Arizona Rep. Gabrielle Giffords is able to respond physically to simple verbal commands despite being shot through the head on Saturday, doctors involved with her care at Tucson's University Medical Center said today.
However, they said, it is not yet possible to know the eventual extent of Giffords' recovery -- or even if she will survive the injury to her brain.
Jared Lee Loughner, 22, allegedly shot Giffords and 19 other people at a political event outside an Arizona grocery store Saturday morning. Six people have died so far, including a federal judge and a child.
Giffords survived and is receiving treatment at Tucson's University Medical Center. The medical center's trauma director, Dr. Peter Rhee, said he remains hopeful about Giffords' chances of survival.
"Everybody is going to be cautious about over-calling it, but I am optimistic," Rhee said today in a news conference. "I was optimistic when I saw the brain yesterday."
He added that the fact Giffords can respond to simple verbal commands is heartening.
"When you get shot through the head and the bullet goes through your brain, the chance of your living is very small and the chance of you waking up and following commands is small," he said.
Neurosurgeons not involved in Giffords' treatment say a number of factors could play a role in her survival and recovery.
"The fact that the bullet left the brain -- less tissue damage is expected. That is a good sign," said Dr. John Boockvar, associate professor of neurological surgery at New York-Presbyterian/Weill Cornell Medical Center in New York.
Rhee said Giffords is responding to commands, which doctors say is also a good sign.
"That's one of the clinical signs used to assess patients with with brain injuries," said Dr. Paul Vespa, director of neurocritical care at Ronald Reagan UCLA Medical Center in Los Angeles.
There are a number of different scenarios that make it possible to survive a gunshot to the brain.
"If it's a a glancing blow that injures the skull and a small amount of brain and doesn't go directly through the whole brain is one case," said Vespa. "People can also survive with parts of the brain missing."
"If the shooter is shorter and the bullet goes just through the frontal lobe, there could be near normal recovery," said Boockvar.
Doctors say smaller caliber bullets do less damage to the brain. They don't penetrate as much of the brain or will bounce off the skull.
Next Few Days Critical for Giffords
Giffords' doctors will have to keep a very close eye on her over the next several days.
"The brain tends to swell over next several days," said Vespa. "Pressure can go up in the brain and the injury can become worse."
Giffords is also at risk for seizures, a stroke and more bleeding.
"[There will also be] two weeks of dealing of ICU [intensive care unit] issues, infections and pulmonary embolism [clot to the lungs]," said Boockvar.
After that, doctors say it will take a couple of months to determine if there has been any loss of brain function and how extensive it is.
The fact that Gifford is only 40 years old works in her favor, since younger people tend to recover more easily.
"It is entirely possible to make a complete recovery," said Vespa.
ABC News' Devin Dwyer, Dean Schabner, Kevin Dolak, Emily Friedman, Lee Ferran and Richard Esposito contributed to this report.