'Zero Dark Thirty' Star Jessica Chastain on Her Emotional 'Straitjacket' During Torture Scenes (Video)

"During those scenes, anything I felt -- it was like wearing a straitjacket," the actress tells THR. "I had to have a buffer."

When Jessica Chastain was playing a real-life CIA agent in Kathryn Bigelow’s Zero Dark Thirty, which traces the decade-long hunt for Osama bin Laden, she had to turn off a part of her personality to work through some of the film's toughest scenes.

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The film -- which has been received well by critics and on Wednesday received five Oscar nominations, including best picture and leading actress for Chastain -- features a significant amount of torture. The torture scenes have become the topic of heated debate after U.S. senators assailed the film for alleged factual inaccuracies regarding the torture.

Sens. Dianne Feinstein, D-Calif., Carl Levin, D-Mich., and John McCain, R-Ariz., have criticized the film because they believe it suggests that information obtained by torturing Al Qaeda detainees aided in the search for the terrorist leader.

When Chastain was shooting these scenes, she says she had to go against everything she has learned in her own life.

“I’m playing a character that’s been trained to be unemotional and analytically precise. My whole life, I’ve been trained to be emotional,” she says. “During those scenes, anything I felt -- it was like wearing a straitjacket. I had to have a buffer.”

However, in one scene in the film, Chastain’s character Maya expresses her frustrations in an angry rant to her boss (Kyle Chandler).

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“I thought when playing a character like that, there needs to be the moments where. when she does explode or have an emotion, there’s an extreme of it,” she says. “There’s something a little bit crazy about it, because she’s someone who's been closed up for so long.”

Chastain, who was not able to meet the CIA operative who her character is based on, says she “basically went to school” about three months before she started shooting the film, which opens wide on Jan. 11. She spent a lot of time speaking with Mark Boal, who wrote the screenplay for the contender film. She also read books, including The Looming Tower: Al-Qaeda and the Road to 9/11 and Michael Scheuer’s book Osama Bin Laden.

“I used my imagination to fill in the blanks of the research that I couldn’t do on the character,” Chastain says. “If you see the movie, you’ll see there’s a child’s drawing in Pakistan, there’s postcards, screensavers, American candy. All of those things I was trying to make reminders of the life that she was becoming a stranger to.”

Zero Dark Thirty opens wide on Jan. 11. Watch THR's interview with Chastain above.

Email: Rebecca.Ford@thr.com; Twitter: @Beccamford