Rep. Gabrielle Giffords (D-Ariz.) remains in critical condition at Tucson's University Medical Center today (Jan. 10), but her doctors said they are "much more optimistic" about her recovery from a gunshot wound to the brain Saturday.

The bullet that struck the 40-year-old congresswoman during her public appearance outside a supermarket entered the back of her head , passed through the left side of her brain and exited the front.

Daily CT scans show there has been no progression in swelling of Giffords' brain, Dr. G. Michael Lemole Jr., one of Giffords' surgeons, said.

"No change is good, and we have no change," Lemole, chief of neurosurgery at the University of Arizona, said at a news conference.

Doctors removed part of Giffords' skull to allow her brain to swell without being compressed, which could have increased the chance of brain damage. Swelling typically peaks on the third day after trauma to the brain, though the peak can occur up to 10 days later, Lemole said.

"That's why we're much more optimistic, and can breathe a collective sigh of relief after the third or fourth day," Lemole said.

Giffords can respond to basic commands from doctors, such as raising her fingers or wiggling her toes, Lemole said.

"That implies that not only are centers of the brain working, but they're in communication with one another," he said.

Nurses and doctors test Giffords' responsiveness a few times a day, he said, but it's still too early to measure her psychological function.

Six people were killed and 20 injured by a gunman at the congresswoman's event to meet some of her constituents.

Eight of the injured remain in the hospital, with two people in the intensive care unit, five in serious condition and two in good condition, said surgeon Dr. Peter Rhee, medical director of University Medical Center's Trauma and Critical Care.

"There are still further subsequent surgeries that must be undertaken, but at this phase, in terms of putting things back together, that's being done very well without too much of an issue," Rhee said.

Psychological issues like post-traumatic stress disorder are possible in the patients, he said.

Pass it on: There has been no progression in swelling of Rep. Gabrielle Giffords' brain, after she was shot in the head on Saturday.

Follow MyHealthNewsDaily staff writer Amanda Chan on Twitter @AmandaLChan.