U.S. Congresswoman Gabrielle Giffords, who was shot at close range by a 22-year-old gunman when she was greeting constituents at a grocery store in Tucson, Arizona, was responsive to simple commands, a positive sign although the Giffords was still in critical condition, doctors said on Sunday morning.

The 40-year-old politician was in a drug-induced coma and is being awakened periodically so doctors can see how she is progressing, Dr. Michael Lemole, a surgeon at the University Medical Center said at a news conference here.

"I am cautiously optimistic," Lemole, chief of neurosurge at the medical facility said. He described, in great detail, how the gunshot went through the left side of Giffords' head and how doctors worked to remove bone fragments to help reduce the swelling and possible damage to the brain.

Giffords is the only patient from Saturday's shooting who remains in critical condition, although she was responsive to commands this morning.

Six people died and 13 others were injured in the killing spree at "Congress at the Corner," Giffords' first public meeting with the public since she was re-elected to the third term at the U.S. Congress.

The gravely wounded congresswoman was in surgery 38 minutes after arriving at University Medical Center (UMC) just before 11 a. m., Dr. Peter Rhee, medical director of the UMC trauma unit.

"We've been very happy with her hospital course," Rhee said.

The single bullet that was shot by the gunman did not pass through both hemispheres, this is fortunate for Giffords, doctors said, as the bullet entered through the back of her skull on her left side and exited through the front.

The congresswoman now faces swelling, a grave danger. For this surgeons have removed about half of her skull on the left side to alleviate the pressure.

Giffords was able to hold up two fingers at the request of doctors before the surgery began, Rhee said, and she was able to follow the same command as of Sunday morning.

All other victims brought to UMC have been upgraded from intensive care. Three remain in serious condition, according to hospital officials.