WEDNESDAY, Jan. 26 (HealthDay News) -- Arizona Congresswoman Gabrielle Giffords was moved to a rehabilitation center in Houston Wednesday morning after her doctors upgraded her condition to good from serious Tuesday night, another step in her remarkable recovery from a gunshot wound to the brain.

Giffords' physicians at Memorial Hermann Texas Medical Center determined that she could be moved to nearby TIRR Memorial Hermann, where her rehabilitation will begin, the Associated Press reported.

Giffords had been in intensive care since her transfer Friday to the Houston hospital from Tucson, where she had been hospitalized since the Jan. 8 shooting that left six people dead and 12 people wounded.

A buildup of fluid in Giffords' brain that concerned doctors over the weekend had started to subside. Late Wednesday, doctors announced that, prior to her transfer, they had removed the catheter used to drain the fluid, the AP reported.

The congresswoman has been making surprisingly strong progress since she was shot in the head Jan. 8. Last week, her doctors at University Medical Center in Tucson highlighted signs of her continuing improvement -- she scrolled through an iPad, identified different colored objects and moved her lips. Still, they weren't sure if she was mouthing words, and they didn't know how well she can see, the AP reported.

The encouraging medical updates out of Tucson indicated that Giffords has a high level of motor and emotional function, experts say.

"The fact that she is able to communicate, that she is able to stand and walk, the fact that she is moving both hands is a good thing," said Dr. Kester Nedd, an associate professor of neurology and director of neuro-rehabilitation at the University of Miami Miller School of Medicine.

"Motor function is a very strong predictor of outcome," he said. In addition, her ability to express emotion and interpret human interactions, which are some of the highest levels of cognitive function, means her chances of recovery are very good, Nedd added.

Giffords was one of 18 people shot by a gunman outside a Tucson supermarket, where the 40-year-old, three-term lawmaker had been meeting with constituents. On Monday, the suspect in the shootings, Jared Loughner, 22, of Tucson, pleaded not guilty to federal charges of attempting to assassinate Giffords and trying to kill two of her aides, the AP reported.

TIRR Memorial Hermann Hospital in Houston is one of the best rehabilitation centers in the country, said Dr. Steve Williams, chief and chairman of the department of rehabilitation medicine at Boston Medical Center and professor and chairman of rehabilitation medicine at Boston University School of Medicine.

"The key things with neurological injuries are when people begin to show signs of recovery very early," Williams told HealthDay last week. "Very early in the ER she was able to squeeze the physician's hand and she has responded to simple commands, and yesterday she was standing."

"The issue is really going to be cognitive function, which is complex reasoning and abstract thinking," added Williams, who was not involved in her treatment but has studied the injury reports so far made public.

Physically, Giffords is making great progress, Williams said, but the full extent of her injuries is still unknown.

Nedd noted that Giffords is already starting at a very high level of functioning. "She was blessed," he said. "A lot of the force of the bullet that struck her was dissipated by the skull and the bullet exiting," he said. Also the injury was not to the deep brain, he added.

One of the first steps in rehabilitation is to help patients regain the ability to take care of themselves. "This is called activities of daily living," Nedd said.

Giffords' rehabilitation will most likely center on her speaking ability and the processes of thinking, Williams said. She may be given medications, such as Ritalin, to stimulate the brain, he said.

One rehab goal is to retrain the brain to take over functions that may have been lost or damaged by trauma, experts said. This is done through repetition, Nedd said. "The brain has the ability to shift function from one part of the brain to another," he said.

Giffords will probably remain at TIRR Memorial Hermann for a month or two, then continue rehabilitation on an outpatient basis, perhaps for a year or more, Williams said.

Giffords, a Democrat, was elected to the House of Representatives in 2006.

Her survival has astounded experts, including 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.

Ninety percent of people with gunshot wounds to the head die, said Langer.

More information

For more information on traumatic brain injury, visit the U.S. National Institutes of Health.