HOLLYWOOD — Michael Shannon is a big, imposing guy (whose head may weigh a whopping 15 pounds if one is to believe Internet biographies) who has played a lot of intense, imposing characters in such films as "Bug," "Before the Devil Knows You're Dead" and "Shotgun Stories." In "Revolutionary Road," Sam Mendes' film about 1950s angst, Shannon cranks up the intensity to almost uncomfortable levels.

The film reunites "Titanic" stars Kate Winslet and Leonardo DiCaprio as April and Frank Wheeler, a married suburban couple who seek to break free of their staid existence. As John Givings, a brilliant mathematician who suffered a mental breakdown, Shannon has two pivotal scenes with the couple, scenes in which his brutal honesty cuts to the very core of their disintegrating relationship.

Q. I never knew the 1950s were so traumatic until I saw "Revolutionary Road."

A. It was an era of containment, it seems to me. People were trying to keep it all together and keep it inside. My dad, when I talk to him about that era, he was kind of wrestling with some of that, too.

Q. What did your father do?

A. He was at undergraduate school at the time. He was going to Duke and studying French literature and philosophy. He is a real intellectual, bohemian guy. One day he just decided he couldn't handle thinking about all of this stuff anymore, and he switched over to accounting.

It's a real parallel with this environment, this atmosphere that is created in the movie of grappling with these impulses to want to be a citizen of the world and have a really deep and fulfilling intellectual and spiritual life, and on the other hand being stuck in this era.

Q. Does Richard Yates give John Givings a back story in the novel the film is based on?

A. There wasn't a huge amount of history given in the novel. He talks about the fact John was out West and he was a professor of mathematics. He had a breakdown and came home, and his poor mother was trying to take care of him. Basically, he wanted to kill her and blamed her for all of his problems.

There are some clues, I think, in just kind of a superficial way. He is an only child, which is a bizarre journey, particularly if you have parents like that. I am assuming he probably wasn't very athletic or he probably wasn't very popular in school and just got sucked up in this life of the mind. ... He has gone so far in this thinking, and it's driven him mad.

Q. Did you do research on the effects of shock treatments?

A. I had a hard time finding anybody to talk to about it, but I did read about it, and I had read even before other accounts of people who had gone through shock treatments. One of my favorite musicians is Lou Reed, and I had read his biography where he had been subjected to numerous shock treatments. Actually, the song of his "White Light, White Heat" is kind of an ode to his experiences with that.

Q. John says he's had some 30 treatments.

A. I think it's something we can all identify with in terms of the loss of control about what happens. When you find yourself in the situation where other people are deciding what's best for you — your ability to make decisions for yourself gets revoked. That is one of the most horrifying things that anybody can imagine and live through. He also seems to have found, at a certain point, a warped acceptance of it — "This is what's happening to me, and there is nothing much I can do about it. I am just going to make sure I punish as many people as possible."

Q. John really serves as a bookend to April and Frank's story.

A. He really is important to the story. It's a hard movie to describe to people when they ask you what it's about. But if you boil it down to its essence, it's about these two people — Frank and April — trying to make a decision: Do we stay here and suffer silently or do we try to liberate ourselves and escape to a better life?

The first time we see John they are celebrating their decision and reveling in this newfound sense of freedom. John is there to kind of celebrate and validate their decision. Then John comes back, and this freedom has crumbled, and he's there to castigate and punish them for their loss of faith. I think that's the really beautiful thing about the character.