WEDNESDAY, Jan. 12 (HealthDay News) -- Arizona Congresswoman Gabrielle Giffords continues to make progress, her doctors said Tuesday, breathing on her own and moving both arms just four days after an assassin's bullet struck her brain.

"She has a 101 percent chance of surviving," Dr. Peter Rhee, chief of trauma at Tucson's University Medical Center told the Associated Press. "She will not die."

Dr. Michael Lemole, Giffords' neurosurgeon, added that doctors have left a breathing tube in the 40-year-old woman to protect her airways, but she is drawing breaths on her own, and is alert and responding to doctors, the AP reported.

"I'm very encouraged by the fact she's done so well," Lemole said. "Given the violent nature of her injury -- a 9mm bullet through the left side of her brain -- "she has no right to look this good, and she does," the Washington Post reported.

Giffords' doctors said Monday that she was able to follow simple instructions.

They said Giffords responded to verbal commands by raising two fingers of her left hand and even managed to give a thumbs-up, the AP reported. They also said her brain remained swollen, but the pressure wasn't increasing --- a good sign for her recovery.

By Tuesday, the doctors said Giffords could raise both of her arms.

"That's why we are much more optimistic and we can breathe a collective sigh of relief after about the third day," LeMole, who described Giffords' condition as stable, said Monday.

Still, experts said Giffords likely suffered some permanent damage, but it's not yet clear how extensive that damage might be.

Dr. David Langer, director of cerebrovascular research at the Cushing Neuroscience Institutes, part of North Shore/Long Island Jewish Medical Center in Great Neck, N.Y., said: "She's probably going to survive in all likelihood, but months or even a year from now we may not know what her ultimate prognosis will be."

"She'll likely have a deficit in the near term, but we don't know if she'll end up in a wheelchair like James Brady [President Ronald Reagan's press secretary who was injured by a bullet during a 1981 assassination attempt on the president] or a functioning Congresswoman. We can't know," added Langer, who was not involved with Giffords' care.

Giffords was gravely injured, 13 others were wounded, and six people, including a 9-year-old girl, were killed when a 22-year-old man, Jared Loughner, pulled out a semiautomatic Glock pistol in front of a Safeway supermarket in Tucson, where Giffords was meeting constituents. A Democrat, she was first elected to the House of Representatives in 2006.

The fact that Giffords is alive is a bit of a miracle.

According to Langer, 90 percent of people with gunshot wounds to the head die.

"This sounds like a relatively mild form of a gunshot wound and that does happen, based on the trajectory," Langer explained. "Certainly she has the opportunity to be as best as she can, given the aggressiveness of what [her doctors] have done. She has a chance of making a good recovery, but good has a lot of different meanings."

In the Tuesday news briefing, Giffords' doctors revised their interpretation of the path of the bullet, saying they now believe she was shot in the forehead with the bullet traversing the left side of the brain and exiting out the back. They had previously thought the bullet had entered through the back of Giffords' head.

The latest conclusions came from a review of X-rays and brain scans and discussions with two outside physicians, the AP reported.

"The trajectory [of the bullet] itself is not that different but it's reversed. Instead of being shot in the back of the head and exiting from the front, now it's shot into the forehead above the eye, which is the frontal lobe," said Dr. Anders Cohen, chief of neurosurgery and spine surgery at The Brooklyn Hospital Center in New York City.

The key in trying to forecast her recovery lies in whether Rep. Gifford is left-handed or right-handed, he added. Almost all right-handed people are left-brain dominant and the left brain controls cognitive function and some speech. Left-handed people can be dominant on either side.

"If she's left-handed, odds are that the statistics are more in her favor that there'll be fewer cognitive and, perhaps, speech concerns," Cohen said.

Although there's been some speculation that Giffords may be left-handed, this hasn't been reported definitively.

Much also depends on the speed at which the bullet entered the brain. Speed sends off shock waves that can damage surrounding areas. There may also be bleeding or bone fragments, which exacerbate an injury, Cohen explained.

"It's a series of hurdles for the victim," he explained. "Whatever part of the brain that that bullet went through, even if it was a small cylinder of trajectory, that [area] is now permanently injured [but] the repercussions are unknown. There's some permanent and some recoverable damage depending on how injured that part of the brain gets."

"It's a traumatic brain injury [but] she's young and she's otherwise healthy," Cohen said. "She'll be able to recover some and, depending on the injury, her recovery can take up to a year."

More information

The U.S. National Institutes of Health has more on traumatic brain injury.