican. We do not want immigrants doing this labor."

(Bill Clark/Roll Call/Getty Images)