U.S. Rep. Gabrielle Giffords is able to communicate with doctors by following simple commands, a doctor said Sunday.

“We are very encouraged by that,” said Dr. Michael Lemole, Jr., chief of neurosurgery at University Medical Center in Tuscon, Arizona. “I am cautiously optimistic.”

Griffords remained in critical condition Sunday morning after a gunman shot her in the head and then opened fire on a crowd at a political meet-and-greet outside an Arizona supermarket.

The shooting killed six people, including a federal judge and a 9-year-old girl, and wounded 14 others, authorities said. Two people tackled the suspected shooter, stopping a spray of bullets that turned a calm “Congress on Your Corner” event in Tucson into what President Barack Obama later described as an “unspeakable tragedy.”

Giffords was under sedation, said Dr. Peter Rhee, medical director of the UMC trauma center. Doctors will turn off the sedation every so often and allow her brain to begin functioning and “see what her progress is.”

Swelling of the brain is the biggest threat Giffords faces, said Lemole. The bullet traveled through the left hemisphere of her brain from back to front, he said, and “not through some of those critical trajectories” that would have made recovery more difficult. The most traumatic gunshot injuries are when a bullet crosses from one hemisphere to another, he said.

Doctors removed part of Giffords’ skull during surgery in order to keep the brain from pressing against it if it swells, Lemole said.

While the simple commands she can follow may be taken for granted, Lemole said, they actually indicate a high level of brain functioning.

Giffords was the only person remaining in critical condition Sunday, doctors said. The others have been moved out of the intensive care unit.

Lemole said he did not want to speculate on Giffords’ recovery process, but said it is not uncommon for people with such injuries to be in an intensive care unit for at least a week and hospitalized for two to three weeks before beginning a rehabilitative phase, which could last “weeks to months.” “We’ve seen the full gamut,” he said.

Local authorities took custody of 22-year-old suspect Jared Lee Loughner at the scene, law enforcement sources said. The Pima County Sheriff’s Department said the suspect had been transferred to FBI custody.

Early Sunday morning, investigators released a surveillance photo of a man between 40 and 50 years old who is “possibly associated with the suspect.”

The dark-haired man was spotted “in proximity” to the suspect at the location where the shooting occurred. Authorities were interviewing witnesses to determine whether there was a connection between the man and Loughner.

(Source: CNN)