Native American actress Misty Upham never dreamed she would be walking the red carpet at Cannes to showcase a film shot on her reservation.

Upham features in Jimmy P. Psychotherapy of a Plains Indian, focused on the relationship between World War II veteran Jimmy Picard, a Native American Blackfoot, and Georges Devereux, his psychoanalyst.

Upham said like Picard, played by Puerto Rican actor Benicio Del Toro, she is Blackfoot, the largest tribe in Montana. She said she was a direct descendant of the last chief and grew up on the reservation where much of the movie was filmed.

"I had no dreams and no way to make a dream. I had to leave the reservation," Upham, 30, told a news conference on Saturday ahead of the film's "in competition" premiere by French director Arnaud Desplechin.

The movie was inspired by a true story in Devereux's 1951 book Reality And Dream. Set in 1948, the film follows Jimmy as he checks into a military hospital in Topeka, Kansas, that specializes in mental illness for war veterans to be treated for numerous symptoms, including temporary blindness, hearing loss and dizzy spells.

The doctors are baffled by his psychological problems and decide to call in anthropologist and psychoanalyst Devereux (Mathieu Amalric) a specialist in Native American culture who spent two years living with the Mojave Native Americans.

Del Toro, who won the best actor award at Cannes in 2008 for Che, said it was important for him to understand Native Americans to get into his character.