In the last year or so, I”ve seen Keira Knightley withering away on a hospital bed as her inorganic organs are removed and farmed out, moodily chain-smoking in an icy Manhattan loft as she contemplates her husband”s infidelity, stridently slamming doors on a West End stage as her life is undone by malicious rumors about her sexuality, and most recently, getting the life spanked out of her by Carl Jung as he attempts to cure her of crippling hysteria.

It has, in short, been a rather intense time for Knightley in the fictional realm, so it”s a relief, not to mention an irrational surprise, when the young Londoner answers the phone with the perkiest of hellos. It swiftly becomes difficult to reconcile the fast-talking, warmly enthusiastic person on the line – the word “incredible” pops up with endearing frequency throughout our chat – with the prickly, often unhappy women she”s lately brought to life on screen (and, in a superb London revival of Lillian Hellman”s “The Children”s Hour” last spring, on stage too).

But that disjuncture is what makes Knightley among the most intriguingly self-testing major stars of her generation. Blessed with the face, physique and magnetism that have many of her female peers stuck in beige rom-com/action babe purgatory, Knightley has, since scoring an Oscar nomination for “Pride and Prejudice” at the tender age of 20, actively sought out a thornier path for herself.

“I took a year off to think about what I wanted to do and the direction I wanted to take things in, and those recent films and the stage work came out of that year,” she explains, acknowledging the stark tonal consistency of her recent work. “All those choices have been about pushing myself, trying to tackle things I don”t necessarily understand. This is going to sound really wanky, but any form of art is about trying to make sense of the world around you, and that”s what I really love about my job.”

Knightley”s cheerful admission that she doesn”t initially ‘get” every character she plays-indeed, that this lack of accessibility is a drawcard for her-is as winning as her schoolgirlish insertion of “wanky” into the conversation. Her inclination towards difficult and not especially commercial projects recently culminated in her trickiest, most prestigious outing to date: David Cronenberg”s cerebral Freud-Jung study “A Dangerous Method,” in which she plays the crucial (and, some might say, central) role of Sabina Spielrein, a former patient of Jung”s who overcome mental illness to become one of the first female psychoanalysts.

Knightley”s fondness for somewhat inscrutable female characters reaches its zenith with Sabina, and if her performance has both ardent admirers and unconvinced detractors, it”s certainly her most questioning and boldly realized characterization to date. “With a character like Sabina, I don”t necessarily understand her behavior, where she”s coming from,” she says. “So I have to find that empathy within myself, so I”m not judging her, I”m looking into her. I love doing that. It was the same with, say, ‘Never Let Me Go”: I was fascinated by that character because she”s a walking study of corruptive jealousy, which is an emotion I have difficulty relating to. The more of a challenge it is to understand a character, the more I want to play her.”

Thrilled as she was to be approached by Cronenberg-“I was 99% sure I would take it before I even knew what the script was,” she says breathlessly-the potent sexual content of Christopher Hampton”s script, more explicit in its sadomasochistic implication than actual flesh-baring, did give the actress cold feet early on.

“I was wowed by the script, but I phoned David up and told him I didn”t know if I could do it: with the world and the internet being what they are now, I wasn”t sure if I wanted that out there. And he said that was fine, we just wouldn”t shoot those scenes. Which I thought was wrong: those scenes are vital in understanding Sabina and her psychology, whether they were to be played by me or another actress. And the more we talked about it, the more confident I felt: David made it clear he didn”t want the sexual content to be titillating, he wanted it to be brutal and clinical. That made sense to me. I could do that.”

It”s not merely the sexual candor of the material that makes playing Sabina a tall order for a young actress; the outward manifestations of her hysteria are no less challenging. Knightley fearlessly takes on the violent out-of-body language and oral fixation that plagued Sabina at her most deranged: it”s a full-on approach that risks alienating audiences to some degree, and the actress relied on her director to keep her from going off the edge.

“When you”re making a film of this nature, particularly playing a hysteric, you need to really trust your director: in lesser hands, this material could be very tricky, and I don”t know if I would have gone as far as I did with the character,” she says. “In its exploration of the physicality, David”s work has always gone way beyond and out the other side of what any other director would do – but he also knows exactly when to hold back. On a film like this, it”s important to trust the director”s taste, and everybody on set implicitly trusted his.”

Cronenberg insisted they begin by shooting the therapy scenes between Sabina and Michael Fassbender”s Jung, where the character is at her most frenzied: this essentially threw the actress in at the deep end, but she believes it was the right decision. “Those scenes laid out exactly how far David wanted me to take it, so it was the best place to start,” she says. “I could totally push it out there, and then pull it back to a degree. And for the rest of the film, it was this kind of levelling-off process – pushing and pulling as required. Those therapy scenes had to be the most intense: if they”d been less than what they were, we wouldn”t have had enough room to retreat.”

Though the rest of the film traces her psychological recovery, it”s not all one-way emotional traffic from that point, she explains: “What”s interesting about Sabina is that, as incredible as her recovery was, it wasn”t a miracle cure. There wasn”t a button you could push: she was always living with her condition, it was her lifelong battle to keep it under control, to keep the well side dominant over the destructive side. So in all the later scenes, David and I were focused on how close she was to falling apart at that specific point, how much she”s trying to rein it in. So it was interesting playing someone for whom that degree of control varies from scene to scene.”

In locating the character”s physicality, Knightley looked to a number of sources – beginning, of course, with Hampton”s original play. “There”s a description in the stage directions that says her face is ‘ravaged by tics.” And I wondered what exactly that meant, so I asked Christopher, and he said, ‘It means whatever you like.”” She laughs. “So I went to David, and he said, ‘I definitely want it to be on the face, and I don”t want it to be funny.” Okay, anything else? ‘Nope.””

“So I read an awful lot, looking for more specific descriptions of what it might be, and there weren”t really any. So I zeroed in on a part of Sabina”s diary where she described herself as “a demonoid dog,” which is such a fucking awful way of seeing oneself, and reveals so much about her. So I took inspiration from that. I wanted something demonic and animalistic, to put her interior struggle into wild exterior behavior. I also looked at a lot of Francis Bacon paintings for ideas: one in particular called ‘Study for a Crucifixion.””

Amid the trawling of library books and art galleries, there was some time for silliness too: “Well, of course I spent a lot of time in front of the bathroom mirror, pulling faces at myself! Then I”d get on Skype with David and give him three options, and he”d pick one.” She lets forth a pleasingly throaty laugh; I”m not sure I”ll ever be able to watch Knightley”s severe jaw contortions in the film without thinking of her showing them off in a Skype window.

Does she ever feel like bringing some of that more playful side to the screen – to join her peers on the genre train? She hesitates, choosing her words carefully. “If I could find a rom-com project with a character as complicated in her own way as the women in the films I”ve been doing recently, I”d gladly go for it,” she says, her tone making it clear that such scripts aren”t exactly written by the dozen. “But I did do a comedy over the summer, because I thought, ‘Jesus, this is just going from dark to darker to darkest, I need to lighten up a bit.””

The film, an ensemble piece titled “Seeking a Friend for the End of the World,” stars Steve Carell, and she evidently had a good time doing it. “I told a friend, ‘Don”t worry, it”s much lighter,” and then when she asked me what it”s about, I had to say, well, the end of the world!” She smiles audibly. “Maybe the apocalypse is as light as I can go right now.” 

For more views on movies, awards season and other pursuits, follow @GuyLodge on Twitter.

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