Brie Larson is opening up about what inspired her tour de force performance in Room .

In the film, Larson plays Ma, a young woman held captive with her five-year-old son, Jack, in a garden shed. The actress underwent six months of intense preparation for the part, studying the effects of everything from sexual abuse to vitamin deficiencies. She even stayed out of the sun for months and worked out with a trainer until she had achieved just %12 body fat.

But what allowed her to embody the character more than anything was the realization that her own childhood bared some resemblance to the emotional hardships Ma and Jack endure in the film.

“I always wondered why I knew this story so well,” she tells Variety in her cover story. “It wasn’t until then that I realized there was another piece of me coming out from this story, and I got to live the experience of being my mother in that situation,” she says.

When Larson was around 7, she travelled to Los Angeles with her mother and younger sister, Milaine, in hopes of becoming an actress. Larson thought the trip was only supposed to last a few weeks, but later learned that her parents had divorced, and the studio apartment her mother had rented became their permanent home.

“It was Room ,” Larson says she came to realize. “It was all one room; the bed came out of the wall. I had two pairs of jeans, a couple shirts, a couple headbands and a pair of orange Converse (sneakers).”

RELATED: How Do Celebs Plan to Unwind After Awards Season?

Just like her character in the film, the actress says, “My mom created this amazing world, and I never remembered it as being a time where things were tight, and we were just eating Top Ramen and 99 Jack in the Box tacos, and I didn’t have any toys. It didn t feel that way to me at all; it didn t feel sparse.”

While her mom stayed strong for her kids, Larson does remember the night she learned how bad the situation really was. “She was holding her hand over her mouth, trying not to wake us up with these guttural sobs. And I thought, ‘That reminds me of when my toys are taken away,’ ” she says.

“It wasn t until much later I realized, ‘Gosh, we never went back to Sacramento. I never saw my dad.’ Years later, I realized that right before we had left for what was supposed to be a three-week thing, my dad said he wanted a divorce.”

During her preparation for the film, Larson says, “I was constantly going through these waves of forgiveness for myself, waves of forgiveness for her. I would call her, crying and apologizing for everything I didn t understand and didn t know.”

Room won the People’s Choice Award at the Toronto International Film Festival, and talk of an Oscar Larson’s performance is already buzzing.