When we refer to an actor's performance as breathtaking, we're usually engaging in hyperbole. Rarely if ever do we mean it actually affected our ability to breathe.

But during "Still Alice," watching the vital, sharply intelligent woman played by Julianne Moore slowly cede her mental faculties - and, most painfully, her identity - to Alzheimer's disease, I found myself frequently needing to gulp in big breaths of air, merely to steel myself for the next scene.

Of course this is partly due to the nature of the material. There's no way to tell a story about Alzheimer's that isn't ultimately devastating, and writer-directors Richard Glatzer and Wash Westmoreland clearly have no intention of sugar-coating the cruelty of this disease.

But as its title suggests, "Still Alice," based on the novel by neuroscientist Lisa Genova, is about one woman, and thankfully we have Moore, one of our most sensitive and nuanced actresses, in the role. She gives a warm, brave and shattering performance here - one that's already earning accolades, and deserves many more before awards season ends.

We first meet Alice, a linguistics professor at Columbia, as she's celebrating her 50th birthday with family. Chic and accomplished, she's managed to work and travel and raise three adult kids in a beautiful home. She and her husband, John (Alec Baldwin), also an academic, live in a lovely brownstone with a great kitchen.

But one day, giving a lecture, Alice suddenly stops, mid-sentence. She can't remember a key word. She recovers nimbly with a joke, but we shudder. Back home, taking her usual jog around campus, she gets lost. The camera blurs, along with the connections in her brain. We shudder again. We know what's coming.

The meeting with the neurologist, for example, where her memory lapses become clear. Her first warning to her husband that something's wrong - he brusquely dismisses her worst fears, as many would to protect themselves. The diagnosis of early onset Alzheimer's. The devastating news that her children might carry the gene.

Time passes - too quickly, of course. Alice tries to keep working, but that proves unrealistic. Also unrealistic: that loved ones, in such circumstances, would behave like saints. Of course they don't. Alice's younger daughter Lydia (an excellent Kristen Stewart), going through a self-indulgent phase, struggles to make room for her mother's affliction. And John, as subtly portrayed by Baldwin, has trouble balancing his devotion to his wife with fears for the future - and his own career goals.

But though these two relationships are key, the movie distinguishes itself from others about Alzheimer's by being, essentially, about Alice's relationship with Alice. It's about her fight to retain what she can of herself - to remain the person that she knows.

A bitter twist, of course, is that Alice is a linguistics professor - an expert in communicating. As her abilities fade, she agrees nonetheless to address a medical conference, and we're so afraid to see her get up there, a trembling shadow of the confident teacher she once was. But this scene -and the message she manages to impart - is one of the film's most powerful.

There's a behind-the-scenes element to the movie that makes it all the more poignant. In 2011, co-director Glatzer saw a doctor about slurred speech and discovered he was suffering from ALS, or Lou Gehrig's disease. He directed the movie using a speech-to-text app on his iPad. Whereas Alzheimer's attacks the mind and ALS the body, both attack one's sense of identity. As the directors express so well in "Still Alice," with the help of Moore's memorable performance, holding onto that identity is what keeps us alive and vital and connected to the world.